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United States Department of Agriculture

Agricultural Research Service



2012 Annual Report

1a. Objectives (from AD-416):
1) Combine expertise of the USDA-ARS, Agricultural Systems Research Unit (ASRU) in process-based models of cropping systems with cutting-edge dry-land and limited-irrigation experimental research of the Colorado State University (CSU), working in collaboration with the leading ARS limited-irrigation Water Management Research in Fort Collins, the ARS dry-land cropping research at Akron, CO, and irrigation research at the CSU Department of Civil and Environmental Engineering, to create a center of excellence in water limited agro-ecosystems research; 2) use 22 years of experimental data on dry-land cropping systems obtained under prior cooperative CSU-ASRU research and on-going CSU limited-water research to advance understanding of biophysical processes in water-limited cropping of the Great Plains and management practices that promote long-term sustainability of agriculture, water, and the environment; 3) synthesize and quantify that understanding with the help of process models of these systems; and 4) develop quantitative, whole-system based, guidance and decision tools for site-specific optimum crop selections and water-related management for the producers.

1b. Approach (from AD-416):
The CSU-ASRU Cooperative field studies of several dry-land crop rotations on three soil types along a sloping catena of soil types, at each of the three eastern Colorado north-south locations, will be continued for another two years. This will complete the cycles of all dry-land crop rotations being evaluated and provide valuable data on the performance of different crop rotations for 24 years, first 12 years with normal to above normal rainfall and the next 12 years with subnormal rainfall. The detailed measurements of rainfall, runoff, and soil water dynamics (to deduce evaporation and plant uptake) on one location, started two years ago, will be continued and enhanced with measurements of water and N balance in limited-irrigation crop rotation research studies in Fort Collins, CO. At the same time, the existing 22 years of experimental data will be analyzed to relate the year to year production of major crops to variable rainfall and soil water availability at different growth stages, soils, topographic locations, and climates, using statistical and process modeling approaches. The data on soil carbon changes under no-till cropping systems available from the above studies will also be quantified with respect to above conditions. Based on the enhanced understanding derived from above analyses, after first two years, new innovative ways to increase precipitation storage efficiency and water use efficiencies by crops, such as by reducing soil evaporation losses, will be explored under controlled conditions. The knowledge and syntheses derived from above studies will be used to derive simpler tools to guide selection of optimal crops (including bio-energy crops) and conservation/management practices for variable water availabilities for sustainable production and environment.

3. Progress Report:
The Colorado long-term dryland agroecosystems project continued in its 26th year of operation. The study, with field locations near Sterling, Stratton, and Walsh, Colorado, maintains comparisons of three original no-till cropping systems, winter wheat – corn – summer fallow (WCF), continuous cropping (OPP), and perennial grass over a soil catena. In 2011, cropping systems added to the study include winter wheat-summer fallow (WF), Winter wheat – forage sorghum – summer fallow (WSfF), and winter wheat – forage sorghum – forage soybean (WSfSoyf). It is hypothesized that inclusion of forage crops will improve climate change adaptation by reducing the frequency of water sensitive crop growth stages, and broaden the diversity of cropping intensity being evaluated. As a part of this project, a review article was published in Field Crops Research that overviews research achievements and adoption of no-till, dryland cropping in the Semi-Arid US Great Plains. The paper identifies no-till as a key management strategy to deal with the high level of temporal and spatial climate variability in the U.S. Great Plains documents and documents adoption of no-till in the Northern, Central, and Southern Great Plains as 25%, 20%, and 5% of cultivated land, respectively. Adoption of no-till is limited in the Southern Great Plains because of the low residue crops often produced and the prevalence of livestock grazing. The adoption of no-till is associated with intensified rotations that reduce fallow, improve precipitation use and soil properties. An emerging concern about adoption of no-till is an altered pest complex for wheat in the Great Plains, including insects, diseases, and weeds. The report further highlights recent research achievements including: 1) informing crop and fallow choice with soil water and climate predictions, 2) alternative and fallow replacement crops, 3) mixed crop livestock systems, and 4) runoff and soil erosion in dryland systems. Water is also a critical factor for crop production within the context of irrigated cropping systems in Colorado. This project has identified cropping practices that reduce consumptive water use by 20-50% while maintaining a similar on-farm income. A major challenge is the need for practical and accurate approaches to verify crop water use and water savings. One approach to verifying crop ET under limited irrigation is to use a crop stress coefficient as a modifier to crop ET estimated using the Penman Monteith equation. We have tested the use of a stress coefficient against limited irrigation corn data from 2008-2010 at the Iliff, Colorado research site. The stress coefficient is calculated based on soil water depletion relative to a crop specific maximum allowable depletion (MAD). We have found reasonable ET estimation using a MAD of 55% for corn. Ongoing work is evaluating other verification approaches including remote sensing of ET, crop water stress index, and using stress coefficients with standard energy balance equations and crop coefficients. Farmer interest in dryland and limited irrigation cropping systems continues to be strong as demonstrated by demand for information and by practice adoption rates. Dryland corn acreage increased from 23,700 in 1986 to an average of 230,000 over the last 5 years, reflecting a 10-fold increase. When considering other crops including sunflower and millet, summer crop acreage has increased by about 500,000 in Colorado since 1986. Assuming that summer crops are grown in a 3 year rotation (wheat summer crop fallow), it means there are about 1,500,000 acres under more intensive cropping systems compared to 75,000 in 1986. The Colorado Water Conservation Board has estimated that as much as 300,000 acres of irrigated land will be converted to dryland or limited irrigation practices to meet growing urban water demand. Both producers and water suppliers have publicly testified that our research is addressing a critical need in the Great Plains. Impact Statement: Intensive dryland cropping systems build soil organic carbon, improve soil quality, and improve both air and surface water quality because they provide high amounts of year around cover. These benefits have been realized for about 1,500,000 acres in CO that have been converted from wheat-fallow to wheat-summer crop-fallow. This conversion increased net return by $22,275,000 per year under normal precipitation conditions. Limited irrigation cropping systems based on conservation tillage practices demonstrated in this project build soil organic carbon, improve soil quality, and improve both air and surface water quality because they provide high amounts of year around soil cover. These benefits have the potential to affect as much as 2,000,000 acres in CO. We have documented limited irrigation cropping systems water conservation as much as 350 mm yr-1 compared to fully irrigated corn while maintaining similar on-farm economic returns. Survey results from this project document that irrigated farmers in the South Platte River Basin have a willingness to adopt limited irrigation cropping systems and that there will be adequate water savings to meet projected urban water demand through water lease arrangements. Invited presentations from our project team have reached over 1,200 people from diverse audiences in Colorado during this reporting period.

4. Accomplishments

Last Modified: 10/18/2017
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