In south-central Washington, you’ll find the driest wheat-growing region in the world. With only 6 inches of rain falling per year, farmers use specific practices, including tillage, to conserve water and maximize their yields. But tillage practices also cause problems by kicking up the soil and contributing to huge dust storms throughout the area. So, how can farmers best manage wheat, water and dust in such a dry environment?
New work by Bill Schillinger and Doug Young, professors at Washington State University, provides some answers to that question. Their study, published recently in the Soil Science Society of America Journal, describes the best tillage practices for farmers in the Horse Heaven Hills region located about 200 miles southeast of Seattle. Depending upon their location in this dry region, Schillinger and Young suggest that growers incorporate either no-till or undercutter tillage practices into their rotations to optimize wheat yields and minimize dust.
For many years, farmers in the Horse Heaven Hills have used a 2-year winter wheat, summer fallow rotation. Winter wheat is planted in late summer or fall of one year and harvested in July of the next year. The field then remains fallow (unplanted) for about 13 months until wheat is planted again.
“The purpose of only one crop every other year on a given piece of land is so that farmers can store a portion of the precipitation that occurs during the winter months in the soil,” explains Schillinger. “Then they can plant their winter wheat into that stored water [the next fall].”
By using the winter rain to feed the next wheat crop, farmers can optimize water use. And to avoid losing that stored winter rain, many farmers will till the soil in the spring of the fallow year. Tillage breaks the pores and the channels in the soil through which water can move. Water in the soil, traveling toward the surface to evaporate, will run into this tillage layer. With its pathway blocked, the water is more likely to stay in the soil.
While tillage is beneficial for conserving water, it also causes problems. Soils in the Horse Heaven Hills region are vulnerable to wind erosion. Low rainfall, high winds, limited residue cover, and excessive tillage lead to dust storms. Severe dust storms reduce visibility, close freeways, and cause pile ups.
“There have been many exceedances of the federal air quality standard in Kennewick, which is immediately downwind of the Horse Heaven Hills,” says Schillinger. “There have been 20 exceedances in the last 10 years, all attributed to blowing dust from excessively tilled summer fallow fields.”
In an effort to cut down on wind erosion and still help farmers achieve the highest wheat yields possible, Schillinger and Young compared three tillage practices in two different parts of the Horse Heaven Hills. The tillage treatments were no tillage, traditional tillage, and undercutter conservation tillage. With undercutter tillage, large, smooth blades are swept under the soil surface at a specific depth. There is less mixing of the soil, and the soil surface is minimally disturbed leaving most residue of the previous crop in place. “That significantly reduces blowing dust emissions compared to traditional tillage,” says Schillinger.
The success of the different tillage practices were measured in two different parts of the Horse Heaven Hills. The drier western area sees about 6 inches of rain per year, while the comparably wetter eastern area receives about 8 inches per year.
In the western location, early planting of wheat in the late summer – which is necessary for the best yields – was possible in only one of five study years. In four out of five years, there was so little water in the seed zone of the soil that early planting was not possible. Even traditional tillage or undercutter tillage couldn’t help conserve enough water for early planting. No-till practices resulted in the same yields and net returns since crops had to be planted late (mid-October) regardless of which tillage practice was used.
“The question for those growers is, why even bother doing tillage? Just go to no-till and keep your soil from blowing,” says Schillinger. “You’re so dry out there you’re not going to be planting early anyway. Just accept it.”
In the eastern location where more water was available, tillage practices did make a difference. No-till practices led to less water in the soil, later planting, and lower yields. However, both traditional and undercutter tillage allowed for early planting in all five years of the study. Similar yields and net returns were seen with these two tillage practices.
“In the eastern area, we recommend going to the undercutter tillage fallow method. If you look at the data, you’ll see it is just as good as traditional tillage,” says Schillinger. “You can use this undercutter system and leave more residue, leave more clods on the surface, and really reduce the wind erosion risk.”
Research continues in this dry wheat-growing region as Schillinger and others look for alternative crops and better management tools. Meanwhile, growers can maximize crop yields and minimize wind erosion by reconsidering and adapting new summer fallow management practices.