Simulating Water Stress in Sorghum-Sudangrass Forage System with Different Nitrogen Sources and Tillage Practices

Conserving soil moisture is an important safeguard for drought resiliency in crop production for the U.S. Southern Great Plains. Conservation tillage and cover crops are tools that can provide cover and protect soils and conserve moisture. We assessed variations in simulated water-stress for sorghum-sudangrass (Sorghum bicolor (L.) Moench x Sorghum sudanense (P.) Stapf.) grown for forage, and examined impacts generated by tillage systems (no-till, NT and conventional, CT) and three spring crops grown for green manures (oat, field pea, grass pea) compared to a control (spring fallow and 60 kg inorganic nitrogen ha−1). We calibrated and validated CERES-Sorghum model before simulating the biomass and agroecosystem functions (crop genetics and management, and soil). Seasonal analysis method was adopted to predict biomass and other water parameters during 2006 to 2015 and available soil water in two contrasting growing seasons (2012, dry; 2015, wet) in central Oklahoma, USA. We modified genotype-specific files and parameters of the ‘Residue’ file to simulate change in available moisture by soil layer. Sorghum-sudangrass produced slightly higher amounts of biomass under NT across years and green-manure crops. Weather variables significantly influenced sorghum-sudangrass during growing seasons. Green manures increased (P < 0.05) biomass production (229 to 328 kg ha−1 yr−1), irrespective of tillage system; 63