Institut für Pflanzenproduktion und Agrarökologie in den Tropen und Subtropen

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Soil erosion in Andean Cropping Systems: The impact of Rainfall Erosivity
(2002) Sonder, Kai; Leihner, Dietrich
Rationale and methods The Andean region of Colombia, 30% of the country, has about 15% of the tot. population and 50% of the rural population. A great part of the countries food-crops are grown on the hillsides of the region, which are severely degraded or threatened by degradation. The objectives of the present study were: a) to determine the applicability of the USLE rainfall erosivity factor to the Andean Region, particularly the energy-intensity term b) to calculate long-term erosivity data c) to establish the long-term erosivity of two soil types in the research area d) to evaluate the yield and soil conservation performance of several cassava-based cropping systems. Research was carried out at two sites in the Cauca department in the southwest of Colombia. Santander de Quilichao is located at 3o 6' N, 76 o 31' W, at an altitude of 990 m a.m.s.l., with an annual precipitation of 1,789 mm and an average temperature of 23.7 o C. Mondomo, which lies 2o 53' N, 76 o 35' W at an altitude of 1,450 m a.m.s.l., has an annual precipitation of 2,133 mm and an average temperature of 18.2 o C. The soils at both sites belong to the inceptisols, which form about 77% of the soils of the Cauca departments. In 1987 erosion plots were established at both sites on slopes of between 7% and 20% consisting of 8 treatments and 3 repetitions at Quilichao with 2 at Mondomo. During the research in this study, the 8 treatments comprised: 1) Continuous bare fallow, 2) Traditional cassava-based rotation, 3) Continuous sole cassava, 4) Cassava-based rotation with minimum tillage and mulch, 5) Cassava-based rotation with two previous years of bush fallow, 6) Cassava-based rotation with vetiver grass barriers, 7) Cassava-based rotation with legume strips, and 8) Cassava-based rotation with improved fallow element. Rainfall erosivity Drop size distribution measurements with a Joss-Waldvogel Distrometer showed that the USLE R factor is applicable for the research region as no significant differences were found between the measured kinetic energy of rainfall events and calculated values according to the USLE. The average annual r-factor values during the 12 year research period for Quilichao and Mondomo were 10,037 and 9,016 MJ ha-1 mm h-1 a-1 respectively. A highly significant relationship was found between a modified Fournier index based upon average monthly rainfall amounts and the equivalent monthly r-factor values. Soil losses K-factor values measured of 0.017 t h MJ-1 mm-1 at Quilichao and 0.011 t h MJ﷓1 mm-1 at Mondomo may be regarded as being between medium and low, although soil losses on the bare fallow plots were very high due to the extreme erosivity of the climate. Total soil losses in Quilichao on the bare fallow from 1986 to 1998 were 1,840 t ha-1. In Mondomo it was 2,380 t ha-1. From June 1994 to July 1997, the 7 cropped treatments in Quilichao showed susceptibility to erosion in the following order (from high to low): Sole continuous cassava, bush fallow >> farmer rotation, legume strips > improved fallow > minimum tillage, grass barriers. In Mondomo the susceptibility to erosion for the same period was: Sole continuous cassava >> legume strips >> bush fallow > improved fallow, farmer rotation > grass barriers, minimum tillage. When calculating soil loss for a representative plot only the minimum tillage and grass barrier treatments reached levels below the tolerable average annual soil losses under both the Quilichao and Mondomo conditions.The erosivity and erodibility values for the whole 12-year duration of this project showed that there is a highly significant relationship between annual soil loss amounts and the R-factor of the USLE. The continuous bare fallow plots showed strong declines of organic matter at both sites. Yield performance The two conservation treatments, minimum tillage and grass barriers, showed no significant differences regarding yield compared to the widely used continuous cassava system. The farmer rotation treatment showed the highest yield levels, but there were no significant differences between this treatment and the minimum tillage treatment at Mondomo and Quilichao. Conclusions The results confirm the high erosivity of the climate and support the necessity of maintaining permanent soil cover. The proven applicability of the R-Factor of the USLE for the region and the long-term soil erodibility values determined should enable the potential erosion risk to be estimated and appropriate soil conservation measures offered. Of the cropping systems evaluated, both the minimum tillage and the vetiver grass barrier treatments proved to be interesting alternatives to the local cropping systems as they reduced soil erosion to a sustainable level and at the same time reached or even surpassed the yields of the traditional cassava monocropping. All the other systems would lead to degradation if long-term permanent cropping was practised.
Spatial undergrowth species composition in oil palm (Elaeis guineensis Jacq.) in West Sumatra
(2003) Germer, Jörn Uwe; Sauerborn, Joachim
The area planted to oil palm expanded during the last decades substantially, making it become the world's second most important oil crop. Despite its economic significance the oil palm remains remarkably unknown. Little attention is paid also to the oil palm undergrowth, though important in stabilizing the agro-ecosystem in plantations. Comprehensive knowledge of undergrowth species adapted to specific ecological niches in oil palm plantations is essential to investigate their function in and potential benefit to the oil palm agro-ecosystem. The objectives of the conducted research were to develop a reproducible approach for phytosociological investigation in oil palm plantations and to accomplish a general inventory of the vascular plants associated with oil palm in a plantation in West Sumatra. Additionally it was aimed to study the undergrowth heterogeneity within the fields and the distribution of species in the plantation in response to solar radiation below the palm canopy, soil type and physical and chemical soil parameters. A rich diversity of 298 species, 186 dicotyledonae, 77 monocotyledonae and 35 pteridophyta (ferns and allies), representing 81 families was identified in the research area. Similar to rainforests, plants with a high consistency were few, while most of the species occurred only sporadically in the oil palm undergrowth. In average 36 species were found in each of the 100 sampled relevés. The 8 most frequent species were identified as an abstract plant community: Mikania micrantha H.B.&K., Pouzolzia zeylanica Benn., Ageratum conyzoides L., Sporobolus diander Beauv., Nephrolepis biserrata (Sw.) Schott., Pityrogramma calomelanos (L.) Link, Lygodium microphyllum (Cav.) R.Br. and Stenochlaena palustris Bedd. Due to particular management practice, oil palm fields can be zoned in harvesting path, palm circle and inter-row. Species that were mainly found in the inter-row were: Diplazium esculentum (Retz.) Sw, Cyclosorus interruptus (Willd.) H.Ito, Nephrolepis biserrata and Christella dentate (Forssk.) Brownsey & Jermy. Plants that were found primarily in the other zones were small herb species such as Hedyotis corymbosa Lam., Limnophila rugosa Merrill, Borreria setidens (Miq.) Boldingh and Peperomia pellucida H.B.&K., the sedges Fimbristylis miliacea Vahl and Cyperus kyllingia Endl. as well as the grass Sporobolus diander. It was found that the palm canopies developed slower on histosol than on fluvisol and assumed that the main reason for this difference was the lower nutrient pool in low-density organic soil. Melliferous species, which are often important as hosts for pest antagonists, were infrequent where less light was available. In the inter-row a distinct shift from a creeper and grass to a fern and non-creeper dicotyledonae dominated undergrowth was observed with falling levels of solar radiation. Species consistently more frequent in less shaded sampling sites throughout the research area were: Basella alba Linn., Calopogonium muconoides Desv., Commelina diffusa Brum.f., Imperata cylindrica Beauv., Pueraria phaseoloides Benth. and Sporobolus diander whereas Ageratum conyzoides, Christella dentata, Diplazium esculentum, Peperomia pellucida, Phyllanthus debilis Willd., Pouzolzia zeylanica and Sparganophorus villantii Crantz preferred more shaded environments. The soil analyses revealed that the soil carbon content was not only distinctly different between histosol and fluvisol, but also between individual sites on the two soil types. Next to the carbon content the effective cation exchange capacity varied largely between sites. The physical soil properties were stable within the sites, while the chemical properties were significantly influenced by fertilization. Species abundance per relevé was significantly higher on fluvisol than on histosol, while the difference in the total number of species between the soil types was small. 11 species showed a preference towards low soil carbon content: Ceratopteris thalictroides (L.) Brongn., Christella dentata, Christella parasitica (L.) Lev., Diplazium esculentum, Eleusine indica (L.) Gaertn., Hedyotis corymbosa, Pleocnemia irregularis (C.Presl) Holtt., Polygonum barbatum L., Selaginella plana Hieron., Sphaerostephanos polycarpus (Bl.) Copel. and Stachytarpheta indica Vahl. Accordingly the presence of two species: Borreria latifolia (Aubl.) K. Schum. and Dicranopteris linearis J. Underw. augmented with increasing soil carbon content. In the sampling sites marked by high ECEC ferns were dominant. On fluvisol 11 out of 18 species that occurred more frequently where the ECEC was higher were ferns and on histosol 3 out of 12 species respectively. The distinct difference of soil carbon content blanketed, apart form the ECEC possible effects of other soil properties on the undergrowth species composition.
Biodiversity and arthropod abundance in the upland of Leyte, Philippines
(2005) Szinicz, Gundula; Sauerborn, Joachim
In the humid tropics of SE-Asia the last primary forests are dwindling at an alarming rate. In many regions cultivated and degraded land outnumbers by far natural ecosystems. In the upland of Leyte island this is due to commercial and illegal logging activities and intensive slash-and-burn agriculture. The loss of the natural vegetation cover is accompanied by a decrease in diversity of fauna and flora, consequently also in ecosystem services and interactions, thus destabilizing the system and finally leading to degradation. To further preserve and restore natural biodiversity landscapes dominated by man need to be included in an overall research strategy. So far only few studies focus on the biodiversity of cleared and converted land adjacent to natural areas in the tropics. This study was conducted in a Philippine upland area and focused on interchanges of insects between the natural and the managed landscape. Two questions were approached. (1) Which structures and components of the cultural landscape are of significance for conserving arthropod biodiversity, and (2) are there species which originate from the natural forest and are able to become resident in the man-made systems? In order to answer these questions insect- and plant surveys as well as the movement patterns of selected insect species were examined along a gradient from the natural forest through the agricultural land. So as to define the effects of habitat destruction on the arthropod community of the research area arthropod communities of different habitats between the natural and agricultural ecosystems with increasing distance to the forest, in relation to the vegetation were compared. Insect sampling was carried out using modified Malaise traps, whereby four habitats were considered: (a) forest interior, (b) forest margin, (c) vegetable fields and (d) chayote ((Sechium edule (Jacq.) Sw. (Cucurbitaceae); the only perennial vegetable of the area) fields. These traps allowed a separate catch for each of the two arrival sides, whereby the one was always opened to the forest and the other to the field. Trapping was set up for a total of 18 months in 2001 and 2002 at three sites with the four habitats each. Arthropod diversity, composition of the arthropod community and trophic guild composition at habitats were determined for each habitat and arrival side. Obtained results are presented and discussed with regard to first: arthropod diversity and community composition along the transect from natural through agricultural systems; second: abundance patterns of selected species in natural and agricultural systems and third: abundance patterns of selected species within the agricultural land. It was found that plant diversity, vegetation structure and taxonomic composition as well as differences in the turnover of the vegetation at habitats (productivity of vegetation) influence arthropod groups and species in the study area in different ways which could not be generalised. Further, the relationships of insects between the natural forest and the open agricultural land were considered. In order to identify species that occur in the forest as well as in the open country, first, insects at sites of the forest interior, the forest margin and the agricultural land, were recorded using modified Malaise traps. Then, movement patterns of selected species were determined based on their abundances at the different habitats and arrival sides. In addition it was tried to find out whether major pest species of the cultivated crops show any relationship to the adjacent natural forest, and whether species originating from the forest (non-pest species) are able to colonize open country. The results indicate that the habitat of the pest species considered is limited to the cultivated land and does not include the forest. None of the non-pest species recorded in this study would be able to exist permanently in the agricultural area. They all depend on a closed forest habitat and therefore will become extinct as the forest disappears with proceeding slash-and-burn agriculture. However, some but not all of the pest and forest species were regularly recorded from the forest margin. Finally it was focused on relationships of insects between perennial and consecutive changing vegetable crops. Two kinds of habitats were distinguished: (i) frequently disturbed and rotational changing vegetables with simple architecture; (ii) rarely disturbed stands of chayote, with complex architecture. The impact of changing crop and weed species composition and the agricultural practices (soil preparation, planting, weeding, harvest) applied on the abundance of selected insect species and the question whether stands of chayote are used as refuge as long as conditions in the seasonal vegetables become unfavourable due to agroecosystem management applied were analysed. The insect species investigated include phytophagous specialists and generalists as well as beneficials (predators and pollinators). It only was possible to generalize movement patterns regarding significance of abundance variations at habitats and at opposite arrival sides of the traps in each habitat. With respect to the population development of the species in relation to cropping patterns and agricultural practices applied no common patterns could be determined. The results contribute to the assessment of the effects of man-made habitat conversion on the arthropod fauna in tropical ecosystems. The identification and classification of habitats and their interactions might enhance the understanding of ecosystems in order to make aware the need to preserve and restore biodiversity.
