Dryland Agroecosystem Management for the Central Great Plains

Gary A. Peterson

Co-authors: D.G. Westfall, L.A. Sherrod, and T.M. Shaver

Dryland agriculture in the Central Great Plains historically has consisted of winter wheat-fallow systems with extensive tillage during fallow. This system is highly inefficient in terms of precipitation use efficiency, encourages winter annual weeds, depletes soil organic carbon, accelerates soil erosion, and is economically unstable under current market and policy conditions.

Our overall objective is to identify management systems that improve precipitation use efficiency and net return to the producer. To be sustainable, the systems we identify must also provide erosion control and stabilize the soil organic matter situation.

We established 3 experimental sites in eastern Colorado on farmer-owned land in fall 1985. All sites lie in the 16" to 17" precipitation zone, but vary in potential evaporation from 63"at Sterling (northernmost site), 68" at Stratton, and 78" at Walsh, CO (southernmost site). At each site we are testing cropping systems over a soil catena that has three distinct soil types. Cropping systems tested have been: Wheat-fallow (WF), Wheat-corn-fallow (WCF), Wheat-corn-millet-fallow (WCMF), Opportunity cropping (basically continuous cropping), and native grass. Each phase of a rotation is present every year in the experimental design. All systems are essentially managed with no-till techniques. All yield and residue measurements and soil analyses are done by soil position within each plot. Nutrients are applied based on soil tests for each soil within each cropping system.

Yield and Economic Return: Increasing cropping intensity from WF (2-year) to WCF (3-year) and from WF to WCMF (4-year) has increased annualized grain yield by 75 and 100%, respectively. The change from the 2- to the 3-year system increased net return to the producer by 25 to 40% depending on how the fallow was managed.

Residue cover: Residue cover provides protection against raindrop impact and slows runoff, which increases water infiltration. It also protects the soil against the erosive forces of wind and water. Average residue amounts just prior to wheat planting in WF, WCF, and WCMF have been 1900, 3400, and 3200 lbs/A, respectively. These soils are well protected from erosion even under WF.

Physical changes: Surface soil properties (surface 1") are critical to water capture in dryland agroecosystems. Soils must be able to quickly absorb intense but short duration precipitation events. The key reason is because rapid infiltration discourages evaporative water loss, which is the key water loss mechanism in our summer rainfall area. Increased cropping intensity decreased bulk density and increased total and effective porosity by increasing macro-aggregation. It did not, however, improve sorptivity, which is an index of saturated flow in the surface 1" of soil.

Carbon sequestration: Organic carbon levels after12 years of no-till cropping were increased in direct relationship to the intensification of cropping. Wheat fallow carbon levels did not change significantly over the 12 years, while all other treatments increased in carbon content in the order of WF < WCF < WCMF < Opportunity < Grass. Carbon sequestration rates varied from 45 lbs/A/y with WF to 220 lbs/A/y in the Opportunity cropping system.

Increasing cropping intensity increased annualized grain yields and net income, improved surface soil physical conditions, enhanced carbon sequestration, and provided greater protection against erosion. This has all been possible because of no-till technology, which leaves residue on the surface, enhances precipitation use efficiency and decreases oxidation of soil organic carbon.

Farmers in the Central Great Plains are adopting intensified cropping at an increasing rate. In Colorado alone, dryland corn acreage has risen from an average of 23,700 acres for the 1971-1988 period to 240,000 acres in 1998. Colorado sunflower acreage has increased from 63,000 in 1991 (first year of official sunflower records) to145,000 in 1998. These increases show a shift from wheat-fallow to more intensive cropping systems; meaning that fewer acres are in fallow.

Our project is a joint effort of the Colorado State University Experiment Station and the USDA-ARS. Additional funding from the Western SARE program has been received for satellite studies related to improving diversification in our systems

Gary A. Peterson,
Soil and Crop Sciences Department
Colorado State University
Fort Collins, CO 80523
Tel: (970) 491-6804
gpeterso@lamar.colostate.edu

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