FALLOW WATER STORAGE IN TILLED VS UNTILLED SOILS IN THE PACIFIC-NORTHWEST

Information concerning soil water storage with no-tillage fallow in th e semiarid winter wheat (Triticum aestivum L.) production areas of the Pacific Northwest is limited. Soil water storage in a long-term tilla ge experiment comparing no-tillage, stubble mulch tillage, and bare so il (moldboard plow) tillage was measured during two 14-mo fallow perio ds in an 11.4-in. annual precipitation area in north-central Oregon. T he greatest precipitation storage efficiency during both years was ach ieved with stubble mulch tillage, followed by the bare soil and no-til lage systems. Residue cover in the no-tillage treatment retarded evapo ration during periods of frequent precipitation and low potential evap oration during the spring, but water loss from no-tillage fallow occur red at the fastest rate during the dry summer due to uninterrupted cap illary 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 zon e drying from fallow, and (ii) stubble mulch tillage, in addition to c ontrolling wind erosion, was slightly more efficient than bare soil ti llage in storing water during fallow.