14C distribution in soil organisms and respiration after the decomposition of crop residue in conventional tillage and no-till agroecosystems at Georgia Piedimont

This study illustrated how crop residue-derived carbon interacts with non-residue carbon (e.g., native soil carbon) in agroecosystems and how carbon is allocated to soil organisms and respiration under different tillage regimes. The carbon dynamics in crop residue, soil microorganisms, nematodes and respiration were monitored using C-14-labeled corn residue. In addition, the carbon budget was estimated for both conventional tillage (CT) and no-till (NT) agricultural ecosystems during the short period after residue application. A laboratory and a field study were conducted separately to assess the above objectives. The results illustrated that the general patterns of carbon allocation were similar in both laboratory and field studies but at a lower magnitude in the field. Most C-14 input to soil was released into air through soil respiration (93-98%) under both CT and NT regimes, with only a small portion bound in microbial (1.8-6.5%) and nematode biomass (0.01-0.12%). However, more C-14 was retained in microbial and nematode biomass under CT than under NT, while the C-14 distributed in soil respiration was similar under both tillage regimes. The C-14 specific activities of soil microorganisms, nematodes and respiration were significantly higher under CT than under NT. The higher C-14 specific activities of soil microorganisms and nematodes, and more C-14 retained in the biomass of soil microoganisms and nematodes under CT, suggested that soil organisms might use C more efficiently under CT than under NT. During the short-term experiments, cumulative soil respiration was significantly higher but residue-derived carbon contributed less to soil respiration under NT than under CT. Consequently, mon non-residue carbon (e.g., native soil carbon) was decomposed and respired by soil organisms under NT than under CT after 40 days of the residue application. It is suggested that residue application might cause a net loss of soil carbon in agroecosystems possibly because of the priming effect of crop residue, particularly under NT regime under the short term. (C) 2000 Elsevier Science B.V. All rights reserved.