Abstract
About 65 to 75 percent of the annual precipitation in the Northwest comes during winter. Warm, moisture-laden storms move in from the Pacific Ocean, commonly when soils are frozen. Precipitation and rapid snowmelt on frozen soils with little or no surface residue can result in significant surface runoff and soil erosion. Loss of topsoil by water erosion seriously affects soil productivity in the Northwest, degrades water quality and causes costly sedimentation problems. Yield potentials are also reduced because of the reduced soil water storage. One of the most severe runoff and erosion problems is from winter wheat seeded on a fine, conventionally tilled seedbed with little or no surface residue. Water and soil losses are especially high after conventional summer fallow. Compacted soil layers can significantly increase runoff and erosion potential. Tillage erosion contributes to topsoil loss on ridge top and upper slopes as well. Conservation tillage systems such as minimum tillage or no-till maintain a higher level of residue on the soil surface. Surface residue, as welol as rough soil surface, slows downslope water movement and reduces runoff by 60 percent or more compared to low-residue conventional tillage. If compacted soil layers are present or runoff on frozen soils is common, deep chiseling can increase water movement into soils and reduce runoff. Surface residue also reduces soil freezing, allowing more water movement into the soil. If runoff does occur, no-till and minimum tillage can still reduce soil erosion by 90 percent or more compared to conventional tillage. A number of options are available for developing minimum tillage and no-till systems. Existing drills can often be modified to improve residue penetration and fertilizer placement. Equipment can be rented or purchased, or custom seeding can be arranged. Minimum tillage and no-till reduce runoff and erosion and also potentially reduce costs while maintaining or increasing production. More producers should begin experimenting to develop efficient conservation tillage systems adapted to individual farming conditions. Contact your County Extension Agent and local Conservation District or Soil Conservation Service office for more information.