Soil carbon pools and fluxes in long-term corn belt agroecosystems

The dynamics of soil organic carbon (SOC) play an important role in long-term ecosystem productivity and the global C cycle. We used extended laboratory incubation and acid hydrolysis to analytically determine SOC pool sizes and fluxes in US Corn Belt soils derived from both forest and prairie vegetation. Measurement of the natural abundance of (13)C made it possible to follow the influence of continuous corn on SOC accumulation. The active pools (C(a)) comprised 3 to 8% of the SOC with an average field mean residence time (MRT) of 100 d. The slow pools (C(s)) comprised 50% of SOC in the surface and up to 65% in subsoils. They had field MRTs from 12-28 y for C(4)-C and 40-80 y for C(3)-derived C depending on soil type and location. No-till management increased the MRT of the C(3)-C by 10-15 y above conventional tillage. The resistant pool (C(r)) decreased from an average of 50% at the surface to 30% at depth. The isotopic composition of SOC mineralized during the early stages of incubation reflected accumulations of labile C from the incorporation of corn residues. The CO(2) released later reflected (13)C characteristic of the C(s) pool. The (13)C Of the CO(2) did not equal that of the whole soil until after 1000 d of incubation. The SOC dynamics determined by acid hydrolysis, incubation and (13)C content were dependent on soil heritage (prairie vs. forest), texture, cultivation and parent material, depositional characteristics. Two independent methods of determining C(3) pool sizes derived from C(3) vegetation gave highly correlated values. (C) 2000 Elsevier Science Ltd. All rights reserved.