Pathogenitätsfaktoren und induzierte Resistenz in der Interaktion von Orobanche ramosa L. und Nicotiana tabacum L.
(2005) Gonsior, Guido; Sauerborn, Joachim
Parasitic weeds of the genus Orobanche, cause severe damage to vegetables, legumes and sunflower in Europe, the Middle East and North Africa. Recently there is evidence for increasing occurrence of branched broomrape (Orobanche ramosa L.) in rape and tobacco cultivars in France and Germany. This research concerns on biology and pathogenicity of O. ramosa with special focus on the interactions with the host plant. In addition mechanisms of induced resistance of the host plant against the parasite were considered. The results showed genetic differences between the populations of O. ramosa in Germany, which partially parasitize different hosts. As possible factors of pathogenicity the accumulation of reactive oxygen species and a high peroxidase activity together with a high antioxidative capacity caused by the phenylpropanoids Verbascosid and Oraposid were identified. The control of branched broomrape was possible by application of agents, which are described to induce disease resistance. Control of branched broomrape could be based on systemic acquired resistance (SAR) as well as on induced systemic resistance (ISR). As defense mechanisms in tobacco roots against O. ramosa the biosynthesis of the hydroxycoumarin scopoletin and a significant increase of soluble and bound phenolics was discussed. This is underlined by a high activity and an increased expression of phenylalanine ammonia-lyase (PAL) the key enzyme of the phenylpropanoid pathway. Beside phytoalexin production we recognized an increased activity of peroxidases in Orobanche ramosa infected tobacco roots. Further it could be shown that the plant hormone Ethylene as well as the regulation of the sugar metabolism have importance for the resistance of the host plant.
Diversity in the tropical multipurpose shrub legumes Cratylia argentea (Desv.) O. Kuntze and Flemingia macrophylla (Willd.) Merrill.
(2006) Andersson, Meike S.; Schultze-Kraft, Rainer
Cratylia argentea (Desv.) O. Kuntze and Flemingia macrophylla (Willd.) Merrill are promising tropical multipurpose shrub legumes. Both are drought-tolerant, well adapted to low-fertility, acid soils, and especially suited for low-input smallholder production systems in the sub-humid and humid tropics. They can be used e.g. as dry season forage supplementation, live soil cover or mulch, erosion barrier hedges, and shade-providing shrubs in young coffee and cocoa plantations. Germplasm collections were assembled from the wild-legume flora in Brazil (C. argentea) and Southeast Asia (F. macrophylla), but research and development are so far based on only a few accessions. Knowledge about the extent of genetic diversity within these collections is very limited. In addition, the potential utilization of F. macrophylla is so far limited by poor forage quality and acceptability of the few evaluated accessions. The objective of the present study, conducted in a research cooperation with the International Centre for Tropical Agriculture (CIAT), Cali, Colombia, was to assess the diversity in the germplasm collections of C. argentea (38 accessions) and F. macrophylla (69 accessions) in terms of morphological and phenological traits, agronomic and forage quality traits, and molecular markers, and to identify superior genotyes. Based on these different characterization approaches, the objective was furthermore to establish core collections for F. macrophylla, and to compare and validate the different strategies, giving particular consideration to their practical implications (time and cost efficiency) for the application to small collections of perennial wild tropical legumes. Cratylia argentea High diversity in terms of phenological and agronomic as well as forage quality traits was detected in the collection, with scope for plant improvement in terms of higher dry season DM production. Accessions CIAT 18674 and 22406 were identified as promising for further evaluation since they were similar to the commercial cultivar "Veraniega" in terms of forage quality, and superior in terms of DM production, particularly in the dry season. Molecular marker analysis with RAPDs showed that the genetic diversity in the collection was relatively low and fairly homogeneously distributed. Accessions CIAT 22373, 22378, 22380, 22381 and 22411 were identified as possible duplicates. Flemingia macrophylla High diversity in terms of morphological and agronomic as well as forage quality traits was detected among the 69 accessions. The identification of four morphotypes in the collection probably has taxonomic implications. Scope for plant improvement was identified with respect to forage quality - one of the species´ main limitations. Accessions CIAT 18437, 21083 and 21090 had similar DM production and higher digestibility than the control accession, and were virtually free of extractable condensed tannins. Problems with low palatability and low seed production of these promising accessions need to be further studied. Genetic diversity in F. macrophylla was higher than in C. argentea, and corresponded closely to the four morphotypes revealed by conventional characterization. Various duplicate accessions were identified, and evidence was provided that the non-Asian accessions are not native to their collection site regions, but rather introduced from Southeast Asia. The results have direct applications for plant improvement of these promising multipurpose legumes. The superior genotypes selected in this study will be used in work with farmers in CIAT-research sites in Central America and distributed to partners. It must be recognized, however, that the diversity assessed is influenced by the climatic and edaphic conditions at the site where the studies were conducted. Therefore, multilocational trials should be considered with a selected subset (including the promising accessions) of C. argentea and F. macrophylla i) to assess the extent of genotype x environment interaction, and ii) to identify genotypes with consistently high performance in a range of distinct environments. Research on the reproduction system of both species is urgently required to determine the potential extent and impact of outcrossing. Beyond the immediate application of these species for farmer utilization, the results of the use and comparison of different approaches to assess diversity and to establish core collections can help to improve germplasm management and characterization of wild tropical legume species in general. Random sampling has been identified as a valuable and resource-efficient strategy for the creation of core collections when no additional information about accessions is available, and in the absence of adequate funds. The validation of the findings of this study with a broader range of perennial tropical wild legumes is necessary to assess their applicability to other species.
Rainforestation farming on Leyte island, Philippines - aspects of soil fertility and carbon sequestration potential
(2007) Marohn, Carsten; Sauerborn, Joachim
This study aimed at investigating rainforestation systems in Leyte, Philippines, under different aspects: Characterisation of typical soils in Leyte with respect to physical, chemical and biological parameters relevant for tree growth, possible contributions of rainforestation to restoring soil fertility, performance of a recently planted rainforestation system under different microclimatic and soil conditions, potential of the rainforestation approach for projects under the umbrella of the Clean Development Mechanism (CDM). Soils in Leyte can be grouped into a volcanic and a calcareous category. The latter were formed on coralline limestone and are high in pH and Ca2+ and Mg2+. Contents of organic matter are high while concentrations of plant available PBray are low. Volcanic soils are characterised by low pH and CEC as well as extremely low PBray contents. Organic matter levels are below those of the calcareous soils but still moderate. In any analysed soil, N would not limit tree growth. Pore volume and water infiltration were propitious for all sites, which is relevant in the context of erosion. For calcareous soils, drought and reduced rootability due to clayey subsoil posed the most relevant constraints. The frequently claimed role of rainforestation in the rehabilitation of degraded soils was assessed in a paired plot approach. Chemical and biological soil parameters under 10 year old rainforestation were contrasted with adjacent fallow or Gmelina sp. Clear tendencies across all seven sampled sites were lower available Mg2+ and pH under rainforestation. Other differences were less distinct. Generally, a depletion of soil reserves e.g. in basic cations can be explained by uptake into the plants. A feed-back of these elements to the topsoil via leaf litter, however, could be observed only for available P. In conclusion, plant uptake of single elements can reach orders of magnitudethat reduce soil stocks. At the same time, generally lower pH under rainforestation may have contributed to elevated losses, especially of basic cations. A general improvement of the sampled soils in terms of chemical or biological characteristics through rainforestation could not be observed. To evaluate plant performance six timber and four fruit species, most native, were interplanted on a 1ha plot. Rainforestation, commonly understood as high-density closed canopy system was modified to a less dense 5x5m grid, interplanted with Musa textilis. The plot varied strongly on a small scale due to heterogeneous canopy closure and relief. Methodologically, the entire area was divided into 10 subplots in representative positions to be sampled. Soil physical and chemical properties, microbial activity, PAR and root length density were determined and correlated to plant survival and growth at consecutive inventories. For Musa textilis, the most sensitive species, which was used as an indicator, logistic regressions were calculated to determine the influence of all relevant parameters on survival rates. The most important predictors for survival were organic matter contents, parameters related to biological activity and leaf litter production, which resembled canopy closure and thus indirectly light intensity and soil moisture. To assess growth, multiple regressions were formulated for biomass at five inventories. Corg and NLOM were the most relevant variables determining the regressions used for biomass and growth of abaca. Assessing the potential of rainforestation for Clean Development Mechanism (CDM) measures, amounts of sequestered CO2 during 10 and 20 years, respectively, were estimated under different management options using the WaNuLCAS model. Despite all given uncertainty associated with modelling, one very obvious finding was the dominant role of soil carbon for the plot balance: Appropriate soil management, especially during land preparation (e.g. clearing vs. enrichment planting) is of paramount importance. Looking at the modelled contribution of various tree species to the carbon balance, Musa textilis had a significant influence only during the very first years; later on, the principal share of carbon was bound in the tree component. Here, exotic Gmelina arborea built up biomass more quickly than a rainforestation plot composed of native Shorea contorta and Durio zibethinus, but was then overtaken. In absolute quantities of CO2 sequestration, magnitudes matched inventory and modelled data given in various literature sources for Leyte and the Philippines. Relative to earlier inventory data from two rainforestation sites, modelled values overestimated growth.
