Effect of Nitrogen Rate and Timing on Forage Sorghum Production and Quality

Forage sorghum is widely used in the southern Great Plains because of its drought tolerance, high biomass productivity, and suitability for multi-cut hay systems; however, information on nitrogen (N) management for forage production and quality in the region remains limited. This study evaluated the effects of N rate and application timing on forage sorghum biomass production and quality at two Oklahoma locations during 2021 and 2023. Biomass production increased with N fertilization at both locations, but response functions differed between sites, with a quadratic response at one location and a linear response at the other. Split N applications primarily altered seasonal biomass distribution by increasing second-harvest regrowth contribution, although total seasonal biomass increased only at the highest split N rate treatment. Forage quality was affected more strongly by harvest timing than by N rate or application timing, with second-harvest forage exhibiting lower fiber concentrations and greater total digestible nutrients. Nitrate concentrations in the forage increased with N rate but remained well below livestock toxicity thresholds. Overall, these results indicate that forage sorghum N management in multi-cut systems should balance sufficient early season N supply to maximize initial biomass production with continued N availability to sustain regrowth productivity and improve seasonal forage distribution.