Browsing by Subject "Agroforst"

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Managing trees on arable land
(2020) Schulz, Vanessa Sarah; Graeff-Hönninger, Simone
The cultivation of several plant species on the same area of land, at the same time, is called Agroforestry (AFS). In the less developed countries and the countries of the tropics and subtropics, AFS are the main form of land management. Reasons can be found in the low degree of mechanization and the low costs of labor. AFS used to be widespread in the industrial nations, too. Over the years, however, these traditional forms have been converted into highly efficient agricultural sites. Agricultural and forest production has been separated spatially. In Germany, this was mainly due to land consolidation, which resulted in large, uniform, and easy-to-farm fields. In recent years, however, this situation has been reconsidered. The positive environmental benefits and the aspect of biodiversity protection of agroforestry systems have been recognized. There are numerous ecological, economic, and social aspects, which make agroforestry attractive again. However, a competitive situation always arises when plants are cultivated together. In addition, there are multiple forms of AFS. Special attention must be paid to the planting of the woody, perennial component, as it remains on the field for several years. Against this background, this thesis deals with the possibilities of establishing the wood component in an AFS as a short rotation strip. Combinations of different tillage and weed management practices on willow growth and yield were tested. Furthermore, the influence of shade, which is listed as one of the three main influencing factors in AFS, is discussed. Agricultural crops behave differently, on shade casts by the woody component on the understory crop, depending on their need for light. To test this, maize was used as a shade-intolerant C4 plant, which reaches its light saturation close to maximum solar irradiance. In contrast, potato was tested as a more shade-tolerant C3 plant. Observations on growth, yield and quality should provide information on their suitability for cultivation under shady conditions in AFS. Various hypotheses were developed and examined for the purpose of testing. In the following, the most central research results will be briefly outlined. When establishing a short rotation coppice with willows, an adequate combination of soil tillage and weed management showed to be important for high yields, whereas the necessary weed management depends on the used soil tillage. Until today, there are no other recommendations for the establishment of a willow short-rotation coppice except ploughing in autumn, harrowing in spring and broad herbicide application. In the current discourse on biodiversity improvement and climate change, forms of reduced tillage (chisel plough + ley crop, no-till) with adapted herbicide-saving weed control (e.g. chemical treatment within the rows and mechanical treatment between the rows, or only mechanical weed control), were tested as alternatives that ensure successful SRC growth and, as a result, high yields while saving pesticides and fossil energy. When grown together, trees will shade the under-story agricultural crops. Some crops can deal better with this light reduction than others. Maize (Zea mays L.), as a plant with a high light saturation point, is already negatively influenced in its growth, the biomass, biogas, and methane yield, as well as the quality determining compounds (dry matter content, crude protein, crude ash) by low amounts of shade. While potatoes (Solanum tuberosum L.), known as shade-tolerant plants, can produce yields and qualities comparable to those of unshaded plants with lower levels of solar irradiance (caused by shading). It could be shown that it is possible to make a valuable contribution to biodiversity with AFS. By using adapted combinations of soil tillage and weed management systems, fossil fuels can be saved through reduced tillage. The use of chemical plant protection in the tree strips can be reduced by the sole application within the SRC strips or avoided altogether by mechanical weed control. In high-valuable timber systems there is usually no weed management necessary. Additionally, the trees strips offer a habitat and food basis for small vertebrates and some arthropods (hymenoptera, coleoptera, lepidoptera and diptera). The permanent planting of the strips reduces greenhouse gases and thus counteracts climate change. Influences of shade on crop yield and quality was only proven for plant-specific shade levels. In such AFS, the influence of shade usually only occurs in later tree ages (and crown thickness). Therefore, AFS are a valuable form of land management to reduce current environmental problems on a national and global scale, while adequate yields can be achieved at the same time.
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.