Biological control of Striga hermonthica (Del.) Benth. using formulated mycoherbicides under Sudan field conditions
(2008) Zahran, Eldur; Sauerborn, Joachim
Striga hermonthica is a parasitic flowering plant belonging to the family Orobanchaceae. It is a root parasite that attacks sorghum, maize, millet and several grass weeds in the semi-arid Tropics. In Sudan, Striga is widespread in irrigated and rainfed areas and considered the main biotic constraint in production of sorghum, the main staple food for the majority of Sudanese people. More than 500,000 hectares under rainfed cultivation are heavily infested with Striga, which commonly results in significant yield losses of 70 ? 100%. It has become obvious that there is no simple, fast and inexpensive solution to the Striga problem in Africa. Biological control is considered a potential cost-effective and environmentally safe means for reducing weed populations in crops, forests, or rangelands where low profit margins prevent large herbicide expenditure. Biological control using microorganisms (especially phytopathogenic fungi) showed a high efficacy in controlling S. hermonthica under controlled and field conditions. However, so far it did not come to practical field application. This could be attributed to environmental obstacles or due to the lack of appropriate delivery systems. The pathogenicity of two fungal isolates indigenous to Sudan (Fusarium nygamai [FN] and F. ?Abuharaz? [FA] isolate) against Striga has been studied using infected sorghum grains or a spore suspension as inoculum. These formulations were very effective in controlling Striga under controlled and natural conditions; however, a high level of fungal inoculum (approximately 800 kg ha-1 for the grain inoculum) would be required for effective control, which arises a lot of problems e.g. concerning sterilization and transportation. Such problems can be overcome by adopting an appropriate formulation technology. Granular formulations such as ?Pesta? and alginate pellets were found to be suitable delivery systems for controlling weeds. ?Pesta? granules are made by encapsulating bioagents in a gluten matrix. Alginate formulations are prepared by incorporating the biocontrol agent?s propagules in a sodium alginate solution, which is dripped to a calcium chloride or calcium gluconate solution. Alginate pellets are then formed by ionotrophic gelation. The main objectives of this study were: (a) to study the efficacy of the two Fusarium species in controlling Striga under field conditions using ?Pesta? and alginate formulations, (b) evaluate the effect on sorghum yield, (c) determine the optimum dose of the formulated material, (d) investigate the persistence of the formulated fungal isolates in the soil, and (e) study the efficacy of seed treatments as an alternative delivery system. Furthermore, for environmental safety reasons the newly isolated F. ?Abuharaz? isolate was tested for its ability to produce some of the most important mycotoxins. Harvested sorghum seeds out of the fungus-treated plots were also investigated for their mycotoxins content. A prerequisite to be able to formulate biocontrol fungi is the development of an inexpensive method of inoculum production that yields sufficient biomass containing viable, highly virulent propagules. Chlamydospores are the soil-persisting propagules of many Fusarium species and considered as ideal propagules to be used in granular formulations. For this reason, finding a medium suitable for the production of chlamydospores by the two Fusarium isolates was one of the specific objectives of this study. Different media were tested among them Special Nutrient-poor Broth (SNB) + yeast gave the highest number of chlamydospores (105 ml-1) in both isolates throughout the incubation period. However, both isolates generally did not form sufficient chlamydospores to be used within a bioherbicide formulation. Richard?s solution gave the highest number of microconidia (108 ml-1) after five days of incubation and hence it was selected as growth medium for formulation purposes throughout this study. FN and FA were successfully formulated in ?Pesta? and alginate granules amended either with 10% wheat flour or 6% sorghum flour or yeast extract. Alginate granules generally gave higher numbers of colony forming units (cfu) per g of formulated material compared to ?Pesta?. Alginate preparations amended with 6% sorghum flour or yeast extract had significantly higher cfu compared to the alginate formulation using 10% wheat flour. Yeast extract amendment further increased the number of cfu by about 38 and 32% for FN and FA, respectively, compared to sorghum amendment. In the first field experiment (2003/04), a screening for the suitable dose of ?Pesta? granules per planting hole to control Striga was conducted together with the investigation of a seed coating treatment as an alternative delivery system of the biocontrol agents. The ?Pesta? technology showed a potential to be used as a delivery system to control S. hermonthica under field conditions. Both ?Pesta?-formulated Fusarium isolates were able to delay Striga emergence, reduce the total number of Striga shoots and induce disease symptoms on all growth stages of Striga plants, irrespective to the dose and method of application used. The highest control efficacy was achieved by applying FA at 1.5g, which reduced the total number of parasite shoots by 82 % and the number of healthy Striga shoots by 88% compared to the untreated control. As a consequence, sorghum biomass and sorghum 100-seed weight were increased by 86 and 110%, respectively. FN and the combination of the fungal isolates were slightly less efficient in controlling the parasites. 1.5 g ?Pesta? granules per planting hole was found to be the optimum dosage for Striga management since increasing the dosage did not result in a significant improvement of control. In the second season (2004/05), the efficacy of alginate formulations amended with 10% wheat flour applied at 1.5g/planting hole was evaluated in addition to the ?Pesta? formulation for controlling Striga under field conditions. Alginate granules were able to delay Striga incidence significantly and reduce the total number of Striga shoots by 64 ? 78 % compared to the control early in the season. In contrast to the first season, fungal isolates formulated in ?Pesta? granules had no pronounced effect on delaying Striga emergence, however, ?Pesta?-granulated Fusarium species were able to reduce the total number of Striga shoots by 42 ? 55 % compared to the control early in the season. By the end of the season, the effect of both formulations on the total number of Striga shoots became negligible, but they significantly increased disease incidence on Striga shoots compared to the untreated control. FA formulated in ?Pesta? or alginate pellets was especially effective in this regard, causing disease in 74 and 80% of the Striga plants and reducing the total number of healthy Striga shoots by 55 and 60% compared to the control, respectively. FA applied as ?Pesta? granules was the most effective treatment in reducing Striga biomass by 58 % compared to the control which was positively reflected in an increased sorghum grain yield (63%) and sorghum straw yield (73%) compared to the control. The reduction of the efficacy of the ?Pesta? formulation in controlling Striga in the second season compared to the first season can probably be attributed to three reasons. These include a) climatic conditions, which differed from the first season in higher temperatures coupled with lower rainfall and low relative humidity, b) sodicity problems in the fields which might have affected the proliferation of the fungi in the soil and c) an inhibitory effect of the metabolites of the applied insecticide Sevin (active ingredient Carbaryl (1-naphthyl N-methylcarbamate)) on the virulence of soil fungi. Furthermore, an outdoor pot experiment was conducted to study the efficacy of alginate formulations with different amendments (wheat flour, sorghum flour and yeast extract) in comparison to the ?Pesta? formulation and seed treatments on controlling Striga. In this experiment, FA formulated as ?Pesta? granules was the most effective treatment and successfully inhibited Striga emergence until the end of the season. This was reflected in a significantly increased sorghum plant height (by 80%) and sorghum shoot dry weight (400%) compared to the negative control. Fusarium species in alginate granules also delayed Striga emergence and reduced the total number of Striga throughout the growing season. The best efficacy was obtained by FA, which reduced the total number of Striga shoots by 71% (using 10% wheat flour) and 84% (6% sorghum flour or yeast extract) compared to the control. Likewise, it reduced the proportion of healthy Striga shoots by 71%, 88% and 84%, respectively, and Striga biomass by 50%, 81%, and 89%, respectively. Alginate formulations generally also significantly increased sorghum plant height by up to 80% and sorghum shoot dry weight by 200 to 400% compared to the control. It can therefore be summarized that of the investigated fungal isolates and granular formulations FA formulated in ?Pesta? granules showed the best efficacy in controlling Striga under field and controlled conditions. The ability of FA to produce trichothecene mycotoxins that could be a hazard to humans or animals was assessed from samples of the fungus growing on autoclaved wheat grains. Additionally, samples of harvested sorghum seeds from various plots inoculated with the biocontrol agents were investigated for the content of trichothecene mycotoxins. None of the following toxins were either produced by FA or translocated to harvested sorghum seeds under field conditions: nivalenol, fusarenon X, deoxynivalenol, 15-actetyldeoxynivalenol, scirpentriol, monoacetoxyscirpenol, diacetoxyscirpenol, T-2 triol, HT-2 toxin, T-2 toxin and neosolaniol. A simple seed coating treatment using fine ?Pesta? granules and gum Arabic as adhesive material also showed a potential to control Striga in the first season experiment. It was able to reduce the total number of Striga shoots by more than 55% compared to the control. Consequently, sorghum biomass was increased by 54 ? 67% and sorghum100-seed weight by 70%. The effects were comparable to that caused by chemical control using 2,4-D. To improve the efficacy of seed coating under field conditions for the second season experiments, the effect of five types of adhesive materials (2 types of cellulose, 2 types of organic polymers and a clay) on growth and sporulation of FA and FN were tested in solid and liquid media. Cellulose 1 and 2 were found to enhance radial growth of both isolates but did not increase sporulation in liquid media. Organic polymer 2 was found to retard both radial growth and sporulation of the two isolates. Organic polymer 1 and clay significantly enhanced the production of chlamydospores, especially by FA, compared to Richard?s solution alone or amended with the other tested materials. For this reason one of them was suggested to be used for seed coating in addition to Arabic gum. Sorghum seeds were coated by a private company (SUET Saat- und Erntetechnik GmbH, Eschwege, Germany), using air-dried fungal propagules fermented on 1.5 % (w/v) sorghum straw. Arabic gum was observed to give a better coverage of sorghum seeds and higher cfu per seed (4 x 104 [FA] and 19 x104 cfu [FN]) compared to the second adhesive material. Coating sorghum seeds with the biocontrol agents did generally not result in a significant reduction of Striga shoots in the field, but some of the seed-coating treatments were very efficient in inducing disease symptoms on Striga shoots. Especially FN coated with Arabic gum and FA applied to the seeds in fine ?Pesta? granules increased the proportion of diseased Striga shoots significantly compared to the control by 79%. In the pot experiment, the fungal isolates applied as a seed coating neither resulted in a significant reduction of Striga shoots. Nevertheless, FA applied to sorghum seeds using the adhesive material provided by SUET reduced the total number of Striga plants by 52% compared to the control at the end of the season. FN in the same treatment significantly increased the proportion of diseased Striga by 77% at the end of the season. The effect of seed coating on increasing sorghum plant height and dry matter was lower than that caused by the granular formulations and not statistically significant compared to the control. From the obtained results it can be concluded that both granular formulations applied to the planting holes and seed coating can be used as effective delivery systems for biocontrol fungi and can be adopted under field conditions to reduce Striga infestation. However, the granular formulations showed a higher efficacy in controlling Striga. Inoculum type and concentration as well as nutritional amendments to the formulations should be further optimized in future investigations.
Nutrient management and spatial variability of soils across scales and settlement schemes in Zimbabwe
(2010) Cobo Borrero, Juan Guillermo; Cadisch, Georg
Decline in soil fertility in Africa is one of the most limiting biophysical factors to agricultural productivity, as nutrient mining and low yields are strongly related. However, the high heterogeneity in management together with different biophysical, socio-economical and political conditions across each African agro-ecosystem make blanket recommendations difficult. Thus, acknowledging heterogeneity, and moreover quantifying it at different spatial scales, are the first steps to make adequate recommendations for the different actors. The goal of this thesis was to develop new methodological approaches to better understand nutrient management and spatial variability of soils across different scales in African agro-ecosystems, having various small-holder settlement schemes in Zimbabwe as a case study. Firstly, the thesis includes a literature review on nutrient balances in Africa, which was carried out to illustrate main approaches, challenges, and progress made, with emphasis on issues of scale. The review revealed that nutrient balances are widely used across the continent. The collected dataset from 57 peer-reviewed studies indicated, however, that most of the balances were calculated at plot and farm scale, and generated in East Africa. Data confirmed the expected trend of negative balances for N and K (>75% of studies had mean values below zero), while for P only 56% of studies showed negative mean balances. Several cases with positive nutrient balances indicated that soil nutrient mining cannot be generalized across the African continent. Land use systems of wealthier farmers and plots located close to homesteads mostly presented higher N and P balances than systems of poorer farmers (p<0.001) and plots located relatively farther away (p<0.05). Partial nutrient balances were significantly higher (p<0.001) than full balances calculated for the same systems, but the latter carried more uncertainties. The change in magnitude of nutrient balances from plot to continental level did not show any noticeable trend, which challenges prevailing assumptions that a trend exists. However, methodological differences made a proper inter-scale comparison of results difficult. Actually, the review illustrated the high diversity of methods used to calculate nutrient balances and highlighted the main pitfalls, especially when nutrient flows and balances were scaled-up. In fact, gathered information showed that despite some few initiatives, appropriate scaling-up methods are still incipient. In the next chapter, the nutrient balance approach was applied in NE Zimbabwe. Three smallholder villages located in a typical communal area (colonial settlement from 1948), and in old (1987) and new (2002) resettlement areas (post- land reform settlements), on loamy sand, sandy loam and clay soils, respectively, were selected to explore differences in natural resource management and land productivity. Focus group discussions and surveys were carried out with farmers. Additionally, farmers in three wealth classes per village were chosen for a detailed assessment of their main production systems. Maize grain yields (Mg ha-1) in the communal (1.5-4.0) and new resettlement areas (1.9-4.3) were similar but significantly higher than in the old resettlement area (0.9-2.7), despite lower soil quality in the communal area. Nutrient input use was the main factor controlling maize productivity in the three areas (R2=59-83%), while inherent soil fertility accounted for up to 12%. Partial N balances (kg ha-1 yr-1) were significantly lower in the new resettlement (-9.1 to +14.3) and old resettlement (+7.4 to +9.6) than in the communal area (+2.1 to +59.6) due to lower nutrient applications. P balances were usually negative. Consistently, maize yields, nutrient applications and partial N balances were higher for the high wealth class than in poorer classes. It is argued that effective policies supporting an efficient fertilizer distribution and improved soil management practices, with clearer rights to land, are necessary to avoid future land degradation and to improve food security in Zimbabwe, particularly in the resettlement areas. In the last chapter, the same three villages in NE Zimbabwe were sampled to determine the feasibility of integrating mid-infrared spectroscopy (MIRS) and geostatistics, as a way of facilitating landscape analysis and monitoring. A nested non-aligned design with hierarchical grids of 750, 150 and 30 m resulted in 432 sampling points across all villages. At each point, a composite topsoil sample was taken and analyzed by MIRS. Conventional laboratory analyses on 25-38% of the samples were used for the prediction of concentration values on the remaining samples through the application of MIRS - partial least squares regression models. Models were successful (R2≥0.89) for sand, clay, pH, total C and N, exchangeable Ca, Mg and effective CEC; but not for silt, available P, and exchangeable K and Al (R20.82). Minimum sample sizes required to accurately estimate the mean of each soil property in each village were calculated. With regard to locations, fewer samples were needed in the new resettlement area than in the other two areas; regarding parameters, least samples were needed for estimating pH and sand. Spatial analyses of soil properties in each village were undertaken by constructing standardized isotropic semivariograms, which were usually well described by spherical models. Spatial autocorrelation of most variables was displayed over ranges of 250-695 m. The nugget-to-sill ratios showed that overall spatial dependence of soil properties was: new resettlement > old resettlement > communal area; which was attributed to both intrinsic (e.g. texture) and extrinsic (e.g. management) factors. As a new approach, geostatistical analysis was performed directly using MIRS data, after principal component analyses, where the first three components explained 70% of the overall variability. Semivariograms based on these components showed that spatial dependence per village was similar to overall dependence identified from individual soil properties in each area. The first component (explaining 49% of variation) related well with all soil properties of reference samples (absolute correlation values of 0.55-0.96). This demonstrated that MIRS data could be directly linked to geostatistics for a broad and quick evaluation of soil spatial variability. Integrating MIRS with geostatistical analyses is a cost-effective promising approach, i.e. for soil fertility and carbon sequestration assessments, mapping and monitoring at landscape level.
