Establishing winter wheat in the dryland Pacific Northwest requires soil water at depths that the seeds are planted in the early fall. Usually, a soil mulch is created and maintained to conserve seed-zone water and to promote the early establishment of winter wheat. Unfortunately, the tillage used to create the soil mulch often results in unacceptable levels of wind erosion. Chemical (no-till) fallow (CF) and reduced-tillage fallow (RT) are two alternatives for reducing wind erosion, but their effectiveness in maintaining sufficient seed-zone water is unknown. Our objectives were to: (i) assess the effects of CF and RT on seed- and root-zone temperature and water; and (ii) test a model (Simultaneous Heat and Water, SHAW) for simulating management effects on soil temperature and water. Weather data, soil temperature, and water content were monitored in CF and RT treatments. The RT treatment was observed to retain more seed-zone water over summer compared to CF. During the wet winter, CF gained more water than RT. Observed soil temperatures were higher in the CF than in RT. SHAW-simulated water contents followed the trend of the field data, though it slightly under-predicted soil water content for CF and over-predicted for RT. We concluded that RT would provide more seed-zone water for winter wheat establishment than CF. In addition, the SHAW model proved adequate in simulating soil water and temperature, and therefore may serve as a useful modeling tool for evaluating tillage and residue management alternatives.
