Submitted to: Soil Biology and Biochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/9/2000
Publication Date: N/A
Citation: Interpretive Summary: In trying to understand complex biological systems such as the microbial transformations of carbon and nitrogen in soil, it is often helpful to construct a conceptual computer model. One such computer program is NCSOIL, which is part of a larger plant and soil model named NCSWAP. Data from a long-term USDA-ARS field experiment at Rosemount, Minnesota were used to run a sensitivity analysis calibrated on the naturally-occurring tracer carbon from corn residues and soil organic matter. Calibration of the model against a series of kinetic curves gave a 13-year summary quantifying the influence of corn roots, root exudates and soil carbon. The impact of this research will be to provide information to scientists, who ultimately can estimate how managed decomposition of plant residues can help agriculturalists to maintain beneficial levels of organic carbon in the soil.
Technical Abstract: The contribution of below-ground corn photosynthate into soil organic carbon (SOC) was studied by performing a sensitivity analysis of the simulation model NCSWAP calibrated on the naturally occurring tracer C data from a long-term field experiment at the University of Minnesota. Experimental data were obtained from the chisel-plough tillage with no N addition and stover-residue plus grain removed. Simulation of the N and C transformations in the layered soil was performed by the model NCSOIL embedded in NCSWAP. The incorporation of corn-C into SOC was simulated from measured initial soil and corn delta **13C values, or directly by setting 100 percent and 0 percent **13C enrichment in corn and initial soil levels, respectively. The discrepancy between the two methods was minimal. Calibration of the model NCSWAP against 8 kinetic curves - SOC, delta **13 C, and SOC from corn at 0-15 and 15-30 cm depth, above ground dry mass, and droot mass distribution in the soil profile - spanned over 13 years of continuous corn, required 6 units of photosynthate-C translocated as exudates for each unit transferred to roots. One year was required to stabilize the efficiency of corn-C incorporation into SOC when below-ground corn debris were considered an inherent part of the SOC. Following this initial year, the efficiency gradually decreased to about 0.20; or 0.10 with the below-ground corn debris excluded.