Cumulative Deficit Irrigation and Nitrogen Effects on Soil Water Trends, Evapotranspiration, and Dry Matter and Grain Yield of Corn under High Frequency Sprinkler Irrigation

Historically feed corn has been a minor crop in south central Idaho but over the past three decades corn production in southern Idaho has increased fourfold in response to a similar increase in the local dairy industry. Corn seasonal water use and response to water deficits in the region’s climate is lacking. A 3-year field study on corn (Zea mays L.) was conducted in 2017, 2018, and 2019 to evaluate the cumulative effects of continuous water and nitrogen (N) deficits on soil water trends, evapotranspiration, and dry matter and grain yield. Four irrigation rates, fully irrigated (FIT) and three deficit irrigation rates (75% FIT 50% FIT, and 25% FIT) combined with two N supply rates (0 and 246 kg N ha-1) were investigated under lateral-move irrigation. Growing season soil water depletion in 2017 in the 25% FIT and 50% FIT irrigation treatments significantly reduced soil water availability at planting in subsequent years and resulted in reduced yields relative to 2017. Nitrogen treatments had no significant effect on soil water availability, seasonal soil water depletion, or crop evapotranspiration (ETc) for a given irrigation treatment. Crop evapotranspiration was significantly different between irrigation treatments in each study year and decreased as irrigation amount decreased. Dry matter yield was significantly different between irrigation treatments in each study year, but there was no significant difference between the 75% FIT and FIT irrigation treatments for a given N treatment. Differences in dry matter yield decreased between N treatments as irrigation amount decreased. Grain yield was significantly reduced by deficit irrigation in each study year, but there was no significant difference between the 75% FIT and FIT irrigation treatments for a given N treatment in each study year. Grain yield was significantly different between nitrogen treatments for only the FIT irrigation treatment. The lack of significant difference in grain yield between the 75% FIT and FIT irrigation treatments resulted in a curvilinear convex downward water production function regardless of nitrogen treatment. A reduction in applied water resulted in a reduction of grain yield regardless of N availability suggesting that a reduction in irrigation application to less productive areas of a field will cause a yield reduction. The lack of significant difference in crop ETc between N treatments for a given irrigation treatment indicates that crop ETc is unaffected by crop yield potential when soil water contents are similar under high evaporative demand and frequent sprinkler irrigation.