Soil water dynamics in continuous winter wheat grown in the semiarid Pacific Northwest, U.S.A.

Authors: Williams, John; Wuest, Stewart

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2013
Publication Date: 3/1/2014
Publication URL: http://handle.nal.usda.gov/10113/5927850
Citation: Williams, J.D., Wuest, S.B. 2014. Soil water dynamics in continuous winter wheat grown in the semiarid Pacific Northwest, U.S.A.. Soil Science Society of America Journal. 78(2):571-578.

Interpretive Summary: Wheat production in semi-arid regions depends on how efficiently the limited rainfall is captured and used. Rainfall is not useful if it runs off or evaporates before plants can use it. In this experiment, we examined the role played by tillage practices and surface residue in maintaining water in the soil profile. Water was not lost to runoff at this level site. We examined three treatments used to grow annual winter wheat: no-till (NT), crop residue incorporated with tillage (I), and crop residue removed before tillage and then returned to the soil surface after tillage (RR). In two out of three years of the experiment, there were no differences in soil water, the amount of water available for plant growth. The third year was exceptionally dry, 75% of normal for this region. In this year the treatments with substantial ground cover provided by residue from the previous year’s crop captured more water early in the year. By the end of the rainy season, however, these differences no longer existed. 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.

Technical Abstract: In semi-arid climates, efficient precipitation capture and storage are necessary for successful small grain crop 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 (Triticum aestivum L.). The effects of ground cover and tillage on soil water under annual winter wheat were investigated at Pendleton, OR, on a Walla Walla silt loam, hardpan substratum (coarse-silty, mixed, mesic, superactive Typic Haploxerolls). Three treatments in annual winter wheat consisting of no-till (NT), crop residue incorporated with tillage (I), and crop residue removed before tillage and then returned to the soil surface after tillage (RR). Field data showed that ground cover from wheat residue resulted in more soil water from 24 Dec through 20 May in the driest of the three year experiment, but no differences in the two relatively wet years. The mean soil water in a 105 cm profile when treatment differences occurred were as follows; NT = 186.9±11.1 mm, RR = 167.7±6.6 mm, and I=155.3±4.2 mm. The differences were relatively small, however, with NT 31.7 mm more than the I and 19.2 mm more than RR, and RR 12.5 mm more than the invert treatment. 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.