Best Management Practices for Summer Fallow in the World’s Driest Rainfed Wheat Region

Best Management Practices for Summer Fallow in the World’s Driest Rainfed Wheat Region

William Schillinger, Department Crop and Soil Sciences, Washington State University, Douglas Young, School of Economic Sciences, Washington State University
Wind erosion from excessively tilled soils is a severe problem, especially in south-central Washington. Tillage of fallow land in the world’s driest rainfed wheat production region is considered necessary, but it is also a major safety, environmental, and soil quality concern. This publication outlines the results of a 5-year study to determine the effects of three fallow management systems—traditional tillage, undercutter tillage, and no tillage—and suggests best management practices for farmers in this region.
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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 no-tillage (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.

Introduction

Wheat is produced on 300,000 rainfed acres in the HHH region in south-central Washington (Figure 1). The western portion of the HHH receives as little as 6.0 inches average annual precipitation. An annual average of 8.3 inches of precipitation

Abbreviations

HHH – Horse Heaven Hills

TTF – traditional tillage fallow

UTF – undercutter tillage fallow

NTF – no-tillage fallow

HRW – hard red winter wheat

 

 

Figure 1. Location of the Eastern and Western sites in the HHH. Map courtesy of B.S. Sharratt, USDA-ARS.
falls in the eastern portion. Farmers practice a 2-year tillage-based winter wheat-summer fallow rotation. Given the low precipitation, wheat grain and straw production are generally modest to low (Papendick 2004).

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

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Copyright 2016 Washington State University

Published July, 2016

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