Agronomic Response of Silage Maize to Varying Irrigation Water and Nitrogen Levels Under Subsurface Drip Irrigation: Implications for Yield and Water Use Productivity.

Excessive or poorly timed nitrogen (N) fertilization can increase nitrate leaching and associated environmental risks. This two-year field study evaluated the combined effects of three irrigation regimes and four N rates on the biomass yield, water productivity, and economic performance of silage maize under subsurface drip irrigation (SDI). The irrigation treatments were full irrigation (I1), 50% of I1 (deficit irrigation, I2), and 120% of I1 (excess irrigation, I3); the N treatments were 0 (N0), 140 (N1), 210 (N2), and 280 kg N ha-1 (N3). The experiment was established in a randomized complete block split-plot design with three replications during the 2022 and 2023 growing seasons. Seasonal irrigation ranged from 198 to 471 mm in 2022 and from 214 to 470 mm in 2023. The N1I2 treatment consistently produced the highest green forage yield (109,520 and 112,330 kg ha-1 in 2022 and 2023, respectively) while using approximately half the irrigation water applied to I1. It also produced the highest reported water productivity and irrigation water productivity, with values of 42.4 and 55.3 kg m-3 in 2022 and 44.4 and 52.5 kg m-3 in 2023, respectively. According to the partial-budget analysis, N1I2 generated the highest net profit (USD 31,941.83 ha-1 in 2022 and USD 28,500.08 ha-1 in 2023) and relative profit ratios of 4.17 and 11.48, respectively. Under the soil, climate, and price conditions of this study, applying 140 kg N ha-1 with deficit irrigation at 50% of the full-irrigation amount provided the best balance among biomass production, irrigation water use, and economic return.