IMPACT OF WATER AND NITROGEN AVAILABILITY ON MAIZE EVAPOTRANSPIRATION AND SOIL WATER TRENDS UNDER HIGH FREQUENCY SPRINKLER IRRIGATION

Abstract

<sc>Abstract.</sc> One potential advantage of variable rate irrigation (VRI) is that less water can be applied to field areas with low productivity, without adversely affecting yield, thereby reducing water use, nutrient leaching, and pumping costs. This inferred potential advantage of VRI has not been fully evaluated experimentally. A three-year field study on maize (Zea mays L.) grain yield was conducted to test the hypothesis that high and low productivity has no effect on crop ET. High and low productivity were established using high and low soil nitrogen (N) supplies. The effect of 0 kg N ha^-1 (low N supply) and 246 kg N ha^-1 (high N supply) application under fully irrigated (FIT) and three limited irrigation rates (75% FIT, 50% FIT, and 25 FIT) on maize grain yield and soil water trends were investigated in 2017, 2018 and 2019 under lateral-move irrigation in south central Idaho. Maize evapotranspiration (ET_c), grain yield and soil water contents were significantly different (p < 0.05) between irrigation treatments and study year. Grain yield decreased nonlinearly as seasonal irrigation amount decreased regardless of N supply. The maize ET_c and soil water contents from the two N rates within each irrigation level were the same. During each year of the study and within each irrigation treatment, there were no significant (p < 0.05) maize ET or soil water content differences between the N treatments. Assuming yields under different N application rates were representative of high and low maize productivity areas of fields, the results show that reducing water application to low productivity areas will reduce grain yield at the same rate as in high productivity areas. Thus, VRI does not provide the opportunity to reduce water use and pumping costs while maintaining yield levels in low production areas