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United States Department of Agriculture

Agricultural Research Service



2010 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. Annual total biomass production averaged 5600 kg ha-1 for corn, 5900 kg ha-1 for wheat, and 3500 kg ha-1 for millet. On more productive soils, total biomass averaged 8500 kg ha-1. We are investigating the quantities of crop biomass needed to protect against erosion and maintain soil carbon. Using observed values to set-up the RUSLE model, average annual water erosion rates ranged from 0.036 - 0.24 t ac-1 yr-1. Similarly, the WEQ model predicted long-term average annual wind erosion rates ranging from 2.3 to 3.6 t ac-1 yr-1, but wind erosion rates increase rapidly under scenarios with biomass removal. We investigated whether or not more intensive cropping systems, relative to wheat-fallow (WF), would be able to maintain soil organic C (SOC) and total N (0-20 cm depth) despite 7 years of drought conditions. Even during drought increased cropping intensity increased SOC and total N, relative to WF, in most of the site and slope positions, indicating that reducing fallow frequency maintains or builds SOC even in drought conditions. Water is also a critical factor for crop production within the context of irrigated cropping systems in Colorado. Demand for water by a rapidly growing municipal and industrial sector is resulting in less water for irrigation. Drought, climate change, and declining groundwater supplies add further stress to the system. This project has identified cropping practices that reduce consumptive water use by 20-50% while maintaining a similar level on-farm income, even without potential income from the saved water. In 2009 we calibrated and validated the CERES-Maize crop growth model for full and limited irrigation conditions and tested the model's ability to differentiate irrigation treatments in terms of ET, crop growth, and yield. The model agreed with observed trends in seasonal ET, corn growth, and yield for full and limited irrigation scenarios. Phenological timing, growth measurements, and yields were in general agreement, although measures of late-season leaf area index in limited irrigation were underestimated, indicating model overestimation of water stress. Simulated cumulative ET trended similar to observed values, although the model showed some tendency to underpredict under full irrigation and overpredict under limited irrigation. Limited irrigation observations showed a significant increase in water use efficiency over full irrigation in two of the three years; however, the model was unable to replicate these results because of underestimation of ET differences between treatments. The CERES-Maize model could benefit from a more robust water stress algorithm that can accurately reproduce plant responses such as those observed in this study. The ADODR monitored progress on this agreement via meetings, conference calls, and site visits.

4. Accomplishments

Last Modified: 2/23/2016
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