Effect of tillage and nitrogen fertility on growth, yield, and seed chemical composition of rainfed Brassica carinata

The combination of subsoil compaction and injudicious usage of nitrogenous fertilizers are key factors that may lower crop yields, especially in soils with a shallow hardpan. Therefore, the objective of this study was to determine the effects of tillage and N application on carinata productivity in rainfed conditions. A 3-year field study was conducted at the North Florida Research and Education Center, Quincy, FL, USA. Treatments were four rates of N (0, 45, 90, and 135 kg N ha(-1)) and three tillage methods (disking, chiseling, and no-tillage). Maximum cone index measurements for no-tillage occurred at 15 cm but at 20 cm soil depth for both chisel and disk tillage. A hardpan at 15 cm restricted taproot growth but promoted lateral root growth. Subsoiling and N application improved carinata growth relative to no-tillage. Seed yield response to N application rate depended on the tillage method. The agronomic maximum seed yield occurred at 134, 128, and 125 kg N ha(-1) for chisel, disk, and no-tilled systems. Nitrogen agronomic efficiency was greatest at 45 kg N ha(-1) for the chisel method and 95 kg N ha(-1) for disk and no-tillage. Tillage has a greater potential to increase yields even at relatively low N levels. When tilled, carinata produces 8%-17% greater seed yield at 45 kg N ha(-1) than no-tilled carinata grown with 135 kg N ha(-1). These results indicate that tilling the subsoil and applying 90-135 kg N ha(-1) are required for carinata production in soils with a hardpan.