Soil carbon and nitrogen changes following root-plowing of rangeland

Abstract

The effects of root-plowing on soil organic carbon and nitrogen were investigated by comparing paired undisturbed native rangeland with root-plowed sites in the southern Great Plains. Time since root-plowing ranged from 4 to 22 years. We hypothesized that following root-plowing (1) soil carbon would initially drop but recover to the level of untreated range within a 5-10 year period, and (2) the permanent removal of mesquite trees, which enhance ecosystem carbon and nitrogen and provide shade that lowers soil temperature, would result in a slow decline in soil carbon and nitrogen in this ecosystem. There were not significant differences due to treatment for either soil carbon mass (g m-2) (P=0.81) or nitrogen mass (P=0.62). There were significant differences in soil carbon mass (P=0.0014) with respect to elapsed time since plowing. The upper soil layer (0-100mm) had higher carbon levels (P=0.0001) than the deeper soil layer (100-200mm)(1422 +/- 210 g m-2 vs. 1111 +/- 206 g m-2). Differences in soil nitrogen were similar to those of soil carbon. There were significant differences in nitrogen among years-since-root-plowing observations (P=0.003) and the upper soil layer had higher nitrogen levels than the deeper soil layer 138 +/- 18 g m-2 vs. 107 +/- 18 g m-2) (P=0.0001). When the data were analyzed using paired native site values as covariate to account for site differences, the sites that had been root-plowed 4 years previously had higher soil carbon (p