Fallow water storage in tilled vs. Untilled soils in the Pacific Northwest

Abstract

Information concerning soil water storage with no-tillage fallow in the semiarid winter wheat (Triticum aestivum L.) production areas of the Pacific Northwest is limited. Soil water storage in a long-term tillage experiment comparing no-tillage, stubble mulch tillage, and bare soil (moldboard plow) tillage was measured during two 14-mo fallow periods in an 11.4-in. annual precipitation area in north-central Oregon. The greatest precipitation storage efficiency during both years was achieved with stubble mulch tillage, followed by the bare soil and no-tillage systems. Residue cover in the no-tillage treatment retarded evaporation during periods of frequent precipitation and low potential evaporation during the spring, but water loss from no-tillage fallow occurred at the fastest rate during the dry summer due to uninterrupted capillary flow. Seed zone water content of no-tillage at time of planting in the fall was less than the other treatments. In this study: (i) a tillage operation prior to the period of high potential evaporation in the summer to disrupt pore continuity was required to impede seed zone drying from fallow, and (ii) stubble mulch tillage, in addition to controlling wind erosion, was slightly more efficient than bare soil tillage in storing water during fallow.