Corn grain yield as influenced by timing of evapotranspiration deficits

SummaryField experiments were conducted at two sites with differing root zone water holding capacities. Corn grain yield was measured as a function of water management treatments. Stress development in given treatments was generally limited to one of three periods (planting-to-12-leaf, 12-leaf-to-blister-kernel, and blister-kernel-to-physiologic-maturity) during the growing season. Stress levels were defined as low (L), moderate (M) or severe (S) and were based on degree of soil water depletion and an allowable level of leaf xylem pressure depression in midafternoon.Yield vs seasonal ET exhibited linear relationships. Slope of an estimated upper bound function was 0.28 T/ha-cm of water use. Maximum seasonal grain yields were consistently produced with an L-L-L stress sequence allowing about 30–40% depletion of the root zone available water capacity (to 122 cm depth) between irrigations. A trickle irrigated treatment that maintained near zero soil water potential averaged about 4% more yield than the 30–40% depletion criteria, but this difference was not significant at P=0.05.Results, when normalized as relative yield (Y/Ym) vs relative seasonal evapotranspiration (ET/ETm), indicated an upper bound slope of 1.50% yield loss per 1% decline in seasonal ET from the ETm level. When stress was concentrated in the 12 leaf to blister kernel period, the yield reduction slope was 2.60%.Average observed Y/Ym ratios were 0.95 for M-L-L, 0.92 for S-L-L, 0.85 for L-M-L, 0.62 for L-S-L, 0.62 for L-S-L, 0.90 for L-L-M, and 0.69 L-L-S stress sequences.If water stress is limited to one growth period per season an upper bound yield attainment is likely if irrigations relieve stress before available root zone storage capacity is 90–95% depleted in the planting to 12 leaf period, 80–90% depleted in 12 leaf to blister kernel period or when a programmed depletion to 100% available water exhaustion near physiological maturity is achieved in the later grain fill period.Yield reduction of less than 5 % from potential levels appears likely in the climatic setting of this study when root zone available water depletions are limited to 60–70% in the early vegetative period (assumes near field capacity moisture at planting), 30–40% in the 12 leaf to blister kernel period, and 50–60% in the later grain fill period.