Browsing by Subject "Umweltfaktor"

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Biological regulation of subsoil C-cycling
(2019) Preußer, Sebastian; Kandeler, Ellen
Soils are the largest terrestrial reservoir of organic carbon (OC). Substantial proportions of the stored OC are found in stabilized form in deeper soil layers. Beside the quality and quantity of C input from plant biomass, C storage in soil is primarily controlled by the microbial decomposition capacity. Various physical, chemical and biological factors (e.g., substrate availability, temperature, water content, pH, texture) vary within soil profiles and directly or indirectly influence the abundance, composition and activity of microbial communities and thus the microbial C turnover. While soil microbiological research has so far focused mainly on processes in topsoil, the mechanisms of C storage and turnover in subsoil are largely unknown. The objective of the present thesis was therefore to investigate the specific influence of substrate availability and different environmental factors as well as their interactions on microbial communities and their regulatory function in subsoil C-cycling. This objective was addressed in three studies. In the first and second study, one-year field experiments were established in which microbial communities from different soil depths were exposed to altered habitat conditions to identify crucial factors influencing the spatial and temporal development of microbial abundance and substrate utilization within soil profiles. This was achieved by reciprocal translocation of soils between subsoil horizons (first study) and topsoil and subsoil horizons (second study) in combination with addition of 13C-labelled substrates and different sampling dates. In the third study, a flow cascade experiment with soil columns from topsoil and subsoil horizons and soil minerals (goethite) coated with 13C-labelled organic matter (OM) was established. This laboratory experiment investigated the importance of exchange processes of OM with reactive soil minerals for the quality and quantity of dissolved OM and the influence of these soil micro-habitats on microbial abundance and community composition with increasing soil depth. In the first study, the reciprocal translocation of subsoils from different soil depths revealed that due to comparable micro-climatic conditions and soil textures within the subsoil profile, no changes in microbial biomass, community composition and activity occurred. Moreover, increasing microbial substrate utilization in relation to the quantity of added substrate indicated that deep soil layers exhibit high potential for microbial C turnover. However, this potential was constrained by low soil moisture in interplay with the coarse soil texture and the resulting micro-scale fragmentation of the subsoil environment. The bacterial substrate utilization was more affected by this spatial separation between microorganisms and potentially available substrate than that of fungi, which was further confirmed by the translocation experiment with topsoil and subsoil in the second study. While the absolute substrate utilization capacity of bacteria decreased from the more moist topsoil to the drier subsoil, fungi were able to increase their substrate utilization and thus to partially compensate the decrease in C input from other sources. Furthermore, the addition of root litter as a preferential C source of fungal decomposer communities led to a pronounced fungal growth in subsoil. The third study demonstrated the high importance of reactive soil minerals both in topsoil and in subsoil for microbial growth due to extensive exchange processes of OM and the associated high availability of labile C. In particular copiotrophic bacteria such as Betaproteobacteria benefited from the increased C availability under non-limiting water conditions leading to a pronounced increase in bacterial dominance in the microbial communities of these soil micro-habitats. In conclusion, this thesis showed that subsoil exhibits great potential for both bacterial and fungal C turnover, albeit this potential is limited by various factors. This thesis, however, allowed to determine the specific effects of these factors on bacteria and fungi and their function in subsoil C-cycling and thus to identify those factors of critical importance. The micro-climate in subsoil, in particular soil moisture, was the primary factor limiting bacterial growth and activity, whereas fungi were more strongly restricted by substrate limitations.
Einfluss von Anbauverfahren und Umweltfaktoren auf Ertrag, Qualität und agronomische Eigenschaften von Soja (Glycine max L. Merrill)
(2021) Sobko, Olena; Gruber, Sabine
With a crude protein content of approximately 40% and a crude fat content of approximately 20% in the seeds, soybean (Glycine max L. Merril) is one of the worlds most important crops with a wide range of uses. The high-quality soybean protein is an important component of animal feed in dairy and meat production. Soybean oil is often used in human nutrition, and with increasing vegetarian or vegan diets, protein-rich foods made from soybean are in high demand. In practical farming, soybean is a beneficial crop in crop rotations because it can fix atmospheric nitrogen through symbiosis with rhizobia, making the plant self-sufficient in nitrogen supply. Since soybean cultivation has no tradition in Germany, optimization of the cultivation technique is required. The present work is about the elaboration of efficient cultivation techniques for soybean in Germany. In three publications, based on three multi-year as well as multi-location and orthogonal field trials, the effects of sowing density and sowing system on yield, protein, and oil content as well as on agronomic properties of soybean are investigated in several varieties from different maturity groups. In addition, the effects of temperature, precipitation and solar radiation on yield, oil content, and protein content have been investigated to identify potential locations for specific production priorities. In the first publication (published in Agronomy Journal MDPI), the results from trials over two years and two locations in southern Germany with four soybean varieties of different maturity groups (00, 000) and growth types with either drill seeding (row spacing 14 cm) or precision seeding (row spacing 28 cm) are