The Sanborn Field Experiment: Implications for Long‐Term Soil Organic Carbon Levels

Abstract

With the potential for generating biofuels from crop residues, many scientists and policymakers are seeking data on what would be the long‐term influence of biomass removal on soil organic matter levels. This paper shares the experience of 100 yr of various cropping systems management applications to soil organic carbon (SOC) levels on historic Sanborn Field. Established in 1888, Sanborn Field has employed monocultures and crop rotations to assess the influence of various treatments on crop yield, changes in soil properties, and long‐term sustainability. Soil samples to nearly 1 m from 1915, 1938, 1962, and 1988 for selected cropping management practices were analyzed for SOC. In the initial design of the plot plan, residues from Sanborn Field were removed from plots to simulate the use of these materials in an animal production system. In 1950 the management program was changed to return residues to each specific plot and for increased utilization of N fertilizers. Little increase in SOC was observed in samples from 1962, 12 yr after the return of residues. In many systems, surface SOC decreased from 1915 to 1962 with an increase for the 1988 samples. After initiation of residue return, manure only treatments nearly returned to 1915 SOC contents in the surface soil. This increase was a result of the nutrients from the manure in concert with the residues. SOC distribution over the time period for rotations did not follow the patterns of monocultures. It appears that an equilibrium level of SOC for some cropping systems takes about 30 to 40 yr to develop. Initial active carbon (AC) content assessment as a proxy for soil quality shows greater AC with manure and higher input management systems. The AC had a wide seasonal flux within a growing season as a function of temperature and moisture fluxes on microbial activity.