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United States Department of Agriculture

Agricultural Research Service



2009 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
We evaluated 22 years of wheat and corn yields from dryland cropping systems studies at Sterling, Stratton, and Walsh. A multivariate analysis used stored soil water at planting, and precipitation amounts and timings to relate to crop production in the wheat-corn-fallow rotation. Wheat grain yields were significantly affected by soil water at planting and fallow period rainfall. Wheat yields were not significantly affected by reproductive period rainfall in most cases. Corn grain yields were affected by soil water at planting and reproductive period precipitation but not by vegetative period rainfall. The analysis reveals how critical reproductive precipitation is for spring planted crops but not for fall planted winter wheat, where fallow precipitation is more important. Understanding how a cropping sequence interacts with the rainfall distribution is vital to optimize precipitation use efficiency. We also used the 22 years of wheat and corn yields from Sterling, Stratton, and Walsh to identify key relationships between soil properties and crop production. Based on the wheat-corn-fallow rotation, soil organic carbon, porosity, effective porosity and average contributing slope length are related to yield, with organic carbon having the strongest relationship. The four soil properties predict site specific yield deviations around the site mean with good confidence (r= 0.92) and can be used in process level models. In addition to the analysis of the 22 year dryland cropping system data set, we continue to conduct extensive field studies of water limited cropping systems. The long term dryland cropping systems study was continued at Sterling, Stratton, and Walsh for the 24th consecutive year. On-going results document that intensified crop rotations improve annualized grain yields for intensified crop rotations by 30% to 60% during drought years and as much as 70% in wet years compared to WF. The TDR system installed to monitor soil moisture dynamics at the Sterling site did not function well, was removed, and is being retrofitted for a different location. Limited irrigation cropping systems at sites in Fort Collins and Iliff were continued. Detailed assessments of grain and biomass production, leaf area index, and soil moisture dynamics were made and are being used to test limited irrigation scenarios in cropping system models. ADODR monitoring activities to evaluate research progress included conference calls, meetings with cooperator's personnel, and site visits.

4. Accomplishments

Last Modified: 06/22/2017
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