Investigating the mode of action of the mycoherbicide component Fusarium oxysporum f.sp. strigae on Striga parasitizing sorghum and its implication for Striga control in Africa
(2011) Ndambi Beninweck, Endah; Cadisch, Georg
Amongst the factors that are a threat to food security in Africa, is the parasitic weed Striga hermonthica which affects mostly cereals that constitute the staple food for subsistence farmers, thus affecting the livelihood of millions of people. Popularly known as witchweed, attack due to S. hermonthica can completely destroy the yield of cereal crops. Efforts to combat Striga have had very limited success since farmers rarely adopt control methods due to the mismatch between technologies and farmers? socio-economic conditions. Being such a severe problem, an appropriated method for Striga management adapted for African farmers is very much needed. The use of soil-borne fungi for biocontrol is now being developed as an alternative to the use of chemicals considering the specificity of such fungi and the fact that most of the damage by Striga is done before its emergence. The fungus Fusarium oxysporum f.sp. strigae has been identified and shown to be effective and specific to S. hermonthica and S. asiatica but its mode of action is not yet well known. It is required that the mechanisms underlying the mycoparasitic process of this natural antagonistic agent be well understood before its use. Thus, studies on the effectiveness, specificity and timely colonization of Foxy 2 on S. hermonthica are necessary as well as studies on the effect of Foxy 2 in Striga-host plants which should demonstrate its non-pathogenicity to food crops. The objective of this study was therefore to investigate the mode of action of Foxy 2 in its target S. hermonthica and non-target Sorghum bicolor and also to examine the safety of the use of this mycoherbicide by evaluating its ability to produce toxins. In the first part of the thesis, the ability of Foxy 2 to colonize sorghum roots and possibly shoots was investigated using light and transmission electron microscopy. The efficacy of Foxy 2 to cause death of S. hermonthica seedlings attached to Foxy 2 colonized sorghum roots was also evaluated. Microscopic investigations revealed that the intensity of root colonization by Foxy 2 increased with time and Foxy 2 could survive and colonize the sorghum rhizodermis, root hairs and cortical parenchyma up to four weeks after sowing. This behaviour is well adapted for Striga control as it corresponds to the peak of Striga seedling attachment. Hyphae were completely absent from the sorghum root central cylinder even after four weeks and also absent from the sorghum shoots up to 11 weeks after sowing indicating the non-pathogenity of Foxy 2 to sorghum. Furthermore, Foxy 2 was effective in controlling S. hermonthica by causing disease in 95% and 86% of S. hermonthica seedlings when coated on seeds of tolerant and susceptible sorghum cultivars respectively. Therefore, Foxy 2 could be combined with the tolerant sorghum variety in an integrated approach against S. hermonthica and S. asiatica. The effect of Foxy 2 on various growth stages of S. hermonthica was investigated subsequently so as to understand the mechanisms of action of Foxy 2 within S. hermonthica in the real living complex between the mycoherbicide Foxy 2, the parasite S. hermonthica and its host sorghum. Light, scanning and transmission electron microscopy were used to evaluate the pattern of colonization and control of S. hermonthica seedlings and shoots by Foxy 2. Results showed that 26 days after sowing Foxy 2 coated sorghum seeds, all tissues of the young S. hermonthica seedlings attached to sorghum roots were completely degraded and destroyed by Foxy 2 including the haustorial intrusive cells, hyaline tissue, vessels, central xylem elements and Striga cortical parenchyma. Some S. hermonthica plants which attached to areas of the sorghum root which were not yet colonized by Foxy 2 (towards the root tips), were able to outgrow the fungus and emerged. In the emerged S. hermonthica shoots, hyphae had subsequently penetrated and colonized vessels clogging them over long distances and were identified up to the top of the plants. In some vessels there was an intensive blockage of the vessels by hyphae such that spaces or gaps were rare. Ultrathin sections showed that the diseased S. hermonthica shoots reacted to Foxy 2 invasion by forming an electron dense wall coating along the secondary vessel walls probably to prevent fungal digestion of the walls. The study thus identified two mechanisms by which Foxy 2 contributed to wilting and death of S. hermonthica which included complete digestion of underground S. hermonthica seedlings and hyphal clogging of vessels in emerged S. hermonthica plants which interfered with water conduction. In order to understand the reactions of sorghum towards the presence of Foxy 2 as part of the risk assessment to ensure the safe use of this biocontrol agent, the action of Foxy 2 and a known pathogenic Fusarium species, F. proliferation, were compared in the fourth chapter. Sorghum roots were also wounded to expose the vascular system so as to investigate whether removal of the endodermal barrier could give access to Foxy 2 into the vessels which could lead to digestion resulting in wilting of the sorghum plants. The colonization processes of the two Fusaria species were quite different at all stages of growth. While F. proliferatum degraded the endodermis, invaded the central cylinder and digested the xylem parenchyma two weeks after sowing, Foxy 2 was restricted to the cortex even up to four weeks after sowing. Hyphae of Foxy 2 filled the intercellular spaces at the outer endodermal wall but could not penetrate the endodermis. Sorghum roots were observed to react to Foxy 2 invasion by reinforcing the central cylinder as seen by an increase in blue auto fluorescence especially of the endodermis. Five days after wounding and inoculating sorghum roots, Foxy 2 hyphae invaded the central cylinder very close to the cut but were completely absent from the central cylinder at a distance of 3000 µm from the cut, meanwhile F. proliferatum hyphae had digested the cells of the central cylinder at this distance. This indicated that not only the endodermis was a barrier but there could also be a physiological barrier within the central cylinder of the sorghum root which did not allow further spread of Foxy 2. Hence, exposure of the vascular system did not serve as a route for the invasion of Foxy 2 which therefore implied that it could not cause wilting of the plant. In the last part of the thesis, S. hermonthica shoots were analyzed by HPLC-MS/MS to investigate the possible production of toxins by Foxy 2 to kill the plant. Amongst the toxins tested (beauvericin, fumonisins B1, B2, B3, C and P series, enniatins A, A1, B and B1, and moniliformin), only beauvericin (BEA) was detected to be produced by Foxy 2 in S. hermonthica shoots. The concentration of this toxin increased with increased infection e.g. 60 µg BEA/kg Striga shoot tissue (dry weight) were detected three weeks after emergence rising to 720 µg BEA/kg Striga shoot tissue after six weeks in the severely diseased S. hermonthica shoots. When beauvericin was applied on S. hermonthica shoots at concentrations of 50 µM, transmission electron microscopy showed that all cell types became necrotic. However, beauvericin as well as all the other toxins were not detected in sorghum grains harvested from sorghum plants which were hosts to the S. hermonthica plants and growing from Foxy 2 coated sorghum seeds. Given that some F. oxysporum strains were previously shown to be able to produce fumonisins which are among the toxins which have been reported to be of potential risks to human and animal health, a pure culture of Foxy 2 was evaluated for its fumonisin production ability. Results from real-time PCR using two specific primer pairs for the FUM1 gene (which is the key gene for fumonisin synthesis), were negative confirming that Foxy 2 was not able to produce fumonisins and might not be of major concern for human and animal health when used as a biocontrol agent in the field, therefore safe for use as a biocontrol agent. To conclude, Foxy 2 showed potential to control S. hermonthica by completely destroying young underground stages and clogging vessels in aboveground stages, as well as producing the toxin beauvericin, both actions contributing to wilting of the plants. Its non-pathogenicity to sorghum and its inability to produce fumonisins could be seen as factors which make it well suited as a biocontrol agent. Further research needs to be done to evaluate its efficacy under field conditions and the impact of naturally occurring soil microorganisms and abiotic conditions on performance of Foxy 2 so as to understand its interactions with the environment and to optimize its efficacy.
