Blowing dust from excessively tilled fallow fields is a major soil loss and air quality concern in the low precipitation (<12 inches annually) wheat production region of the Inland Pacific Northwest (PNW). A 2-year, tillage-based winter wheat-summer fallow (WWSF) rotation is practiced on more than 90% of rainfed cropland in the region. Earlier research proved that the undercutter method for non-soil inversion primary spring tillage is not only environmentally superior but also agronomically and economically equivalent to high-soil disturbance conventional tillage. In this study, we conducted comprehensive surveys of 47 wheat farmers who purchased undercutters through the USDANatural Resources Conservation Service (NRCS). Farmers received 50% cost shares on the condition that they use the undercutter as prescribed by university scientists on at least 160 acres of land for three consecutive years. Participating farmers were interviewed each year from 2008 to 2010 regarding the agronomic and economic performance of the undercutter versus conventional fallow on their farms. The survey revealed equivalent average winter wheat grain yields and profitability for the two systems from 104 paired comparisons. Survey results also showed that 90% of farmer participants were satisfied with the undercutter system. We conclude that the undercutter system offers a costless air quality gain to society and soil conservation benefit for farmers.
This study focuses on the low-precipitation (<12 inches annually) zone of eastcentral Washington and northcentral Oregon that encompasses 3.7 million acres of nonirrigated cropland. Essentially, all this cropland is in a tillagebased WWSF rotation. Excessive tillage during summer fallow causes recurrent wind erosion, which seriously degrades soil, and blowing dust, which poses a hazard for human health. Urban locations within this region frequently fail to meet federal clean air standards for PM10 emissions during windstorms (Sharratt and Lauer 2006). The sandy silt loam soils found throughout the WWSF region have a greater potential to emit PM10 even though these soils are composed of a smaller percentage of PM10 compared to the finertextured silt loam soils found in the intermediate- and highprecipitation zones of the PNW (Feng et al. 2011).
Research conducted in the past two decades indicates that the most realistic method for farmers to mitigate wind erosion and achieve stable and profitable yields in the lowprecipitation zone is to practice conservation tillage in a WWSF rotation. The undercutter system of WWSF farming was developed for this purpose. The undercutter is a primary tillage implement used in the spring to sever capillary pores and channels to halt liquid flow of water to the soil surface as required to retain seedzone water in summer fallow. Undercutter implements are equipped with 32inchwide blades with 28inch spacing between blades on two tiers. Blades have a narrow pitch to allow slicing below the soil surface with minimum soil lifting or disturbance of surface residue (Figures 1 and 2). With this system, a tank cart is pulled in front of the undercutter (Figure 1) to deliver nitrogen, and often sulfur fertilizer, through a manifold and tubing plumbed beneath both wings of individual undercutter blades. The optimal operating depth for the blades is about five inches to provide a relatively thick, dry surface soil mulch to retard evaporation during the summer (Wuest 2010).