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5517. Ramig, R.E.. 1989. personal communication. Columbia Basin Agr. Research Center, Pendleton, OR 97801.
About 70% of precipitation is stored in the soil from Sept. 1-Mar. 1 at Pendleton, OR, and from Sept. 1-Apr. 1 at Moro, OR. This would be for the first winter after harvest in a crop-fallow system. The following summer, on fallow ground, from Mar. 1-Nov. 1, all precipitation that occurs is lost plus 20% of the stored moisture, in the <14" rainfall zone on deep soils. For the PNW as a whole, fallow storage efficiency is about 50%. It is about 25% in Nebraska, and 15% in North Dakota. In north central OR, under standing stubble, there is 70% storage in an 8' profile in the first winter. Precipitation averages about 16.5" per year. Over the second winter, about 50% of the moisture is stored under the planted wheat crop. Ramig recommends a double fallow for set-aside ground on Ritzville soils. He points out the need for a winter legume that can grow between 35-50 degrees F, provide cover, and fix nitrogen. In the transition zone, water storage values for those soils as listed in the Soil Survey are higher than the actual field values determined.