Developing a biodiversity evaluation tool and scenario design methods for the Greater Mekong Subregion
(2011) Cotter, Marc; Sauerborn, Joachim
The Xishuangbanna Prefecture in Yunnan Province (PR China) is facing increasing conflicts between rural development and nature conservation because of an ongoing expansion and commercialization of farming. The rapid development of large-scale farming and the improvement of infrastructure throughout the region are posing serious threats to the conservation of endemic species of flora and fauna, while also offering possibilities for enhancing the livelihood of rural populations to an extend never seen before. The expansion of rubber (Hevea brasiliensis Willd Ex A. Juss) has caused a reduction and fragmentation of natural and secondary forest cover, thereby decreasing structural and species diversity as well as the loss of valuable ecosystem services. The establishment of intensified agriculture, especially plantations on sloping terrain, often leads to an increased erosion risk, nutrient run-off and sedimentation in water courses. Thus, large scale deforestation is not just a problem for nature conservation but also one for the rural economies. Rural development and simultaneous environment conservation often face trade-offs, especially in regions that host an exceptionally high biodiversity, such as many tropical areas. In order to adequately consider and evaluate these interactions, tools and methods have to be developed that allow decision makers to assess the impacts of different management and infrastructure options on the environment. The aim of the work presented in this thesis was to analyze and evaluate the effect of large-scale rubber cultivation on local and regional biodiversity by developing methods to integrate field studies from various disciplines into a comprehensive assessment model. This model was then used to highlight key aspects of anthropogenic influence on the plant species composition within the research area and to identify possible impacts of alternative land use decisions. Furthermore, the development of an interdisciplinary approach to scientific scenario design methods has been supplemented with a study on the acceptance of 3D-visualization as communication tool for land use planning in the background of nature conservation sciences. In order to achieve this, an overview of the agronomical and ecological aspects of rubber cultivation was provided. Literature sources referring to the impact of different cultivation systems on natural biodiversity were discussed and an introduction to the effect of rubber cultivation on Ecosystem Services was given. A method for projection of regionally adapted carbon capture properties of rubber cultivation under suboptimal growth conditions was presented and a comparative assessment of greenhouse gas emissions during the establishment of rubber plantations in regard to the preexisting vegetation was made. A biodiversity evaluation tool based on the combination of approaches from landscape ecology and empirical data within a Geographic Information System was developed. Detailed data on plant species diversity and distribution were combined with quality criteria like endemism or invasiveness to form spatially explicit biodiversity indices for different land use types in various elevation classes. Up-scaling in accordance to the land use distribution observed allowed the estimation of overall plant diversity and the evaluation of the effect of possible future land use scenarios. Habitat characteristics and spatial distribution were included into the analysis of the land use map derived from remote sensing information to allow for the assessment of fragmentation and landscape matrix structure. The methodology was tested with an array of possible present and future land use maps. It was possible not only to evaluate the different land use classes within and their distribution throughout the research area, but we were also able to compare distinct sub-regions based on topography or administrative status. The challenges stakeholders and nature conservation face in the different elevation zones of Nabanhe were highlighted and related to the findings of our partner workgroups from economy and social sciences. The feasibility of this approach to administration staff with limited experience in ecological modeling was one of the main goals in designing the methods. Given a reasonable data set on species diversity and distribution within any given tropical research area, this approach will enable planners and nature park administration to quickly project possible consequences on species diversity indices deriving from land use change within their respective research area. Using this approach, the importance of natural tropical forests for the maintenance of species diversity in tropical cultivated landscapes was highlighted. With the information gained from constructing this evaluation tool, the design and development process for a land use scenario based on the integration of multidisciplinary assessments and iterative scenario refinement with repeated stakeholder inclusion was promoted. By combining stricter conservation rules with alternative sources of income for the rural population in order to offer an alternative to monoculture rubber farming, the economic models and the land use allocation model predicted a stop in rubber and agriculture related deforestation, and the establishment of a considerable amount of reforested area. This was achieved by introducing an innovative land use type that is closely related to traditional local home garden agroforestry systems. By coupling reforestation efforts with the economic gain derived from intercropping Traditional Chinese Medicinal plants into degraded secondary forests, this scenario was, at least theoretically, able to remove deforestation pressure from the natural forest types and to offer an economic alternative to rubber cultivation. The methods used for this assignment can serve as guideline for future projects that want to implement scenario design procedures based on the combination of social sciences, economics, ecology and landscape planning. The acceptance and comprehensibility of computer based 3D visualization models for the communication of possible future land use scenarios was also tested. Two alternative scenarios were visualized and compared to the status quo, with questionnaires and guided interviews covering the acceptability and adaptability of such techniques for professionals from various fields of nature conservation. This thesis presents an overview over agronomic, economic and ecological aspects of rubber cultivation and highlights its implications on biodiversity and nature conservation. The methods discussed here can serve as a guideline for the integration of ecological indicators in land use planning and decision making processes. Although the concepts and topics introduced herein are closely interlinked within the framework of the Living Landscapes China (LILAC) research project, the methods and approaches can easily be applied to other areas in the Greater Mekong Subregion and beyond, be it the expansion of oil palm plantations in the Malayan Archipelago or the fragmentation of forests due to increased population pressure in Central Africa. Nature conservation is facing similar problems all over the developing world, and adaptable approaches such as the ones presented here are needed to support decision making processes in order to secure the preservation and long-term survival of the worlds? diversity in species and natural habitats.
Animal-plant-interactions at different scales in changing tropical landscapes of southern Yunnan, China
(2012) Meng, Ling-Zeng; Martin, Konrad
Carabid beetles (Coleoptera: Carabidae) have widely been used to assess biodiversity values of different habitats in cultivated landscapes, but rarely in the humid tropics. This study aimed to investigate effects of land use change on the carabid assemblages in a tributary valley of the Mekong River in tropical southern Yunnan, China. The study area includes habitats of traditional land use systems (rice production and shifting cultivation successions) and was dominated by natural forests until about 30 years ago. Since then, large areas of forest have been, and still are, successively transformed into commercial rubber monoculture plantations. In total, 102 species of Carabidae (including Cicindelinae) were recorded from 13 sites over different seasons, using pitfall traps, Malaise traps and aerial collectors in trees. Cluster analysis and indicator species analysis showed that three types of habitat (rice field fallows, early natural successions and natural forest) possess a degree of uniqueness in species composition. Non-metric multidimensional scaling revealed that the environmental factors explaining 80% of the total variation in carabid assemblage composition are the degree of vegetational openness of a habitat and its plant species diversity. Rice field fallows had significantly higher numbers of species and individuals than any other type of habitat and are probably dominated by species originating from other regions. Carabid assemblages of young rubber plantations (5 and 8 years) were quantitatively similar to those of forests, but without species of significant indicator value. With increasing plantation age (20 and 40 years), the number of carabid species decreased. Increasing age and a further spatial expansion of rubber plantations at the expense of forest areas will have negative impacts on the native forest carabid assemblages with strongest effects on forest specialists and rare species.
Ecophysiological and agronomic response of Abaca (Musa textilis) to different resource conditions in Leyte Island, Philippines
(2012) Bande, Marlito M.; Sauerborn, Joachim
Abaca (Musa textilis Née) is closely related to edible bananas (Musa acuminata Colla and M. balbisiana Colla). Abaca usually thrives in the shade beneath tall trees, especially important for protecting the young plants from the sun and the older, taller plants from wind breakage. However, there is still disagreement on the need for shade trees in abaca cultivation. Hence, this study was conducted to ascertain the ecophysiological and agronomic response of abaca grown in different shade conditions, water and nutrient management systems in Leyte Island, Philippines. The objectives of the study were to: (a) explore the influence of shade and irrigation-fertilization on the morphological and physiological performance of abaca; (b) investigate the effect of reducing light intensities by 30%, 40% and 50% of full sunlight on fiber yield and fiber quality; (c) determine the optimum light requirement of abaca plants to attain the optimum yield without affecting the quality of the fiber for industrial use; (d) examine the effect of shade and irrigation-fertilization on biomass production and allocation as well as on NPK absorption and distribution among abaca organs; and (e) find out if irrigation and fertilization could offset the effect of shade on biomass production, NPK absorption and fiber yield of abaca. Field trials were established where light infiltration was reduced by 30%, 40%, and 50% of full sunlight using polypropylene shade nets. Irrigation was applied at a rate of 5 liters plant-1 application-1 day-1. The frequency of irrigation was applied two times per day at seedling stage (1-3 months after planting), three times at the early vegetative stage (4-6 MAP), four times at the late vegetative stage (7-9 MAP), and five times at flagleaf stage (10-12 MAP). On the other hand, placement application of N, P2O5, K2O using complete fertilizer was done at 14 g plant-1 in every three months for the first six months and was increased to 40 g plant-1 in every three months for the next six months after planting. The results of this study showed that plant height, cumulative leaf area, pseudostem length and base girth of abaca significantly improved when the light was further reduced to 50%. The application of NPK fertilizer and combination of irrigation-fertilization further enhanced the growth performance of abaca. Statistical analysis showed that shade, NPK fertilization and combination of irrigation-fertilization positively affected dry matter production, crop growth rate, leaf area ratio and net assimilation rate from seedling to flagleaf stage. Furthermore, biomass allocation and NPK distribution among abaca organs was significantly affected by high radiation and/or temperature at seedling and early vegetative stages, and differential leaf senescence at flagleaf stage where shade plays a considerable function. The amount of NPK absorbed by each organ was influenced by the growth made during the different stages of crop development. Meanwhile, irrigation and fertilizer application further improved biomass allocation that considerably increased NPK absorption and distribution among plant parts. With regards to agronomic response, the abaca planted under different light regimes showed that 50% shade had significantly higher fiber yield compared to those that were under other light treatments since the plants pseudostem under such treatment were longer, bigger and heavier. The combination of irrigation and fertilization could further enhance fiber yield to as much as 141% (compared to the control) but this was not enough to offset the effects of shade on the physiological performance of the plant which significantly increased fiber yield to as much as 265% (compared to the control). Statistical analysis showed that shade and irrigation-fertilizer application had no significant effect on fiber fineness and tensile strength. The superior productivity of abaca in response to shade was due to the avoidance of photoinhibition and photooxidative damage that negatively affected the abaca grown under full sunlight at seedling and early vegetative stage. Likewise, the detrimental effect of photoinhibition on the photosynthetic capacity of abaca grown in full sunlight significantly decreased biomass production and allocation among abaca organs. The amount of NPK absorbed by each organ was influenced by high radiation causing photooxidative damage at seedling stage and differential leaf senescence at flagleaf stage. This significantly affected the pattern of biomass allocation and NPK distribution among abaca plant organs. On the other hand, the application of fertilizer considerably enhanced biomass production but did not change the usual pattern of biomass and NPK distribution. The results showed that irrigation and fertilizer application cannot offset or equalize the positive effect of shade on the vegetative growth, physiological performance, and NPK absorption among plant organs.
Physiological and growth responses of Jatropha curca L. to water, nitrogen and salt stresses
(2012) Rajaona, Arisoa Mampionona; Asch, Folkard
This thesis provides necessary and complementary information for an improved understanding of jatropha growth to guide further research to evaluate the response of jatropha to abiotic stressors and for designing plantations adapted to the plants? requirements. Given the fact that jatropha is claimed to grow on marginal lands, we studied effects of water supply, salt stress, nitrogen and air humidity as major abiotic stressors on gas exchange parameters and biomass production followed by management options for pruning the trees to positively influence biomass productivity and to contribute to optimize resource use. The effects of water availability (rainfed versus irrigated) on growth and gas exchange parameters were investigated for 4-year old jatropha grown in a semi-arid environment at a plantation site in Madagascar in 2010. The results confirmed that 1250 mm water in addition to a 500 mm rainfall did not affect biomass production and instantaneous gas exchange. Nevertheless, leaf light responses of irrigated plants were higher than that of rainfed plants. The study showed to what extent salt stress affected water use, canopy water vapour conductance, leaf growth and Na and K concentrations of leaves of 3-year old and young jatropha plants. 3-year old plants were exposed to seven salt levels (0-300 mmol NaCl L-1) during 20 days and young plants to five salt levels (0-200 mmol NaCl L-1) during 6 days. In both experiments, plants responded rapidly to salt stress by reducing water loss. The threshold value of responses was between 0 and 5 dS m-1. Leaf area increment of young jatropha had a threshold value of 5 dS m-1 implying that jatropha is sensitive to external salt application in terms of canopy development, conductance and CO2 assimilation rate. Transpiration of plants in both experiments was reduced to 55% at EC values between 11 and 12 dS m-1 as compared to non-stressed plants. These findings indicate that jatropha responds sensitive to salt stress in terms of leaf elongation rate and consequently canopy development, and to immediate physiological responses. Leaf gas exchange characteristics of jatropha as affected by nitrogen supply and leaf age were intensively studied, as carbon assimilation is one of the central processes of plant growth and consequently a key process embedded in modelling approaches of plant productivity. This study showed that N supply effects on leaf gas exchange of jatropha leaves were small with only the treatment without nitrogen resulting in lower rates of CO2 assimilation rate and light saturated CO2 assimilation rate, nevertheless, effects of N supply on biomass formation were pronounced. Instantaneous rates of leaf gas exchange of different leaves subject to variable air humidity (atmospheric vapour pressure deficit (VPD)) were investigated. This study showed that CO2 assimilation rate (A) and stomatal conductance (gs) were correlated in a hyperbolic fashion, and that gs declined with increasing VPD. Maximal stomatal conductance of jatropha was in the range of 382 mmol m-2 s-1 and gs is predicted to be close to zero at 6 kPa. Effects of VPD, via stomatal conductance, by preventing high transpiration rates, have been demonstrated to be decisive on water use efficiency. Our findings are in this regard relevant for the estimation of water use efficiency of jatropha. The outcome further indicates favourable conditions at which stomatal opening is high and thereby allowing for biomass formation. This information should be considered in approaches which aim at quantifying leaf activity of field-grown bushes which are characterized by spatially highly diverse conditions in terms of microclimatic parameters. Microclimatic parameters can be modified by the tree structure. The reported field experiment on 4-year old jatropha indicated that the biomass production and canopy size depended mainly on primary branch length. A comparison of plants of different pruning types with regard to trunk height (43 versus 29 cm) and total length of primary branches (171 versus 310 cm), suggest that higher biomass production and greater leaf area projection was realized by trees with short trunks and long primary branches. Growth of twigs and leaves was positively correlated with total length of branches. Relative dry mass allocation to branches, twigs and leaves, length of twigs per cm of branches and specific leaf area were not affected by pruning and water supply. Trees with shorter branches had a higher leaf area density. As opposed to an allometric relationship between the average diameter of primary branches and total above ground biomass, our data suggest that these traits were not constantly correlated. Our data indicate that the length of newly formed twigs, where the leaves are attached to, can be related to the total length of already established branches. Leaf area density and relative dry mass allocation to leaves were not affected by the two pruning techniques, indicating that pruning differences in leaf area size were proportionally converted to corresponding pruning differences in the canopy volume exploited by plants. The results reported in this study are relevant for understanding jatropha growth. It helps farmers first for a better plantation management and researchers as well as contribution to future modelling purpose concerning jatropha growth under variable climatic conditions. Additionally, it should complement information for a better set of priorities in research, contribute indirectly to breeding programs and adjust agricultural policies in terms of encountering global change.
