Andrew M. McGuire, Extension, Washington State University, Moses Lake, WA and David Granatstein, Washington State University, Wenatchee, WA
The soils in the western U.S., while highly productive under irrigation, are naturally low in organic matter. This gives both a high potential for improvement and causes problems such as wind erosion and associated sand-blasting of seedlings, low infiltration rates, soil crusting, poor drainage, and ponding. It also complicates the concept of ‘soil quality’ which is based on soils with much higher organic matter. Farmers in the irrigated Columbia Basin of Washington state are using organic amendments, cover crops and green manures, and high residue farming (no-till, strip-till) to address these problems. These soil improvement practices vary in their source of added organic matter, tillage intensity, and frequency of application, and so may be expected to have varying effects on the soil. To determine the extent of any effects, we compared the soils of fields managed under these practices to adjacent fields with no soil improvement practices. When the data from all paired fields were analyzed together, soil improvement practices had a highly significant positive effect on soil organic matter, active carbon, and soil protein levels, on available water capacity, and on soil respiration. Neither bulk density nor water infiltration were affected. Results show that, even in intensive crop production, these practices can maintain or improve soils in this region, but that each practice differs from the others in its specific effects.