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United States Department of Agriculture

Agricultural Research Service

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2007 Annual Report

1a. Objectives (from AD-416)
OBJECTIVES 1. Develop guidelines, protocols and management strategies for irrigated crop production with limited water supplies. a. Determine crop water production functions and weed, and herbicide response to irrigation amount for a four crop rotation under two tillage practices in the Great Plains. b. Develop remote sensing tools and site-specific strategies to efficiently manage water and nitrogen applications for irrigated cropping systems. 2. Develop tools and strategies for site-specific weed management. 3. Develop tools to assess the impacts of cropping systems and irrigation practices on furrow irrigation-induced erosion.

1b. Approach (from AD-416)
We will use small plot field trials to develop water production functions, weed management strategies, and remotely sensed water deficit measurements of four crops (corn, sunflower, wheat and dry beans) under two tillage systems (conventional tillage and minimum tillage). The effects of tillage and limited irrigation on crop yields, weed population dynamics, and herbicide efficacy will be measured. Deficit irrigations will be scheduled to optimize production using past studies of critical growth stages and crop simulation models. Active and passive sensors on ground-based platforms will measure crop response to water and nitrogen stress. The research will be done in collaboration with an agriculture economist and crop modelers to provide basic information for both short and long-term decisions on the best way to maximize economic return with limited irrigation water. Field measurements and computer simulation studies will be used to determine the utility of site specific weed management in growers' fields. We will contribute to an ARS effort to develop a model for NRCS to assess the impacts of cropping systems and irrigation practices on furrow irrigation-induced erosion.

3. Progress Report
Milestone 1: The primary effort to date has been to develop a field site with the necessary infrastructure for a large, multi-year plot study. After investigating multiple sites, a 40 ac site with a good water supply and sandy loam soil, was selected. Preliminary soil maps have been completed and the plot plan has been finalized. The irrigation delivery system has been designed and bid specifications written for the variable rate pumping system. Material lists for the underground delivery system have been completed in preparation for installation in the fall of 2007. Milestone 2: Weed population data under different levels of irrigation were collected in two cooperative experiments. The behavior of atrazine under different levels of irrigation was determined in a cooperative experiment. The movement and dissipation of atrazine depended on the cropping pattern and irrigation system. Atrazine dissipated rapidly in areas that had had 3 years of atrazine use and weed control was very poor whereas in plots where there was no previous application of atrazine the herbicide dissipated more slowly and provided excellent weed control. Milestone 3: A collaborator’s field scale project (Limited irrigation and crop rotation demonstration in the Republican Basin) near Burlington, CO was identified as a potential site. Each quadrant of the center pivot-irrigated field contained a different crop (wheat, corn, soybean, or sunflower) with three irrigation strategies applied (full, intermediate, and allocation). Stationary infrared thermometers (IRTs) along with air temperature and relative humidity probes were installed in the fully irrigated areas of each crop to measure crop canopy temperature to determine the time the crop was under stress due to environmental conditions. Two IRTs were mounted on the center pivot sprinkler to collect data from all irrigation levels as the sprinkler moved around the field. Another site will be the small plot study area near Greeley, CO used for defining water production functions under limited irrigated conditions. Four crops (wheat, corn, dry bean, and sunflower) will be grown in rotation. Two field-sized plots that will be fully irrigated and used for monitoring crop ET with the Bowen ratio, energy balance method will also be instrumented with IRTs. Only two of the four crops can be evaluated each growing season.

4. Accomplishments
Effect of crop rotation on atrazine: Preemergent herbicides are critical for successfully growing corn under limited tillage to prevent early season weed competition with the crop. In a study comparing the behavior of soil applied atrazine to small plots that were under different crop rotations, we found that atrazine dissipated very rapidly in plots that were in the third year of corn. Atrazine had been applied to these plots for three years and pre-emergent weed control was very poor three weeks after application. In a plot that was in a sunflower-wheat-corn rotation, atrazine dissipated more slowly and provided good weed control until the corn canopied. These results indicate that continual application of atrazine selects for soil microbes that can rapidly metabolize the herbicide and affects its effectiveness. NP201: Problem area 6, Problem 6.

4. Accomplishments

5. Significant Activities that Support Special Target Populations

Review Publications
Sojka, R.E., Bjorneberg, D.L., Trout, T.J., Strelkoff, T., Nearing, M.A. 2007. The importance and challenge of modeling irrigation-induced erosion. Journal of Soil and Water Conservation. 62(3):153-162.

Trout, T.J., Kincaid, D.C. 2007. On farm system design and operation and land management. In: Lascano, R.J. and R.E. Sojka (eds), Irrigation of Agricultural Crops, Am. Soc. of Agronomy Monograph #30, 2nd Ed. American Society of Agronomy, Madison, WI, pp 133-180.

Buchleiter, G.W. 2007. Irrigation system automation. Agronomy Society of America, Crop Science Society of America, Soil Science Society of America Meeting.In: Lascano, R.J. and R.E. Sojka (eds). Irrigation of Agricultural Crops. Am. Soc. of Agronomy Monograph #30, 2nd Ed. Am. Soc. Agronomy, Madison, WI. 181-194

Vaughan, P.J., Trout, T.J., Ayars, J.E. 2006. A processing method for weighing lysimeter data and comparison to micrometeorological eto predictions. Agricultural Water Management, Volume 88, Issues 1-3, March 16, 2007, Pages 141-146.

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