Genotypic responses of upland rice to an altitudinal gradient
(2012) Shrestha, Suchit Prasad; Asch, Folkard
Adaptation strategies are required for crops to cope with changing climate. The impact of climate change on crop production is not straight forward to predict as extreme events comprise multiple combination of abiotic stresses and their impact differs in crop physiological growth stages. The mechanism on how new abiotic stress combinations translate into phenology and yield, and which cultivars are better adapted is yet unclear. Crop growth models are available that have been parameterized and validated for some aspects of possible climate change scenarios but in view of complex interactions crop responses to climate change are difficult to predict. On the other hand, prediction of the complex ideotype trait combinations may be interesting for breeders but physiological models are required that are well validated for the target environments. In upland rice grown under rainfed conditions without surface water accumulation methane emission is negligible and therefore greenhouse gas emission much lower compared to irrigated paddy rice systems. In addition, growing demand for rice and the increasing pressure on irrigated land leads to development of upland rice areas to supplement irrigated rice. Therefore, this study investigates genetically diverse upland rice genotypes from a wide range of origins across altitudinal gradient locations. The main objective of this study is to investigate genotypic responses of upland rice to different environments in order to calibrate crop growth models, which allow the evaluation of effects of climate change on upland rice systems. Multi-locational field (three locations: 1625, 965 and 25 m asl) trials comprising non-replicated phenological plots with five sowing dates (monthly staggered) in two consecutive years creating thirty different environments, and replicated physiological yield trials with two sowing dates (monthly staggered; early and late sowing) in two consecutive years creating twelve different environments were established in Madagascar. Ten contrasting upland rice genotypes were included in both field trials. Meteorological data were recorded on a daily basis during trial periods. Developmental stages were observed in the phenological plots; in the physiological plots yield and yield components were recorded. In addition, greenhouse trials were conducted with one upland rice genotype subjected to seven N-supply levels in a hydroponic system at the University of Hohenheim in order to understand the relationship between chlorophyll index, photochemical reflectance index and chlorophyll fluorescence parameters. Various statistical tools were applied to analyse field and greenhouse data sets. The phenological trial showed that duration to flowering was 117, 81 and 67 d in high (HA), mid (MA) and low (LA) altitudinal locations respectively. 90% of the total variance was explained by location when pooled over genotype, location, sowing dates and year. In HA, factors such as genotype, sowing date and year equally contributed to the observed variability whereas in MA year was the most determining factor and genotype had no significant contribution. Similarly, in LA sowing date was the main influencing factor and year had no significant effect. Aggregated data over locations, sowing dates and years indicated that each degree Celsius rise in mean air temperature decreased crop duration by 5 to 9 days depending upon genotype. Basic genotypic thermal constants Tbase ranged from 9.8 to 13.9 °C and Tsum from 816 to 1220 °C d within the selected genotypes. Cold tolerant genotypes were less affected by lower Tmin (14 °C) at booting to heading stage regarding spikelet sterility in HA, whereas others were highly affected at 15 °C (cold stress). Similarly, both cold sensitive and tolerant genotypes were affected by Tmax (above 30 °C) at flowering in MA and LA locations (heat stress). Grain yield and yield components were highly affected by location, year, sowing date, and genotypes and the interactions between these yield-determining factors were obvious. In HA, early sown cold tolerant genotypes had more than 5 t ha-1 grain yield and one month delay in sowing led to highly reduced yield whereas other genotypes had very poor yield on both sowing dates due to cold stress. In MA, yield difference between sowing date and genotypes was small (4.3 - 4.9 t ha-1). Grain yield in LA was vulnerable due to frequent tropical storms. Yield stability analysis showed that cold tolerant genotypes had above average stability. AMMI model for grain yield showed that environment and genotype by environment interactions were highly significant. Yield components determined during specific development stages of the genotype such as tillers per hill and percentage of filled spikelets were mainly influenced by environment, spikelets per panicle and thousand grain weight were influenced by genotype, and percentage of productive tillers was equally influenced by both genotype and environment. PCA biplots showed that all HA environments were equally influenced by all weather parameters with minimum air temperature having the strongest positive influence on genotypic performance. In all MA environments genotypic performance in all phenophases was strongly and positively influenced by rainfall, and strongly and negatively influenced by vapour pressure deficit, solar radiation and potential evapotranspiration. In the LA environments, main weather parameters influencing genotypic performance were maximum temperature and high rainfall accompanied by strong winds. The field measured SPAD values of the upper canopy leaves reflected the location specific N-remobilization and leaf senescence levels after flowering. Similarly, PRI values showed the abiotic stress responses among development stages and locations along the altitudinal gradient. These readings showed that genotypes were efficient in radiation use and N-remobilization after flowering in MA. The unsynchronized relationship between source (leaf) and sink (grain) explained the yield penalty. Emphasis on identification of morpho-physiological traits contributing to cold tolerance should be placed for further breeding. We conclude that genotypic responses of upland rice cultivars differed across altitudinal gradients. Genotypes that are well adapted in HA can easily be adapted in MA without yield decrease. But genotypes well adapted in MA may show a huge yield penalty in HA due to lower temperature during reproductive phase and consequently reduced sink formation. Frequent tropical storms and high temperature reduced yield potential in LA. Therefore, HA has a large potential for the future food security considering climate change scenarios. At present, MA is favorable for upland rice production systems, whereas LA is highly vulnerable and is expected to be even more vulnerable in future. Those results on genotype-specific responses to environmental conditions allow further improvement of crop models such as RIDEV and SAMARA (synthesis of SARRAH and EcoMeristem), which can be used to test a number of phenotypic traits x environments combinations to define ideotypes of upland rice varieties adapted to changing climate and cropping calendars. Genotypic responses of phyllochron, biomass production and crop growth rate, and radiation use efficiency across altitudinal gradients will be included to parameterize these models. In this regard, collaborations with AfricaRice, CIRAD and IRRI are ongoing.
Agrobiodiversity and its use in Naban River Watershed National Nature Reserve : implications for bio-cultural diversity conservation
(2012) Ghorbani Dahaneh, Abdolbaset; Sauerborn, Joachim
This study was conducted in the Naban River Watershed National Nature Reserve (NRWNNR), Xishuangbanna Dai Prefecture, SW China and aimed at identifying the diversity of medicinal and food plants used by local people living in NRWNNR and documenting their applications. NRWNNR is diverse biologically and culturally and people living in its territories get benefits from their diverse natural environment. However the extension of cash crops such as rubber (Hevea brasilliens (Willd. ex A. Juss.) Müll. Arg.) plantations and fragmentation of natural habitats including forests resulted in decreasing biological diversity which could be used by the local people. This also put more pressure on the remaining forests and plant resources. In order to find sustainable alternatives to conserve biodiversity and at the same time helping the development of the area it is necessary to know the available resources in the area. Among important plant resources in the area are non-timber forest products with economic and cultural importance including medicinal and food plants. Therefore, using ethnobotanical methods this study intended to document wild medicinal and food plant resources used by ethnic groups and their use details including their collection practices, preparation methods and habitat preferences. Data on useful plant resources was used to identify the main land use sources of useful plants for local people. The study also intended to understand the role of these plants in local people?s livelihood by identifying economically important medicinal and food plants traded in the area. Vulnerability of plant species to resource exploitation and harvest sustainability for selected species were assessed. To achieve above mentioned objectives, an ethnobotanical inventory of useful wild plant resources was conducted in the area to collect data on wild plant resources and uses. Semi-structured, freelisting, and household interviews were conducted from January 2008 to January 2010. Informants from Dai, Hani, Lahu and Mountain Han ethnic groups were selected randomly for freelisting and semi-structured interviews and key informants by the snowball method. Household interviews were conducted in six villages. Interviews were also conducted with harvesters and traders. All interviews were supplemented with plant sample collection for botanical identification. Plant specimens were prepared, dried, and identified with the help of local botanists. To address the vulnerability and sustainability of plant harvest, strip-transects were used to estimate the density and distribution of selected species in natural populations. Results showed that 480 plant species (25% of recorded flora) from 117 families and 334 genera are used by the local population. From these, 378 species (19%) belonging to 102 families and 277 genera are used as medicine and 161 species (8%) representing 68 families and 116 genera are used as food plants. Concerning livelihood contribution, most of these plants are used at the subsistence level and not for income generation. However some households can get from 1.1% up to 25.4% of their total annual income from sale of few medicinal species. Among food plants only bamboo shoots and mushrooms contribute to the cash income of households with the highest share in BenGang Hani village (1.1%). Knowledge of medicinal plant use and folk medicine still exists in the area and there are local healers and practitioners who are active in some villages. However this knowledge shows some differences among ethnic groups. Number of medicinal plants used by Lahu and Hani is different and some species are solely known and used by only one ethnic group. Since these ethnic groups live in neighboring villages, it was expected that a large proportion of their medicinal plant knowledge is shared. However, the diversity of medicinal species utilized by the two ethnic groups show 30% overlap. Medicinal plants are grouped into different categories based on frequency of use. 1- Frequently used medicinal plants which are few in number. 2- A large number of medicinal species are only known and collected by traditional healers or some knowledgeable elderly people. 3- A few numbers of medicinal plants are frequently and in high amounts harvested by locale people for commercial purposes and not for self consumption. Examples of these species include Asparagus subscandens F.T. Wang & S.C. Chen, Asparagus filicinus Buch.-Ham. ex D. Don, Stemona tuberosa Lour. and Paris polyphylla var. yunnanensis (Franch) Hand -Mazz. Although use of these medicinal plants is known to traditional healers, majority of the villagers which are involved in harvesting of these species are not knowledgeable about their medicinal applications. In fact harvest is driven by market demand which is brought to the area by middlemen and retailers visiting the villages. Wild food plants are also grouped based on harvest and use frequency into different categories. The first group includes species with high frequency of use which have a very common distribution range in the area. Second group includes bamboo shoots and mushrooms which are traded to some extent. The last group includes a large number of species which are not used frequently but are potential food plants used only by a small proportion of the local population or during famine or crop failure periods. Based on vulnerability assessment of marketed species in the area, most of the important plants are in danger of overexploitation. However frequently used food plants are not threatened with overharvesting since they are very common in the area. Among the wild food resources bamboo shoots and mushrooms are exploited without sustainability measures. Collection of high economically valuable medicinal plants is also not sustainable as subterranean parts are harvested and collection is fatal for the plant. Sustainable harvest and management strategies should be implemented to prevent overexploitation of these species. Findings also highlight plant species which can be proper candidates for cultivation especially in agroforestry systems. There is already a good potential on the improvement of economic gains from some forest products such as mushrooms with value adding by improving drying methods and establishment of village based enterprises. Cultivation of economically important medicinal plants in herbal gardens or agroforestry systems are recommended since it can reduce pressure on natural population and at the same time diversify and secure the economic gain of villagers.
