Sorghum and Pearl Millet as Sustainable Alternative Forage Options for Water Limited Environments

Forage maize (Zea mays L.,) is a vital feed crop cultivated for livestock consumption, valued for its high yield potential and nutritional content, but its productivity depends heavily on available water. However, forage sorghum (Sorghum bicolor (L.) Moench) and pearl millet (Pennisetum glaucum (L.) R. Br.) are recognized for their adaptation to drought and heat tolerance, allowing them to achieve high biomass with lower water requirements compared to maize. The goal of this study was to comparatively assess the opportunities and challenges of using sorghum and pearl millet as alternative forages under varying irrigation (full vs limited) and nitrogen (120 vs. 60 lbs. N ac-1) levels to analyze their yield potential, nutritive quality, cyanide potential, nitrates, and silage quality. Field and greenhouse trials revealed significant differences across growth stages, hybrids, treatments, and ensiling days. The soft-dough stage emerged as the ideal harvest stage to obtain maximum yield and nutritional benefits across forage species. Novel prussic acid-free (PF) sorghum hybrids had similar biomass and digestibility compared to maize while maintaining reduced fiber, lignin, and nitrate accumulation compared to conventional sorghum. Irrigation exerted a stronger influence on biomass and fiber content than N application rate. Adequate irrigation enhanced biomass production and reduced digestibility of forage hybrids irrespective of N amount. Non-PF sorghum hybrids produced hydrogen cyanide (HCN) levels far exceeding the critical levels of 500 mg kg-1, while PF sorghum accumulated negligible to low HCN. Forage hybrid had a greater influence on silage quality than management or ensiling length. Peal millet was high in proteins and minerals, maize was energy rich, and PF sorghum maintained a balanced nutrient profile thereby demonstrating its capacity as a promising option under variable water and nitrogen availability. Untargeted metabolomics analysis revealed significant metabolic reprogramming in PF sorghum, with comparable biomass and no yield penalty. The loss of dhurrin led to metabolomic flux being redirected from dhurrin synthesis towards phenylpropanoid and flavonoid pathways, boosting antioxidant production. Prioritizing sorghum and pearl millet forages and adopting innovative approaches presents promising options for ensuring agricultural sustainability in water-limited regions.