Soil Water Dynamics in Continuous Winter Wheat in the Semiarid Pacific Northwest, USA

Abstract

In semiarid climates, efficient precipitation capture and storage are necessary for successful small grain production. This is especially true in Mediterranean climates dependent on winter precipitation occurring before the most active growth and grain development stages of winter wheat (WW, Triticum aestivum L.). The effects of residue cover and tillage on soil water under annual WW were investigated at Pendleton, OR, on a Walla Walla silt loam soil, (coarse-silty, mixed, superactive, mesic Typic Haploxerolls). These effects were investigated using three treatments in annually cropped WW, (i.e., no fallow year), consisting of no-till (NT), crop residue incorporated with tillage (TI), and crop residue removed before tillage and then returned to the soil surface after tillage (RR). Field data showed that ground cover from crop residue resulted in more soil water from December 24 through May 20 in the driest crop year, 2005, of the 3-yr experiment, but no differences in the two relatively wet crop years 2004 and 2006. The mean soil water in a 105-cm profile when treatment differences occurred were as follows; NT = 187 mm, RR = 168 mm, and TI = 155 mm. The differences were relatively small, however, with NT 31.7 mm more than TI and 19.2 mm more than RR, and RR 12.5 mm more than TI. During normal years these differences could be expected to diminish. This research indicates that tillage practices in the Pacific Northwest have small effect where the land surface is essentially level, but ground cover can play an important role during exceptionally dry years on precipitation capture and storage.