Crop Rotation Effect on Soil Carbon and Nitrogen Stocks under Limited Irrigation

Limited irrigation management practices are being used in the Central Great Plains to conserve water by optimizing crop water use efficiency. Limited irrigation may reduce total crop biomass production and amount of crop residue returned to the soil. Crop residue production within four no-till (NT) crop rotations [continuous corn (Zea mays L.) (CC); corn-winter wheat (Triticum aestivum L.) (CW); corn-winter wheat-grain sorghum (Sorghum bicolor L. Moench) (CWS); corn-winter wheat-grain sorghum-soybean [Glycine max (L.) Merr.] (CWSSb)] was measured and changes in soil organic carbon (SOC) and total soil nitrogen (TSN) stocks were monitored for 10 yr. Crop residue yields varied with crop being produced and with rotation, as did residue N and C returned to the soil. The C/N ratio of the residue varied with crop. The SOC and TSN pools increased with time in all rotations. The rate of gain in SOC and TSN mass for each rotation was 717, 477, 335, and 270 kg SOC ha(-1) yr(-1) and 114, 92, 87, and 84 kg TSN ha(-1) yr(-1) for the CC, CW, CWS, and CWSSb rotations, respectively, in the 0 - to 30.5-cm soil depth. The rate of change in SOC and TSN mass was lowest with CWSSb (8.7 Mg residue ha(-1) yr(-1)) and highest with CC (12.0 Mg residue ha(-1) yr(-1)). Approximately 6.8 to 7.6 Mg residue ha(-1) yr(-1) would be needed to maintain SOC stocks under limited irrigation.