Can Irrigation Timing Ameliorate High Night Temperature Stress on Corn?.

Corn growers in the Wintergarden region of southwest Texas typically use high-stature varieties that inevitably incur excessive respiratory carbon loss from roots and transpiration water loss under high night temperature conditions. By integrating corn breeding and crop management, we hope to increase yield, harvest index and water use efficiency while using varieties with shorter ear height. We tested this possibility in Uvalde, TX, considering genotype (ear height), environment (high night temperature stress) and management (irrigation timing-induced root-zone cooling) interactions. The experiment was conducted in 2014 and 2015 using 24 plots arranged as a factorial design, with 3 corn hybrids (low-ear, high-ear and a control hybrid BH9029) and 2 irrigation-timing (day-time vs. night-time drip) treatments each replicated 4 times. From March to July, 2014, a total of 175 mm irrigation water was applied in 11 events. Day-time irrigation was given starting 9:00-10:00AM and the night-time irrigation was given starting 5:00-6:00PM. Twelve minirhizotron tubes were installed to a depth 45 cm to measure root growth. Plant height, ear height and leaf chlorophyll levels were measured at silking stage. Upon harvest, kernel nutrients were analyzed using an NIR system. Although 2014 had a relatively cool summer, our data suggest that delivering irrigation at night-time through drip, as compared to day irrigation, can significantly increase root length (p=0.035), plant height (p=0.027) and marginally increase grain yield (p=0.074). However, irrigation timing did not significantly affect leaf chlorophyll level and kernel crude protein, phosphorous, fat and starch concentrations. As the high-ear hybrid was more prone to smut infection in 2014, the effect of ear-height on yield was inconclusive, although high-ear hybrid yielded lower than lower-ear or the control hybrid (p=0.004). In 2015, additional measurement of soil respiration rates will be conducted to quantify the effect of irrigation timing on soil CO2 efflux.