ROTARY SUBSOILING EFFECTIVENESS ON RUNOFF AND EROSION IN DRYLAND WHEAT, WASHINGTON

Authors: Williams, John; Wuest, Stewart; SCHILLINGER, WILLLIAM - WASHINGTON STATE UNIV; Gollany, Hero; McCool, Donald

Submitted to: American Water Resources Association Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/2/2003
Publication Date: 11/3/2003
Citation: Williams, J.D., Wuest, S.B., Schillinger, W.F., Gollany, H.T., Mccool, D.K. 2003. Rotary subsoiling effectiveness on runoff and erosion in dryland wheat, Washington. IN: American Water Resources Association 2003 Conference Proceedings, American Water Resources Association, San Diego, CA, Nov. 3, 2003. (Published on CD-ROM, no page number assignment).

Interpretive Summary:

Technical Abstract: The winter wheat-summer fallow production system using conventional inversion tillage methods is used throughout much of the interior dryland cropping area of Oregon and Washington where average annual rainfall is 150 - 350 mm. Inversion tillage and subsequent tillage to control weeds and evaporation in preparation for fall seeding after dry summers leaves the soil surface bare and prone to winter erosion, especially during rain on frozen soil. One possible remedy to this problem is subsoiling, the process of creating pits with long shanks on a roller or pulling a long shank through the soil to open a 600mm deep channel to the subsoil. Some producers consider subsoiling a practical solution to limit or eliminate overland flow and soil erosion under these climatic conditions, and have implemented the practice for years. Investigations into the efficacy of the rotary subsoiler began in the mid 1990's, looking at soil-water changes, rill development on hillslopes, and the impact on crop production. Efforts to evaluate effect of subsoiling on overland flow or erosion were hindered due to less than average number of erosive climatic events from 1998 through 2003. Rainfall simulation was our solution to this problem. We identified a location suitable for rainfall simulation research, in a Bagdad silt loam soil located on property farmed by Jim Els, near Harrington WA. Winter wheat was seeded in September 2002 and plots established in a randomized block design on a continuous hillslope, south aspect, 15% to 25% slope. Two blocks, each containing four plots (two plots per treatment), provided a sample size of eight (n = 8). Treated plots were subsoiled in early November following the first fall rain. We used a simulator designed specifically for the Pacific Northwest, using rain water collected earlier in the winter. Simulation was at a rate of 36 mm/hr onto frozen soil in February 2003, and continued until two hours of overland flow were recorded from each plot. Timed samples were collected in one liter bottles, which were weighed, dried, and reweighed to determine rates of overland flow and erosion. There were no differences between treatments for time to ponding or time to runoff. Total overland flow from plots treated with the rotary subsoiler was significantly less than from untreated plots. Soil loss was similar to the overland flow relationship. For overland flow, the difference between treatments became more apparent as the simulation progressed. Pit effectiveness for erosion control, however, was most important during the first hour after overland flow began. Based on local records, we applied the expected average precipitation for February to each plot. One might speculate that through the course of a normal winter, the pits will fill with soil and become less effective for soil erosion control. Without sustained rainfall, filling-in would be slow, and the pits should continue to be effective through much the winter erosion season. The greatest effectiveness would occur in abnormal winters with early-season frozen soil conditions ending with snowmelt and/or rainfall.