Einfluss fermentierter organischer Dünger auf Spurengasemissionen im Ökologischen Pflanzenbau

Agriculture belongs to the major sources of the trace gases nitrous oxide (N2O) and methane (CH4). However, little is known about the contribution of the increasing area of organically managed arable soils in organic farming systems to the greenhouse gas emissions. The objective of our study was the quantification of the in-situ N2O- and CH4- emissions in common organic crop cultivation without livestock. In comparison to this control variant, we focused on the manuring effect of fermented herbal organic matter on the emissions (biogas variant). The straw of the crops and the growth of the intercrops were harvested, fermented in a biogas reactor and applied as fertilizer on the field when the nutrient demand of the crops occurred. The results obtained in 2003/2004 in winter wheat generally revealed a low level of N2O emissions and indicated reduced losses (458 g N ha-1 yr-1) of the soil in the biogas variant compared to the control variant (770 g N ha-1 yr-1). Measurements of the CH4 fluxes showed a slightly decreased CH4 uptake rate in the biogas variant (484 g C ha-1 yr-1) in comparison to the control variant (591 g C ha-1 yr-1)

Relationship between N-cycling communities and ecosystem functioning in a 50-year-old fertilization experiment

International audienceThe relative importance of size and composition of microbial communities in ecosystem functioning is poorly understood. Here, we investigated how community composition and size of selected functional guilds in the nitrogen cycle correlated with agroecosystem functioning, which was defined as microbial process rates, total crop yield and nitrogen content in the crop. Soil was sampled from a 50-year fertilizer trial and the treatments comprised unfertilized bare fallow, unfertilized with crop, and plots with crop fertilized with calcium nitrate, ammonium sulfate, solid cattle manure or sewage sludge. The size of the functional guilds and the total bacterial community were greatly affected by the fertilization regimes, especially by the sewage sludge and ammonium sulfate treatments. The community size results were combined with previously published data on the composition of the corresponding communities, potential ammonia oxidation, denitrification, basal and substrate-induced respiration rates, in addition to crop yield for an integrated analysis. It was found that differences in size, rather than composition, correlated with differences in process rates for the denitrifier and ammonia-oxidizing archaeal and total bacterial communities, whereas neither differences in size nor composition was correlated with differences in process rates for the ammonia-oxidizing bacterial community. In contrast, the composition of nitrate-reducing, denitrifying and total bacterial communities co-varied with primary production and both were strongly linked to soil properties

Abundances and potential activities of nitrogen cycling microbial communities along a chronosequence of a glacier forefield

Glacier forefields are ideal ecosystems to study the development of nutrient cycles as well as single turnover processes during soil development. In this study, we examined the ecology of the microbial nitrogen (N) cycle in bulk soil samples from a chronosequence of the Damma glacier, Switzerland. Major processes of the N cycle were reconstructed on the genetic as well as the potential enzyme activity level at sites of the chronosequence that have been ice-free for 10, 50, 70, 120 and 2000 years. In our study, we focused on N fixation, mineralization (chitinolysis and proteolysis), nitrification and denitrification. Our results suggest that mineralization, mainly the decomposition of deposited organic material, was the main driver for N turnover in initial soils, that is, ice-free for 10 years. Transient soils being ice-free for 50 and 70 years were characterized by a high abundance of N fixing microorganisms. In developed soils, ice-free for 120 and 2000 years, significant rates of nitrification and denitrification were measured. Surprisingly, copy numbers of the respective functional genes encoding the corresponding enzymes were already high in the initial phase of soil development. This clearly indicates that the genetic potential is not the driver for certain functional traits in the initial phase of soil formation but rather a well-balanced expression of the respective genes coding for selected functions