C-14 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-r esidue carbon (e.g., native soil carbon) in agroecosystems and how carbon i s allocated to soil organisms and respiration under different tillage regim es. The carbon dynamics in crop residue, soil microorganisms, nematodes and respiration were monitored using C-14-labeled corn residue. In addition, t he carbon budget was estimated for both conventional tillage (CT) and no-ti ll (NT) agricultural ecosystems during the short period after residue appli cation. 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 a ir through soil respiration (93-98%) under both CT and NT regimes, with onl y 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 u nder CT than under NT, while the C-14 distributed in soil respiration was s imilar under both tillage regimes. The C-14 specific activities of soil mic roorganisms, nematodes and respiration were significantly higher under CT t han under NT. The higher C-14 specific activities of soil microorganisms an d nematodes, and more C-14 retained in the biomass of soil microoganisms an d nematodes under CT, suggested that soil organisms might use C more effici ently under CT than under NT. During the short-term experiments, cumulative soil respiration was significantly higher but residue-derived carbon contr ibuted less to soil respiration under NT than under CT. Consequently, mon n on-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 applica tion. It is suggested that residue application might cause a net loss of so il carbon in agroecosystems possibly because of the priming effect of crop residue, particularly under NT regime under the short term. (C) 2000 Elsevi er Science B.V. All rights reserved.