| The objective of this dissertation was to investigate the role of soil fauna in decomposition and nutrient cycling processes in conventional and no-tillage agroecosystems. Results are described in three chapters. The first chapter describes the trophic structure of the soil nematode community. The second chapter examines the effect of resource quality on the decomposer community, and decomposition and nitrogen mineralization rates in no-tillage agroecosystems. The third chapter evaluates the role of earthworms and enchytraeids in organic matter decomposition and the nitrogen cycle.; The effect of tillage on the soil nematode community trophic structure and the role of nematodes in the regulation of decomposition rates in agroecosystems are described. Tillage affected nematode trophic structure and total abundance. Monthly mean densities of bacterivorous, fungivorous, and total nematodes were greater in conventional than in no-tillage. In the summer, however, fungivorous and plant parasitic nematodes were more abundant in no-tillage.; Decomposition, net nitrogen mineralization rates, microbial and faunal densities on residues of three weed species were quantified at two no-tillage sites. Cassia and Amaranthus, with higher initial nitrogen concentrations and lower C:N ratios, had higher rates of decomposition and net nitrogen mineralization, and greater densities of bacteria, fungi, and nematodes than Sorghum. Densities of fungi were higher on the floodplain than on the upland site and were inversely correlated with fungivore nematode and prostigmatid mite densities at both sites. Despite these differences, decomposition and nitrogen mineralization rates were similar at the two sites for the three species. I estimated that 35% of the weed biomass nitrogen (38 kg N/ha) was mineralized during the 5 month study.; Earthworm and enchytraeid densities and biomass were greater in no-tillage. In Experiment 1 (January to October), earthworms and enchytraeids processed 10 and 17% of the organic matter in conventional and no-tillage, respectively. In Experiment 2 (July to April), earthworms and enchytraeids processed 27 and 10% in conventional and no-tillage, respectively. Earthworms and enchytraeids had a greater impact on fine organic matter in no-tillage. Secondary production of earthworms was 47.34 g AFDW/m{dollar}sp2{dollar}/yr, mean annual standing stock was 14.35 g AFDW/m{dollar}sp2{dollar}, and the annual P:B was 3.30 in no-tillage. Total nitrogen flux through earthworms was 92 kg/ha/yr in no-tillage. |
