Best management practices for summer fallow in the world's driest rainfed wheat region

Abstract

The Horse Heaven Hills (HHH) located in south-central Washington contains the world’s driest rainfed wheat production region where farms receive as little as six inches average annual precipitation. Late summer establishment of winter wheat into carryover seed-zone water after a year of fallow is essential to achieve the highest grain yield potential. Tillage of fallow land during the spring is considered necessary to retain adequate seed-zone water during the dry summer months, but blowing dust from excessively tilled fallow is a major safety, environmental, and soil quality concern. The objective of this 5-year study was to compare the effects of three fallow management systems on soil water dynamics, wheat stand establishment, grain yield, and economic returns on two farms in western and eastern portions of the HHH where long-term annual precipitation averages 6.0 and 8.3 inches, respectively. Fallow management treatments were: traditional tillage (TTF), undercutter tillage (UTF), and notillage (NTF). This publication documents that NTF in the western HHH and UTF in the eastern HHH are best management practices for farmers and the environment in a region where wind erosion from excessively tilled soils is a severe problem. Soils in the HHH are highly vulnerable to wind erosion due to the dry environment, high winds, limited straw cover, and intensive tillage during fallow. These soils contain high quantities of PM10-sized particulates (i.e., less than 10 micrograms in diameter) that, when exposed, are readily transmitted hundreds of miles in the air stream by suspension (Sharratt et al. 2007). Major dust storms may occur several times a year (Sharratt and Edgar 2011). Exceedances of the US Federal Air Quality Standard for PM10 occurred 20 times between 2000 and 2010 in the city of Kennewick, WA, which is located immediately downwind of the HHH (Sharratt and Edgar 2011). The highest daily PM10 concentration measured in Kennewick during this time period was nearly ten times the concentration allowed by law. All of these PM10 exceedances were attributed to windblown dust.