Water Productivity of Corn and Dry Bean Rotation on Very Fine Sandy Loam Soil in Western Nebraska

Subsurface drip irrigation (SDI) was used to irrigate corn and dry beans in a crop rotation study for four years from 2005 to 2008 to evaluate the accumulative effect of irrigation amount on yield and irrigation water use efficiency (IWUE). This study was conducted on a very fine sandy loam soil using a short season corn hybrid typical for the area. Four irrigation treatments based on providing a fraction of the estimated crop evapotranspiration (ETc) were evaluated. The treatments were designed to replace a certain percentage of ETc and were denoted as I(125), I(100), I(75), and I(50) where the subscript indicates the percentage of ET replacement. The ETc was accumulated, subtracting rain and irrigation amounts, to estimate soil water depletion. Irrigations were made at the various percentages when estimated depletion exceeded the I(100) irrigation amount. The average corn yield response to applied irrigation water was 10.5 kg ha-1 mm-1 (excluding the I(125) treatment). Corn yield was generally statistically different between the I(125) and I(100) treatments and each of the I(75) and I(50) treatments in dry years. Average dry bean yield response to irrigation was 1.5 kg ha-1 mm-1. Dry bean yield was not statistically different. IWUE was calculated by subtracting a representative dryland yield from the measured yield and then dividing by the amount of irrigation water applied. Average IWUE for corn ranged from 17.8 kg ha-1 mm-1 for I125 to 31.1 kg ha-1 mm-1 for I(50) and was not statistically different among all treatments overall due to a year interaction. Corn I(WUE) values were generally statistically different between I(50) and I(125) in most years. Values for corn I(WUE) were similar for I(100) and I(75) treatments. Average I(WUE) for dry beans ranged from 4.55 kg ha-1 mm-1 for I(125) to 9.15 kg ha-1 mm-1 for I(50). Bean IWUE values for the I(50) irrigation treatment were generally greater than the others, especially in dry years. Maximum corn yield occurred with 300 mm of irrigation water in a wet year and approximately 375 mm in dry years. For this study, dry bean yield was highly variable, partly due to treatments being over-watered when based on ETc estimates developed for sprinkler irrigation. Bean yield showed little increase for irrigation amounts greater than 300 mm. Further research is needed examining smaller levels of irrigation, including dryland treatments, as well as different timing treatments based on actual soil water and crop stage of growth.