presented. To answer the question of which seeding method is more efficient, the following characteristics have been investigated, namely seed yield and yield structure, protein and oil content, LAI, plant height, height of the first pod set, lodging, and nodule numbers. The sowing system did not significantly affect the tested traits, and there was little difference in yield and qualities (seed yield: 3.6 t ha-1 DM, protein content: 40.9 % DM, oil content: 18.8 % DM for drill seeding; seed yield: 3.8 t ha-1 DM, protein content: 40.1 % DM, oil content: 19.1 % DM for precision seeding). These results are very helpful for soybean producers, because they do not need to invest in new sowing technique but can sow with sowing machines which are already available on the farm. The second publication (published in Plant, Soil and Environment) is about the effects of sowing density of soybean with four varieties of maturity groups 00 and 000. Four sowing densities (30, 50, 70, and 90 seeds m-2) were tested over two years and two locations in southern Germany. The lowest seed yield (3.2 t ha-1 DM was obtained at a sowing density of 30 seeds m-2 and the highest at 90 seeds m-2 (4.4 t ha-1 DM). The 00 varieties (3.6 t ha-1 DM) were higher yielding than the 000 varieties (3.4 t ha-1 DM). Sowing density did not affect seed quality characteristics. Plants were more susceptible to lodging with increasing sowing density. The lowest pod set was 4 cm higher at a sowing density of 90 seeds m-2 (13.4 cm) than at 30 seeds m-2 (9.4 cm). Increasing sowing density could reduce yield losses due to threshing because the height of the first pod set was increased at high sowing densities. Consequently, the optimum soybean seed rate would be between 50 and 70 seeds m-2 for 00 and 000 varieties at the tested locations and similar regions in Germany. In the third publication (published in Agronomy Journal MDPI), the influences of environmental factors on yield, protein and oil content, and protein and oil yield of soybean in Germany have been investigated. In the two-year field trials, 13 soybean varieties from maturity groups 00 and 000 were tested at several locations across Germany (four in 2016 and five in 2017). The 000 varieties were less sensitive to environmental factors compared to the 00 varieties. Regardless of maturity group, high solar radiation and appropriate precipitation tended to increase seed yields (r seed yield / solar radiation = 0.32 and r seed yield / solar radiation = 0.33). High temperatures at maturity reduced the productivity but provided slightly higher protein contents in 000 varieties (r protein content / CHU at maturity = 0.23). The locations that are not at risk for water stress would be suitable for soybean production if protein or oil yield is the primary concern. Overall, this study indicates that a sowing density of 50-70 seeds m-2 in combination with varieties of appropriate maturity groups could promote soybean cultivation in Germany. In dry locations, a lower sowing density is advisable in contrast to locations with more precipitation. Additional costs for the adaptation of technical equipment would not be incurred, because both drill seeding and precision seeding can be applied. By matching the direction of use (protein and/or oil production) of soybean to the climatic conditions of specific regions, soybeans for food and feed can be produced in Germany with sufficient traceability for quality and food safety. Climate warming offers opportunities to extend soybean production in Germany. This thesis provides results from which recommendations can be derived that are immediately applicable in agricultural practice.
Life cycle assessment of biogas used for the provision of thermal household energy in developing countries
(2011) Lansche, Jens; Schock, S.; Müller, Joachim
The utilization of dried dung as fuel for household cooking stoves is very common in rural areas of developing countries. The objective of this study was to compare the environmental impacts for the provision of cooking heat from biogas with the utilization of dung cakes. For this purpose, the method of life cycle assessment was used for assessing the impact categories global warming potential, acidification potential, eutrophication potential and human toxicity potential. The results show that anaerobic digestion at household scale can contribute to the reduction of greenhouse gases (GHG?s) as well as several other emissions in rural areas.
Maize boom in the uplands of Northern Vietnam : economic importance and environmental implications
(2008) Zeller, Manfred; Saint-Macary, Camille; Keil, Alwin
In Vietnam, the demand for meat products has grown dramatically due to rapid economic growth and urbanisation and is expected to further increase in the future. Being the primary source of feed for the country?s livestock and poultry industry, maize has become the second most important crop after rice. While this maize boom has the potential to reduce rural poverty, it promotes the expansion of agricultural cultivation into fragile agro-ecological zones, often leading to deforestation and soil degradation, especially in the uplands. Using empirical evidence from mountainous Yen Chau district in north-western Vietnam, the objective of this paper is to investigate the current economic importance and environmental implications of maize cultivation. Furthermore, particular emphasis is placed on the identification of factors influencing farmers? decision how much area to allocate to maize in order to derive research and policy recommendations. Maize is the dominant crop in Yen Chau, covering most of the uplands and generating the lion?s share of households? cash income. Although farmers are well aware of soil erosion on their maize plots, effective soil conservation measures are rarely practiced. Maize is attractive to farmers from all social strata, notably the poor, and through marketing arrangements with traders its cultivation is also not constrained by poor infrastructural conditions. Access to low-interest credit should be enhanced to mitigate farmers? risk of being caught in a poverty trap when maize revenues plummet due to pests, diseases, price fluctuations, or adverse weather conditions. To address the problem of soil degradation in the maize-dominated uplands, research is needed on soil conservation options that are economically more attractive than those promoted thus far.