Interactive effects of nitrogen rates and deficit irrigation on yield, forage quality, and water productivity of silage sorghum under subsurface drip irrigation.

This study was conducted to determine the effects of irrigation levels and nitrogen applications on the yield and quality of sorghum (Sorghum bicolor L.) during the years 2021 and 2022 in Isparta, located in the Mediterranean region of Türkiye. The Greengo variety was used in the study. Under a subsurface drip irrigation system, six irrigation treatments representing 0 (rainfed), 25, 50, 75, 100, and 125% of reference evapotranspiration (ET0) replenishment and five nitrogen rates (0, 80, 160, 240, and 320 kg N ha-1) were applied. The experiment was conducted as a split-plot arrangement in a randomized complete block design with three replications. Measurements included Ky (yield response factor), crop water consumption, WUE (water use efficiency), IWUE (irrigation water use efficiency), plant height, number of leaves, stalk thickness, leaf/stalk ratio, green forage yield, dry matter yield, crude protein content (CP), crude protein yield, NDF (neutral detergent fiber), ADF (acid detergent fiber), crude ash, phosphorus, potassium, calcium, magnesium, leaf greenness (SPAD), and stomatal conductance. Irrigation levels and nitrogen rates significantly affected all measured traits. The Ky ranged from 0.805 to 1.479, crop water consumption from 394.2 to 795.6 mm, plant height from 185.0 to 327.7 cm, green forage yield from 31.91 to 114.76 t ha-1, crude protein content from 5.94% to 7.23%, NDF from 46.37% to 57.77%, and ADF from 25.83% to 35.93%. Overall, full irrigation (I100) combined with 240 kg N ha⁻¹ provided the best overall balance between forage yield, forage quality, and irrigation water use efficiency and is therefore recommended as the optimum management strategy for silage sorghum production.