Evapotranspiration and Yield Comparisons among Soil-Water-Balance and Climate-Based Equations for Irrigation Scheduling of Sweet Corn

As water for crop production becomes limited and costs of water increase there is a need for more accurate irrigation scheduling. Irrigation scheduling can be improved with reliable and rapid estimates of crop evapotranspiration (ET). The use of three climatebased equations and the soil-water-balance equation for estimating sweet corn (Zea mays L. ‘Jubilee’) ET for irrigation scheduling were compared in a 2-yr field study on a mixed, mesic Cumulic Ultic Hapoxeroll soil. The three climate-data-based equations used were the Food and Agriculture Organization of the United Nations (FAO) modified Penman and the FAO and Soil Conservation Service (SGS) Blaney-Criddle equations. Five irrigation levels ranging from 0 to 100%, with the 100% level intended to refill the root zone to field capacity, were all proportionately irrigated when approximately 50% of the available water was depleted in the 100% level as measured with a neutron meter. A sixth treatment in this randomized complete block experiment was irrigated with the amount of water equivalent to the crop ET estimated by the FAO modified Penman (M PEN) equation, when the crop ET had accumulated to 50% of the available soil water. The crop ET estimated by the soil-water-balance equation in 1984 was 481 and 447 mm for the 100% level and for plots irrigated according to the M PEN equation, respectively. In 1985 these ET estimates were 506 and 488 mm, respectively. The crop ET in 1984 was 404, 372, and 374 mm as estimated by the M PEN, FAO, and SGS Blaney-Criddle equations, while in 1985 these equations estimated 450,448, and 379 mm, respectively. Yield differences were not significant between plots irrigated according to the M PEN equation and the irrigation levels of 50% or more in both years. Calculations indicated that the lower estimates of ET by the FAO and SCS Blaney-Criddle equations, if used to schedule irrigations, would not be expected to cause yield decreases.