Winter Wheat - Summer Fallow Farming
Using the Undercutter Method

Introduction

Wind erosion is a major problem in the dryland (< 300 mm annual precipitation) winter wheat (Triticum aestvum L.) - summer fallow region of Washington, Oregon, and other areas of the Western United States. Traditional tillage methods are intensive and often bury excessive quantities of residue and pulverize soil clods (Fig. 1). Blowing dust from summer-fallowed fields during wind storms causes many road accidents (Fig. 2) and is the reason why several urban areas fail to meet federal clean air standards.

(click on images for larger photo)

Fig. 1. Excessive tillage buries residue and pulverizes soil clods, leaving soil highly vulnerable to wind erosion.

Fig. 2. Blowing dust from excessively-tilled fields has caused numerous highway accidents, such as this multi-vehicle collision in zero visibility that killed seven people and injured 40 others.

Alternatives to traditional intensive tillage during summer fallow were evaluated over a 13-year period at Lind, Washington. The undercutter method of summer fallow farming employs a wide-blade V-sweep (Fig. 3) for primary spring tillage plus fertilizer injection (Fig. 4).

Fig. 3. An undercutter V-sweep blade with attached 3-bar spring-tooth harrow. As a primary spring tillage implement, the undercutter completely severs capillary pores to halt liquid water movement toward the soil surface as required to retain seed-zone moisture in summer fallow.

Fig. 4. Primary spring tillage plus liquid aqua nitrogen injection with an undercutter V-sweep implement. Note that the majority of residue remains standing and undisturbed.

This is followed by as few as two non-inversion rodweeding operations (Fig. 5). Tillage is reduced from the traditional eight or more operations to as few as three operations using the undercutter method. There have never been any differences between the two tillage systems in precipitation storage efficiency in the soil or in wheat grain yield. The undercutter method always increases surface residue, surface clod mass, and surface roughness, which is estimated to reduce soil loss and airborne particulate emissions by more than 50%, compared to traditional tillage. Even after a 13-month-long fallow period, 30% residue cover is consistently achieved at time of planting winter wheat with the undercutter method (Fig. 6).

Fig. 5. A rodweeder (1-inch-square rotating rod) is operated 4 inches below the soil surface two to three times during late spring and summer to control weeds.

Fig. 6. Thirty percent residue cover at time of planting winter wheat into summer fallow is consistently achieved using the undercutter method.

Due to the recent surge in the cost of diesel fuel and decline in the cost of glyphosate herbicide, the undercutter method of summer fallow farming provides significantly higher net returns to the farmer compared to traditional tillage. Results show a ‘win-win’ situation for both wheat farmers and the environment. 

Conclusions

Long-term research at Washington State University conclusively showed that the undercutter method of winter wheat – summer fallow farming results in equal wheat grain yield and superior profitability compared to traditional tillage. The non-inversion undercutter farming method also provides more residue and a rougher soil surface for protection against wind erosion. With judicious use of herbicides, tillage operations during fallow can be effectively reduced from eight or more with traditional tillage to as few as three with the undercutter method. If the undercutter method of summer fallow were widely practiced, it is reasonable to expect a sharp reduction in wind erosion and suspended dust emissions, with associated benefit to air quality.