Priming of soil organic carbon decomposition induced by corn compared to soybean crops

Abstract

The rate of soil organic carbon (CS) loss via microbial respiration (decomposition rate k, y1), and the rate of stabilization of vegetation inputs (CV) into CS (humification rate h, y1) are usually considered inde- pendent of CV. However, short-term laboratory studies suggest that the quality and quantity of CV con- trols k, which is often referred to as a priming effect. We investigated how the chemical composition of different residues, (corn and soybean) controls k and h under field conditions in a no-till ecosystem. Using CV-driven shifts in d13C, we estimated changes in carbon (C) stocks, k and h of both the labile particulate organic matter fraction (CPOM) and the stabilized mineral associated organic matter fraction (CMAOM). After two years of high C inputs (corn: 4.4 Mg ha1 y1 aboveground and C:N 1⁄4 78; soybean: 3.5 Mg ha1 y1, C:N 1⁄4 17), we found no changes in CPOM and CMAOM stocks in the top 5-cm of soil or in deeper layers. However, CMAOM in corn had higher k (0.06 y1) and C output fluxes (0.67 Mg ha1 y1) than in soybean (0.03 y1 and 0.32 Mg ha1 y1), but similar rates and fluxes in CPOM in the top 5-cm of soil. In addition, while C inputs to CPOM were also similar for both crops, C inputs from CV to CMAOM were higher in corn (0.51 Mg ha1 y1) than in soybean (0.19 Mg ha1 y1). Overall, corn plots had higher k and C inputs into CMAOM and therefore higher C cycling in this fraction. Our data suggests that the type of crop residue strongly influences C cycling in the topsoil of no-till cropping systems by affecting both the stabilization and the decomposition of soil organic matter.