Bermudagrass Management in the Southern Piedmont USA. III. Particulate and Biologically Active Soil Carbon

Abstract

Quantifying the effects of forage management on soil C cycling improves our understanding of greenhouse gas emissions, agronomic productivity, and changes in soil quality in pasture ecosystems. We evaluated the effects of N fertilization strategy (inorganic only, crimson clover [Trifolium incarnatum L.] cover crop plus inorganic, and broiler litter) and forage harvest strategy (unharvested, low and high grazing pressure, and hayed; representing a gradient from low to high utilization) on particulate organic C (POC), soil microbial biomass C (SMBC), and potential C mineralization (CMIN) during 4 yr on a previously eroded site dominated by Typic Kanhapludults. Accumulation of POC, SMBC, and CMIN with time was greatest at a depth of 0 to 2 cm and was not different among fertilization strategies. To a depth of 6 cm, POC accumulated at a rate of 65 to 73 g m−2 yr−1 under unharvested or hayed strategies and at a rate of 136 to 144 g m−2 yr−1 under cattle grazing strategies. Accumulation rate of SMBC was also dependent upon forage utilization, averaging 5.1, 9.6, 11.9, and 7.4 g m−2 yr−1 under unharvested, low grazing pressure, high grazing pressure, and hayed strategies, respectively. The portion of total organic C as CMIN during 24 d increased from 16 g kg−1 initially to 44 ± 5 g kg−1 (mean ± standard deviation among 12 treatments) at the end of 4 yr, without significant treatment effects. Particulate and biologically active soil C pools increased under all forage management strategies, although cattle grazing imparted the greatest increase partly because of the return of feces to soil.