WATER-USE EFFICIENCY OF DOUBLE-CROPPED WHEAT AND SOYBEAN

Many studies have demonstrated that double cropping wheat (Triticum aestivum L.) and soybean [Glycine max (L.) Merr.] allows for greater utilization of natural resources by intensifying cropping practices. A 3-yr study was conducted on a Captina silt loam (fine-silty, mixed, mesic, typic Fragiudult) to determine the water use efficiency (WUE) of winter wheat and to determine the effects of selected management practices on WUE of double-cropped soybeans. The 3-yr mean grain yield of wheat was 3170 kg ha-1 and the mean cumulative evapotranspiration (ET) after 1 April was 32.8 cm. This translated into an average WUE of 96.6 kg ha-1 cm-1 of water. Shortly after wheat harvest, the effect of irrigation, planting date, and stubble management on soybean water use and yield were determined. Irrigation significantly increased soybean grain yield in 2 of 3 yr. The 3-yr yield mean was 2406 and 1704 kg ha-1 for irrigated and non-irrigated soybean, respectively. When irrigation significantly increased grain yield, irrigated soybean had a higher WUE than non-irrigated soybean. Planting date had a significant effect on soybean yield and WUE in only 1 of 3 yr and only when planting date was confounded with row-spacing. Burning of wheat stubble produced significantly higher soybean yields only when herbicide interference by standing wheat stubble was observed. Stubble management had no effect on soybean ET or WUE. The 3-yr mean WUE for the double cropped wheat and soybean system was 79.3 kg ha-1 cm-1 of water.