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

The dynamics of soil organic carbon (SOC) play an important role in long-te rm ecosystem productivity and the global C cycle. We used extended laborato ry incubation and acid hydrolysis to analytically determine SOC pool sizes and fluxes in US Corn Belt soils derived from both forest and prairie veget ation. Measurement of the natural abundance of C-13 made it possible to fol low 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 tim e (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 4 0-80 y for C-3-derived C depending on soil type and location. No-till manag ement 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 t o 30% at depth. The isotopic composition of SOC mineralized during the earl y stages of incubation reflected accumulations of labile C from the incorpo ration of corn residues. The CO2 released later reflected C-13 characterist ic of the C-s pool. The C-13 Of the CO2 did not equal that of the whole soi l until after 1000 d of incubation. The SOC dynamics determined by acid hyd rolysis, incubation and C-13 content were dependent on soil heritage (prair ie vs. forest), texture, cultivation and parent material, depositional char acteristics. Two independent methods of determining C-3 pool sizes derived from C-3 vegetation gave highly correlated values. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.