Impact of irrigation and nitrogen fertilizer rate on soil water trends and maize evapotranspiration during the vegetative and reproductive periods

Field research was conducted in 2011 and 2012 at the University of Nebraska-Lincoln South Central Agricultural Laboratory located near Clay Center, NE to evaluate maize actual evapotranspiration (ETa) during the vegetative and reproductive growth periods for 0, 84, 140, 196, and 252 kg ha⁻¹ nitrogen (N) fertilizer treatments under full irrigation (FIT), limited irrigation (75% of FIT), and rainfed settings. Daily ETa values were greatest during the early reproductive period (silking to blister growth stages) with average values of 3.62, 5.18, and 5.91 mm d⁻¹ in 2011 and 4.37, 5.92, and 6.12 mm d⁻¹ in 2012 for rainfed, 75% FIT, and FIT, respectively. Maize ETa during the vegetative period was not significantly impacted by N fertilizer rate in 2011 (P_0.05 = 0.2357) or 2012 (P_0.05 = 0.6341). Whereas, reproductive period ETa for FIT and 75% FIT for the pooled years significantly increased with N fertilizer rate with slopes of 0.20 and 0.17, respectively. The rainfed regression slopes were not statistically different from zero in 2012 (P_0.05 = 0.1467) or pooled years (P_0.05 = 0.0505). The increase in reproductive ETa with N fertilizer and irrigation resulted in a positive grain yield response with slopes of 0.021, 0.048, and 0.104 Mg ha⁻¹ mm⁻¹ for the rainfed, 75% FIT, and FIT settings, respectively.