2013 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.
The overarching objective of the project is to advance understanding of biophysical processes in water-limited agro-ecosystems and develop management practices that promote long-term sustainability. The project has been conducted based on field research studies in both dryland and limited irrigation agroecosystems where water limitations are the most important management decisions. Research has involved field observations, data analysis, and cropping systems modelling to address key, management related factors to improve crop water productivity.
The dryland components of the study are based on the Colorado long-term dryland agroecosystems project, which has been in continuous operation for 27 years. The study has a unique physical design that incorporates time and comparisons over three locations (Sterling, Stratton, and Walsh) that represent a gradient in the severity of water deficit. The study evaluates the effects of contrasting, no-till based crop rotations over time and space and the influence on soil properties, water use, and crop productivity. 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 a traditional wheat fallow system. The field observations were used to validate a modelling study evaluating the sustainability of harvesting crop residues from drylands as a potential biomass feedstock. The major constraint to sustainable residue harvest was maintenance of SOC. Virtually all of the corn or wheat stover production, an average of 2250 kg ha-1 yr-1, must be left in the field to maintain SOC. The long term data set was used to explore the relationships between crop yield variability and soil profile water at planting and rainfall during various plant growth stages. For wheat yields, the rainfall during the preceding fallow period was highly related to soil water content at planting and was the most important variable for prediction of yield. Predicting corn yield was much different that for wheat and was most dependent on rainfall during reproductive growth. For both wheat and corn or sorghum, the 24-year mean yields were strongly related to key soil properties, especially soil carbon content. 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 and documents adoption of no-till in the Northern, Central, and Southern Great Plains as 25%, 20%, and 5% of cultivated land, respectively. A recent focus has been on the adaptation of cropping systems to climate change.
The limited irrigation component of this project 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. The practices consist of rotations that involve low water use crops, limited irrigation, and partial season irrigation. Field data was used to calibrated, validate, and improve the CERES-Maize crop growth model for full and limited irrigation conditions and the model was used to evaluate a variety of alternative irrigation management strategies. Another major effort has been devoted to testing of practical and accurate approaches to verify crop water use and water savings. Results show reasonable agreement between observed ET and ET calculated with a crop stress coefficient to modify ET calculated with a Penman Monteith equation and crop coefficient. The stress coefficient for corn was determined using a maximum allowable depletion (MAD) of 55%. Another approach evaluated was the Crop Water Stress Index (CWSI), calculated based on remotely sensed canopy temperature. CWSI related to both soil volumetric water content and crop transpiration rate and was reasonably accurate for computing crop water use.
Conversion of about 1,500,000 acres in CO from wheat-fallow to wheat-summer crop-fallow has increased net return by $22,275,000 per year, based on an increased return of $14.85/acre as documented by the most recent economic analysis. Intensive dryland cropping systems build soil organic carbon and improve soil quality. These systems also improve both air and surface water quality because they provide high amounts of year around cover that reduces soil erosion by 80 to 90%. 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.