4. Diversified Cropping Systems
By D.G. Westfall, G.A. Peterson, and N.C. Hansen
The limiting factor for production of dryland crops in semiarid environments is available soil moisture. The wheat-fallow (WF) production system, managed under stubble-mulch tillage, has been the backbone of dryland agriculture in the west-central Great Plains for decades. Over the years, this system has resulted in relatively stable yields because of the soil moisture stored during the fallow period. However, years of tillage for weed control and seed bed preparation have decreased precipitation storage due to soil organic matter loss, degradation of soil structure, increased potential for soil erosion (particularly by wind), and decreased precipitation infiltration. Only about 25 percent of the precipitation received during the 14-month fallow period is stored in the soil for use by the next wheat crop.
Research in Colorado and surrounding states over the past 20 years has shown that it is possible to diversify the cropping system and reduce the frequency of summer fallow by decreasing or eliminating tillage. We can produce crops three out of four years, or more, because of two factors: 1) decreased tillage stores a greater proportion of the annual precipitation in the soil, and 2) having crops present when precipitation initially occurs increases precipitation use efficiency. Adoption of diversified cropping systems also restores soil quality and increases profitability. However, producers must assess their ability and desire to intensify management and accept the increased risk associated with the adoption of diversified cropping systems. Below we outline factors that affect soil moisture storage, cropping systems diversification, and other issues that affect successful production of diversified cropping systems in our water limited environment.