Human urine as a crop fertilizer under saline conditions
(2013) Boh, Michael Yongha; Sauerborn, Joachim
Soil salinity and nutrients deficiency are jointly responsible for low agricultural production in many parts of the world. With a still growing world population and a continuing pressure on arable land, there is need to increase the productivity of salt affected soils. It is known that the application of N fertilizer can mitigate the deleterious effects of salinity on crop growth but this beneficial effect depends on the source of nitrogen and the extent of soil salinity. Whereas commercial inorganic fertilizers are expensive and often inaccessible to poor farmers especially in developing countries, human urine is an alternative low-cost fertilizer which, if collected and used, can replace up to 20% of current world fertilizer consumption. Its efficacy to increase crop productivity has been validated in scientific experiments. However, the high concentration of soluble salts (especially Na and Cl) in urine may impose a restriction on its use under saline and/or sodic conditions. The research presented in this thesis investigates the extent to which urine can be used as a fertilizer under saline/sodic conditions. It compares the effect of urine and ammonium nitrate-N sources on nutrients accumulation and growth of maize and sorghum plants in NaCl-saline substrate under controlled environmental conditions. Additionally, the effect of urine fertilization on changes in substrate chemical composition was investigated. Due to the high content of K, Ca and Mg in wood ash which can improve the soil cationic balance in salt affected soils, it was further investigated whether or not supplemental wood ash application can enhance salt- and Na-tolerance of urine-fertilized maize plants. Regardless of NaCl salinity treatment, no significant difference in investigated growth factors (height, leaf area and shoot biomass accumulation) of maize plants was measured when N was supplied at 180 mg kg-1 cultivation substrate as urine or ammonium nitrate. Meanwhile, urine treated maize plants produced comparatively less shoot biomass following the application of 380 mg N kg-1 of cultivation substrate and at NaCl salinities of 4.6 and 7.6 dS m-1. As expected, sorghum plants were more tolerant to salinity than maize and produced more biomass under urine than ammonium nitrate fertilization. Though there was a positive relationship between biomass yield and tissue nitrogen concentration regardless of salinity treatment level, this relationship was stronger for ammonium nitrate than urine treatments. Ca and Mg concentration in the tissue of urine-fed maize and sorghum plants was higher than those treated with ammonium nitrate which can be explained by the inherent content of these nutrients in urine. However, there was no direct relationship with biomass yield of maize plants of either nutrient. Additionally, urine fertilization significantly increased substrate salinity by 2 to 3-fold. Substrate sodium concentration and a tendency towards mounting sodicity with an increase in urine fertilization were also observed. At a NaCl-salinity of ECe 4.2 dS m-1, the application of wood ash (150 mg kg-1 soil) alone or in combination with 75 mg urine-N kg-1 soil fostered Na and salinity tolerance of maize which can be explained by the dilution effect of K and Ca supplied through wood ash. However, at a higher urine-N dosage (150 mg kg-1 soil) with or without wood ash enrichment growth inhibition occurred indicating that the tolerance threshold had been exceeded assumingly due to urine-induced increase in Na and salinity. It was demonstrated that urine can substitute ammonium nitrate as a source of nitrogen for maize and sorghum and can be considered for fertilization if salinity does not exceed ECe 4.0 dS m-1. Due to urine-induced increase in salinity and Na concentration in the growing medium, regular monitoring for salt build up and the use of salt-tolerant crop varieties should be included in urine fertilizer planning. It was further demonstrated that supplemental wood ash enhances Na and salinity tolerance and where necessary should be incorporated in urine-fertilizer programs.
Environmental effects on physical properties of Geohumus and effects of its application on drought responses in maize
(2013) Duong, Van Nha; Asch, Folkard
Geohumus belongs to a new generation of soil melioration/hydrophilic polymers; however, evidence is limited with regard to both, the ability of Geohumus to store water in variable abiotic environments and the effects of Geohumus or other hydrophilic polymers on plant genotypes in response to drought condition. Therefore, this study aims at providing necessary and complementary information for improving Geohumus usage under field condition, and to improve our ecophysiological understanding of the interactions between Geohumus, plant genotype and the growing environment. Three series of experiments were conducted to investigate (1) how abiotic factors affect the water holding capacity and restorability of Geohumus, (2) how the application of Geohumus affects plant morphological and physiological traits in response to different irrigation scenarios such as full irrigation, water deficit, and re-watering and (3) how the application of Geohumus in different soil types affects drought induced plant root-shoot communication. Water holding capacity (WHC) and restorability of Geohumus in mL water g-1 was determined by immersing teabags with fresh and used Geohumus in prepared media under laboratory conditions. A greenhouse experiment was carried out in order to analyze morphological and physiological responses of the two maize cultivars Mikado and Companero to progressive drought or full irrigation (field capacity) as affected by Geohumus. To obtain in depth information on Geohumus-plant interactions, a split root system experiment was conducted as a tool to investigate hydraulic and bio-chemical root-shoot communication of Mikado and Companero under full irrigation, partial rootzone drying, and deficit irrigation. Our results showed a negative correlation between salt concentration and water holding capacity (WHC) of Geohumus due to replacement of water molecules by ions at the polarized sites within the polymer chain (James and Richards 1986). Furthermore, salt types affected the WHC of Geohumus differently; in particular, multivalent ions were stronger impeding Geohumus compared to monovalent ions. Consequently, Geohumus application to sandy soil with base fertilizer application or to compost could not improve soil water content. However, split fertilizer application to sandy soil containing Geohumus led to a significantly improved soil moisture content indicating that timing and amount of fertilizer should be carefully considered under Geohumus application. Furthermore, for field applications the effect of climate needs to be considered, since the WHC of Geohumus increased with increasing temperature. The preferential ion uptake of Geohumus could translate into competition with plant roots for nutrient uptake from soil solution. On the other hand, Geohumus can capture nutrients which might have been lost for plants due to drainage. We found indications of these positive effects since biomass and leaf area of Mikado and Companero maize genotypes were increased compared to soils without Geohumus. Theoretically, polymers could release stored water to plants under drought stress; which in turn could inhibit or delay chemical signaling. However, our results showed increased concentrations of [ABA]leaf and [ABA]xylem of both Mikado and Companero grown in sandy soil with Geohumus in response to drought compared to treatments without Geohumus. This hormonal response was associated with larger leaf area and greater biomass resulting in a higher plant water demand due to its increased transpiration area while Geohumus did not improve soil water content significantly. On the other, hand root/shoot ratio, absolute root length and root biomass were decreased in plants grown with Geohumus. This suggests that plants grown with Geohumus under drought conditions could not extract water from deeper soil layers. The split root experiments showed that the larger leaf area of plants grown with Geohumus in combination with limited moisture content of sandy soil resulted in a stronger chemical root-shoot signal related to water stress. Regardless the increased [ABA]xylem which is associated with a reduction of stomatal conductance, Geohumus application could result in a decreased leaf water potential under partial root zone drying. Mikado grown with and without Geohumus, as a genotype potentially adapted to drought conditions, was able (1) to maintain its water potential under water limited conditions by penetrating roots into deeper soil layers (2) to delay the expression of physiological traits associated with drought, and (3) to maintain its shoot weight in contrast to Companero, a drought sensitive cultivar. The presented results are of relevance for the improvement of our understanding of the impact of abiotic factors such as temperature, salt concentration, and salt types on the WHC of Geohumus and therefore will help to optimize the application of hydro-gels under field conditions. Beneficial traits of plant genotypes grown under Geohumus application were identified, which will be valuable for breeding and applied programs targeting at crop improvement in arid and sub-arid regions and areas vulnerable to climate change.
Development of coupled mid-infrared spectroscopic and thermal analytical approaches for the characterization and modeling of soil organic matter dynamics of arable soils
(2013) Demyan, Michael Scott; Cadisch, Georg
Soil organic matter (SOM) is a large part of the global carbon cycle both as a stock, as a source of fluxes (gaseous, dissolved, or sediments) to other stocks, and is also an important component of soil fertility and likewise plant productivity. Due to the growing need for additional data for both global studies related to climate change and soil fertility, additional information is needed not only on the total quantity of SOM, but its distribution within time and space and also its quality. In this study the use of mid-infrared spectroscopy in different applications was explored as an indicator of soil quality or composition, to measure the distribution of quality in different soils and fractions, and how these new methods could be used for SOM model parameterizations compared to other methods for both short and medium term model simulations. Firstly, certain mid-infrared active functional groups as measured with diffuse reflectance spectroscopy (DRIFTS) were studied in a long term fertilization experiment (Bad Lauchstädt) to ascertain the suitability of these different functional groups as indicators of the long term impacts of different fertilizer applications and also in various SOM fractions as separated by size-density approaches. Secondly, a coupled mid-infrared thermally evolved gas analysis was combined with in-situ monitoring of changes in vibrational functional groups to assign different qualities to different temperature ranges during a thermal oxidation experiment to 700 °C. Lastly, these two approaches were compared to traditional SOM fractionation as more rapid alternatives to parameterizing SOM pool sizes in the Century multi-compartment SOM model applied to arable soils at sites in the Kraichgau and Swabian Alb areas in Southwest Germany. In the long-term experiment (Bad Lauchstädt) it was found that certain vibrational functional groups (i.e. aliphatic (2930 1/cm) and aromatic (1620 1/cm)) in bulk soil varied (P < 0.05) according to long-term farmyard manure (FYM) and/or mineral fertilizer application. The application of 30 Mg/ha every second year of FYM increased the proportion of aliphatics as compared to aromatics, while the opposite was true for the control treatment (without any mineral and FYM fertilizer). The ratio of the aromatic to aliphatic relative peak areas were found to be positively related to the ratio of stabilized (SOC in heavy density fractions and clay size fraction) to labile SOC (light density fraction). This indicated that this peak area ratio (aromatic to aliphatic) is an indicator for the relative contribution of stabile to labile SOM as a stability index. In the next phase of the methodological development, evolved gas analysis (EGA) was used during a programmed heating of soil samples to 700°C to link EGA characteristics with SOM. An additional methodological step was the utilization of in-situ diffuse reflectance (in situT DRIFTS) measurements during heating as an indicator of the nature of SOM being decomposed at different temperatures. Thermal stability was found to be affected by experimental conditions and also sample type. The heating rate, amount of C in the sample, and volume of the sample in the heating chamber changed the rate and overall shape of the CO2 evolution curve and needed to be optimized when comparing different SOM fractions. In the long term experiment of Bad Lauchstädt, a decreasing thermal stability as measured by temperature of maximum CO2 evolution was found in the order from control > mineral fertilizer > manure > manure and mineral fertilizer. Furthermore, after a 490 day soil incubation at 20°C the thermal stability of SOC increased, but only slightly. In the in-situT DRIFTS method, the intensity of previously identified vibrational functional groups decreased (degraded) at different temperatures. The functional groups decreased in the order of aliphatic, alcoholic, and carboxylates, and at higher temperatures, also aromatic groups decreased. These findings were used as rules for fitting multiple peaks to the total evolved CO2 curve to derive SOM pools of different reactivity. Pools derived from the measured fractions of mid-infrared functional groups (aliphatic, carboxylate/aromatic, aromatic), evolved gas analysis (CO2) fitted peaks (centered at 320, 380, 540°C), and size-density fractionation (particulate organic matter, heavy density fraction, silt and clay fraction) in addition to a long-term equilibrium model run, were used to parameterize the SOM pools of the Century model as implemented in the Land Use Change Assessment tool (LUCIA) and compared to measured soil surface CO2 fluxes and soil organic carbon (SOC) contents after 2 years. The best fits for the short term study were found to be the SOM fractionation DRIFTS and EGA pool initialization methods, but the differences over two years were very small for the three different parameterization methods and generally CO2 fluxes were underestimated. A 20 year simulation, keeping all rate constants the same, on the other hand, showed large changes in both the SOC (14 Mg/ha, 0 to 30 cm) and the distribution in the pools. As compared to the 2010 baseline SOC, the DRIFTS, EGA-1, and SOM fractionation methods were closest in the Kraichgau site, while the equilibrium method was closest in the Swabian Alb. Overall, DRIFT mid-infrared spectroscopy showed its utility as a rapid assessment of the general distribution of stable to labile SOM in bulk soil. Additionally, when coupled with EGA and in-situ DRIFTS measurements, the integrated method can provide additional information during the thermal degradation of SOM during heating. All methods investigated found changes as a result of soil fertilization management, and between SOM fractions. Lastly, it was shown that such information can be used for direct SOM model inputs, although the methods should be tested on further land uses and soil types. These mid-infrared thermally coupled spectroscopic techniques represent an advance in the use of mid-infrared spectroscopy in the field of detailed SOM characterization for modeling SOM dynamics.
