WATER REQUIREMENT OF SUBSURFACE DRIP-IRRIGATED CORN IN NORTHWEST KANSAS

Irrigation development during the last 50 years has led to overdraft i n many areas of the large Ogallala aquifer in the central United State s. Faced with the decline in irrigated acres, irrigators and wafer res ource personnel are examining many new techniques to conserve this val uable resource. A three-year study (1989 to 1991) was conducted on a K eith silt loam soil (Aridic Argiustoll) in northwest Kansas to determi ne the water requirement of corn (Zea mays L.) grown using a subsurfac e drip irrigation (SDI) system. A dryland control and five irrigation treatments, designed to meet from 25 to 125% of calculated evapotransp iration (ET) needs of the crop were examined. Although cumulative evap otranspiration and precipitation were near normal for the three growin g seasons, irrigation requirements were higher than normal due to the timing of precipitation and high evapotranspiration periods. Analysis of the seasonal progression of soil water revealed the well-watered tr eatments (75 to 125% of ET treatments) maintained stable soil water le vels above approximately 55 to 60% of field capacity for the 2.4-m soi l profile; while the deficit-irrigated treatments (no irrigation to 50 % of ET treatments) mined the soil water. Corn yields were highly line arly related to calculated crop water use, producing 0.048 Mg/ha of gr ain for each millimeter of water used above a threshold of 328 mm. Ana lysis of the calculated water balance components indicated that carefu l management of SDI systems can reduce net irrigation needs by nearly 25%, while still maintaining top yields of 12.5 Mg/ha. Most of these w ater savings can be attributable to minimizing nonbeneficial water bal ance components such as soil evaporation and long-term drainage. The S DI system is one technology that can make significant improvements in water use efficiency by better managing the water balance components.