Water productivity of forage sorghum in response to winter cover crops in semi-arid irrigated conditions

Forage sorghum (Sorghum bicolor (L.) Moench) is a suitable alternative for corn silage in water-limited environments due to its similar yield potential as corn but with less water input. Cover cropping could further improve forage sorghum yield and water productivity, making it the best alternative forage crop for arid and semi-arid regions. This two-year study evaluated the effect of fallow and cover crops on soil volumetric water content (VWC), soil water extraction, changes in soil water storage (Delta S), seasonal crop evapotranspiration (ETseasonal), cropping system evapotranspiration (ETsystem), seasonal crop water productivity (CWPseasonal), cropping system water productivity (CWPsystem) and forage sorghum yield under a no-till semi-arid irrigated condition. Treatments included three winter cover crop mixtures: grasses + brassicas + legumes (GBL), grasses + brassicas (GB), grasses + legumes (GL), and a no-cover crop control (fallow), arranged in a randomized complete block design with four replications. Cover crops significantly reduced soil VWC at the beginning and up to 30 days after sorghum planting (DAP). However, at 60 DAP, the VWC was mostly similar among all treatments, and at 90 DAP, it was 17-21% higher under the cover crop treatments than fallow. The ETseasonal was 22-26% higher under cover crops than fallow during cover crop growth, but it was 12-13% greater under fallow than the cover crops during forage sorghum growth. Total soil water extraction at sorghum harvest was 8-89% higher under fallow than cover crops treatments. Averaged across years, cover crop biomass yield was 11% greater with the GBL mixture than the GB and GL mixtures. Forage sorghum yield was 23%, 32%, and 18% higher under GBL, GB, and GL cover crop mixtures, respectively, than fallow. Compared to fallow, cover crop mixtures improved sorghum CWP by 38-43%. Results indicated that forage sorghum yield and CWP under semi-arid irrigated systems could be substantially improved with winter cover cropping than leaving the land fallow.