Prediction of soil properties for agricultural and environmental applications from infrared and X-ray soil spectral properties
(2013) Towett, Erick Kibet; Cadisch, Georg
Many of today?s most pressing problems facing developing countries, such as food security, climate change, and environmental protection, require large area data on soil functional capacity. Conventional assessments (methods and measurements) of soil capacity to perform specific agricultural and environmental functions are time consuming and expensive. In addition, repeatability, reproducibility and accuracy of conventional soil analytical data are major challenges. New, rapid methods to quantify soil properties are needed, especially in developing countries where reliable data on soil properties is sparse, and to take advantage of new opportunities for digital soil mapping. Mid infrared diffuse reflectance spectroscopy (MIR) has already shown promise as a rapid analytical tool and there are new opportunities to include other high-throughput techniques, such as total X-ray fluorescence (TXRF), and X-ray diffraction (XRD) spectroscopy. In this study TXRF and XRD were tested in conjunction with IR to provide powerful diagnostic capabilities for the direct prediction of key soil properties for agricultural and environmental applications especially for Sub-Saharan Africa (SSA) soils. Optimal combinations of spectral methods for use in pedotransfer functions for low cost, rapid prediction of chemical and physical properties of African soils as well as prediction models for soil organic carbon and soil fertility properties (soil extractable nutrients, pH and exchangeable acidity) were tested in this study. These state-of-the-art methods for large-area soil health measurement and monitoring will aid in accelerating economic development in developing sub-Saharan Africa countries with regards to climate change, increasing water scarcity and impacts on local and global food security as well as sustainable agricultural production and ecosystem resilience in the tropics. This study has developed and tested a method for the use of TXRF for direct quantification of total element concentrations in soils using a TXRF (S2 PICOFOXTM) spectrometer and demonstrated that TXRF could be used as a rapid screening tool for total element concentrations in soils assuming sufficient calibration measures are followed. The results of the current study have shown that TXRF can provide efficient chemical fingerprinting which could be further tested for inferring soil chemical and physical functional properties which is of interest in the African soil context for agricultural and environmental management at large scale. Further, this thesis has helped to improve understanding of the variation and patterns of element concentration data for 1034 soil samples from 34 stratified randomly-located 100-km2 ?sentinel? sites across SSA and explored the link between variability of soil properties and climate, parent material, vegetation types and land use patterns with the help of Random Forests statistics. Our results of total element concentration were within the range reported globally for soil Cr, Mn, Zn, Ni, V, Sr, and Y and in the high range for Al, Cu, Ta, Pb, and Ga. There were significant variations (P < 0.05) in total element composition within and between the sites for all the elements analysed. In addition, the greatest proportion of total variance and number of significant variance components occurred at the site (55-88%) followed by the cluster nested within site levels (10-40%). Our results also indicated that the strong observed within site as well as between site variations in many elements can serve to diagnose their soil fertility potential. Explorations of the relationships between element composition data and other site factors using ?randomForest? statistics have demonstrated that all site and soil-forming factors have important influence on total elemental concentrations in the soil with the most important variables explaining the main patterns of variation in total element concentrations being cluster, topography, landuse, precipitation and temperature. However, the importance of cluster can be explained by spatial correlation at distances of <1 km. This study has also analysed the potential of combining analyses undertaken using MIR spectroscopy and TXRF on 700 soil samples from 44 ?sentinel? sites distributed across SSA. MIR prediction models for soil organic carbon, and other soil fertility properties (such as soil extractable nutrients, pH, exchangeable acidity and soil texture) were developed using Random Forests (RF) regression and the current study has added total element concentration data to the residuals of the MIRS predictions to test how they can improve the MIR prediction accuracies. The RF approach out-perfomed the conventional partial least squares regression (PLSR) on simultaneous determination of soil properties; and in addition, RF results were also easily interpretable, computationally much faster and did not rely on data transformations or any other assumptions about data distributions compared to PLSR. With respect to the potential of combining TXRF and MIR spectra, including total element concentration data from TXRF analysis in the RF models significantly reduced root mean square error of prediction by 63% for Ecd, 54% for Mehlich-3 S, and 53% for Mehlich-3 Na. Thus, TXRF spectra were a useful supplement to improve prediction of soil properties not well predicted by MIRS. The prediction improvement from including TXRF was due to detection of a few outliers that did not appear as MIR spectral outliers. MIR showed remarkable ability to capture total elemental composition effects on physico-chemical soil properties but TXRF may have potential for outlier detection in large studies. This study has also helped to develop high-throughput spectral analytical methods and provided recommendations on optimal spectral analytical methods for the Globally Integrated Africa Soil Information Service (AfSIS) Project. Successfully developed methods in this study will become part of the standard AfSIS procedures.
Understanding the role of plant growth promoting bacteria on sorghum growth and biotic suppression of striga infestation
(2014) Mounde, Lenard Gichana; Sauerborn, Joachim
Witchweeds (Striga sp.) are parasitic weeds of great agricultural significance, parasitizing the roots of their hosts. Striga, like all other root parasitic weeds, drain essential organic and inorganic resources from their hosts leading to poor crop development and low yield. In Africa, about 50 million ha in over 30 countries are infested by Striga spp. causing grain loss of cereals. Estimated yield losses of maize, sorghum, millets and upland rice are between 30 and 90%. The parasite, therefore, is ranked as the leading biotic constraint to cereal production in the continent. Plant growth promoting rhizobacteria (PGPR) are promising components for integrated solutions to agro-environmental problems because inoculants possess the capacity to promote crop growth and reduce the population of deleterious microbes in the rhizosphere. Although there are numerous studies on crop growth promotion and biological control of diseases, weeds, nematodes and parasitic weeds using PGPR, little is known about the potential of some Bacillus subtilis, B. amyloliquefaciens and Burkholderia phytofirmans strains in sorghum growth promotion and resistance against Striga infection. The main objective of the study was to assess the effect of B. subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans PsJN on growth promotion of sorghum crop and suppression of Striga development, thus providing a basic understanding on the sorghum-PGPR-Striga interaction. This study opens with an elaborate review of the state-of-the-art knowledge on the tripartite interactions between Striga, sorghum and different species of PGPR. Prior to this, bipartite relationship between sorghum and Striga, PGPR-sorghum and PGPR-Striga are reviewed with a focus on understanding Striga impact on sorghum, sorghum defence responses to infection, plant growth and disease suppression benefits by PGPR on sorghum, and the effect of PGPR on Striga development. Knowledge gaps in both bipartite and tripartite relationships are described, and future research recommendations given. A key recommendation from the review is to conduct experiments under controlled environmental conditions using Bacillus subtilis, B. amyloliquefaciens and Burkhoderia phytofirmans strains in order to understand their relationship with sorghum and Striga at bipartite and tripartite levels. Petri dish bioassays and root chamber experiments under controlled conditions were conducted at the Institute of Plant Production and Agroecology in the Tropics and Subtropics, University of Hohenheim between 2012 and 2014. B. subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans strain PsJN inocula and their corresponding cell culture supernatants were evaluated for their growth promotion potential on sorghum and suppressiveness on Striga development. Sorghum root exudates and synthetic stimulant GR24 were used to induce Striga seed germination. Bacillus subtilis Bsn5 supernatant, which showed the greatest inhibitory activity on Striga germination and radicle elongation, was separated by ethyl acetate into lipophilic and hydrophilic phases. The purpose of this extraction was to try and identify the polarity of the inhibitor. Protein composition by mass spectrometry (MS) was also done on the supernatant with a view of establishing the presence of peptides because peptides have been associated with Orobancheceae germination and radicle inhibition in previous studies. In addition, determination of plant growth hormones in bacteria supernatants was also conducted using Radio-Immuno-Assay (RIA) in order to relate PGPR hormone production and sorghum growth enhancement. Burkholderia phytofirmans PsJN significantly (<0.05) induced a higher vigor index (VI) on sorghum seedlings (>18,000) compared to other PGPR and control treatments. The lowest VI (7626) was recorded in seeds inoculated with Bacillus amyloliquefaciens FZB42. Complete Striga germination inhibition (0% germination) occurred in seeds exposed to all PGPR inocula suspended while the highest germination (>60%) occurred in control treatments (10% Luria Bertani (LB) + GR24 and sterile distilled water (SDW) + GR24). The effect of bacterial supernatants on the germination percentage and radicle length of Striga seeds was also significantly (<0.05) different among treatments. The least germination (7.4 %) was observed in Bacillus subtilis Bsn5 + GR24 while the highest (66 %) was observed in SDW + GR24 control. Bacillus subtilis Bsn5 supernatant produced the lowest mean radicle lengths (0.1 mm) while the highest radicle lengths were observed in SDW + GR24 (2.2 mm). Therefore, Bacillus subtilis Bsn5 supernatant was selected for further investigation of compounds causing inhibition of Striga germination and preventing radicle elongation. The supernatant was separated into hydrophilic and hydrophobic fractions using ethyl acetate. Each fraction was then prepared in 1%, 25%, 50%, 75% and 100% concentrations before being evaluated for their inhibitory activity in Striga germination and radicle elongation. The highest germination percentage (63%) and radical length (2.9 mm) was observed in SDW + GR24 control treatment. The ethyl acetate (lipophilic) fraction at both 100% and 1% concentration + GR24 produced a germination percentage of >40% which was similar to 10% LB + GR24 and ethyl acetate + GR24 controls. There was complete inhibition of Striga seed germination after exposure to either Bacillus subtilis Bsn5 supernatant + GR24 or 100% hydrophilic fraction of the supernatant + GR24. However, at 25% and 1% concentration + GR24, Striga germination percentage increased to 34% and 49%, respectively. Light microscopy examination of Striga radicles exposed to Bacillus subtilis Bsn5 supernatant + GR24 revealed that stunting of the radicles was due to reduction in cell sizes at the radicle elongation zone. Extended agar gel assays (EAGA) experiments showed a similar trend of results with B. subtilis Bsn5 showing the highest inhibitory activity on Striga germination and radicle elongation compared to other PGPR and control treatments. Results from root chamber experiments demonstrated significant (p<0.05) differences in biomass production between Striga-free and Striga-infected sorghum. Total biomass yield in uninoculated Striga-free plants was 40% higher than uninoculated Striga-infected sorghum plants. Bacillus amyloliquefaciens FZB42, B. subtilis GBO3 and Burkholderia phytofirmans PsJN inoculated Striga-free sorghum showed a 75%; 142% and 158% increase in biomass yield, respectively, compared to uninoculated Striga-free sorghum. There were no significant differences in biomass yield observed between inoculated and uninoculated Striga-infected plants. All PGPR supernatants and 10% LB media showed production of phytohormones cytokinin, IAA, GAs and ABA. Cytokinin content in PGPR supernatants was significantly (>0.05) higher than blank 10% LB control media. There was a significant negative correlation (r= -0.96) between IAA and cytokinins. However, there was no significant positive correlation between any phytohormone and sorghum plant height, SPAD values, biomass production, Striga germination, attachment and tubercle death. Finally, this study shows that Bacillus subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans PsJN might accelerate sorghum growth and suppress key stages of Striga development under laboratory conditions. Greenhouse and field experiments are recommended to better understand these interactions under natural conditions where other biotic and abiotic factors come into play. These findings could contribute to a better understanding of sorghum and beneficial bacteria interactions and provide novel information of the long-term effects of a PGPR on sorghum development, opening new avenues for Striga control and sustainable, ecofriendly sorghum production.

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