Soil Water and Water-Use Efficiency in No-Tillage and Sweep Tillage Winter Wheat Production in Northeastern Oregon

The productivity of rainfed winter wheat (WW, Triticum aestivum L.) depends on the efficient capture and storage of precipitation. In the semi-arid Pacific Northwest (PNW), USA, soil water is managed through a 14-mo fallow period to establish wheat before winter and maximize growth potential the following spring. The effects of soil management on soil water storage were investigated on a Walla Walla silt loam soil (coarse-silty, mixed, superactive, mesic Typic Haploxerolls). The treatments were untilled chemical fallow (CF), versus a one-pass undercutter fallow (UF) in 2-yr WW–fallow rotations. These were compared with an annually cropped no-till WW (ANT). Measured from 2007 through 2014, CF had significantly more soil water than UF. Annually cropped no-till WW had less soil water than CF or UF for the duration of the research. These results were not reflected in precipitation capture efficiency. Annualized crop yield was significantly greater in ANT than in CF or UF, which were not significantly different. This resulted in water-use efficiency (WUE) being 30% greater in ANT than CF or UF. Unlike reports from drier zones of the PNW, it appears that CF and even annual wheat production may be ways to maximize WUE by wheat.