Tillage intensity and crop residue effects on nitrogen and carbon cycling in a Vertisol

The objective of this study was to examine the impact of tillage intensity and crop residue on carbon (C) and nitrogen (N) cycling in a Vertisol. Soil samples (0–10‐ and 10–20‐cm depth) were collected from a Houston Black soil (fine, montmorillonitic, thermic Udic Pellusterts) with three different levels of tillage intensity, varying from no tillage to complete residue burial. The experiment was a split plot design with five replications. The main plots were three crop species [corn (Zea mays L.), grain sorghum (Sorghum bicolor [L.] Moench), and soybean (Glycine max [L.] Merr.)] and the subplots were three levels of tillage intensity (chisel tillage, reduced tillage, and no tillage). Total N, organic C, inorganic N, and C:N ratio were measured on soil samples as well as the potential C mineralization, N mineralization, C turnover, and C:N mineralization ratio during a 7‐ and 30‐d incubation. Chisel tillage reduced total N, C mineralization, and C turnover at the 0–10‐cm depth compared to the other conservation tillage systems. Following corn production, soil organic C increased and C mineralization and C turnover were decreased at the 10–20‐cm depth compared to the other crop species. This data indicates that, in the short term, tillage systems may control soil organic C at the soil surface, while changes in plant rooting may control soil organic C storage at deeper soil depths in Texas Vertisols.