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

Abstract

In semiarid climates, efficient precipitation capture and storage arenecessary for successful small grain production.This is especially truein Mediterranean climates dependent on winter precipitation occurringbefore the most active growth and grain development stages of winterwheat (WW, Triticum aestivum L.).The effects of residue cover andtillage 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 threetreatments in annually cropped WW, (i.e., no fallow year), consisting ofno-till (NT), crop residue incorporated with tillage (TI), and cropresidue removed before tillage and then returned to the soil surfaceafter tillage (RR).Field data showed that ground cover from crop residueresulted in more soil water from December 24 through May 20 in thedriest crop year, 2005, of the 3-yr experiment, but no differences inthe two relatively wet crop years 2004 and 2006.The mean soil water in a105-cm profile when treatment differences occurred were as follows; NT =187 mm, RR = 168 mm, and TI = 155 mm.The differences were relativelysmall, 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 couldbe expected to diminish.This research indicates that tillage practicesin the Pacific Northwest have small effect where the land surface isessentially level, but ground cover can play an important role duringexceptionally dry years on precipitation capture and storage.