Soil Water Dynamics of Conventional and No-Till Wheat in the Southern Great Plains

Continuous winter wheat (Triticum aestivum L.) represents ~75% of the total grain cropland acreage in Oklahoma. Wheat is mainly sown using conventional tillage (CT), which is linked with low precipitation storage efficiency (PSE), and contributes to water and wind erosion. The objectives of this study were to compare PSE of fallow periods, and water content dynamics of the soil profile during the growing season of winter wheat monoculture under both CT and no-till (NT) systems. Soil moisture was measured weekly from April to November, and every 20 d during the winter period using a neutron probe moisture meter in field experiments at two locations from 2009 to 2011. Significant differences at p < 0.05 level in plant available water (PAW) between CT and NT were observed late in the growing season for one location and year, with CT having PAW values averaging 68 mm greater than NT. Average values of fallow PSE were low, ranging from −10 to 45%. No significant differences at p < 0.05 level were found in fallow PSE and wheat yield with either tillage system. The fallow PSE was 11% in three out of four site-years, which means that often about 90% of summer rainfall is lost. We conclude that soil water dynamics of CT and NT have similar trends during the wheat growing season and that summer fallow PSE in wheat monoculture is inefficient regardless of the tillage system employed.