Location:2010 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
This progress report relates to NP Problem area #2.5: Cropping and Tillage Strategies to Best Use Limited Water Supplies and Problem area #6: Water Quality Protection Systems. The second field season of the limited irrigation trials was completed successfully. Good data was collected for the 2009 corn and wheat crops. Data was collected for the dry beans, but yields were below expectations and the sunflower crop, which was abandoned due to herbicide damage. Winter wheat was planted in September 2009 and the remaining three crops were planted in spring 2010. Canopy reflectance, canopy temperature, and images were taken in all plots at least weekly from a boom-mounted platform on a high-clearance tractor to monitor crop growth and development related to the various degrees of plant water stress imposed on the crop by the irrigation scheme. Crop growth stage and plant height were recorded, and intercepted light by the crop canopy measured. Bowen Ratio Energy Balance (BREB) instrumentation was installed in two corn fields (one fully irrigated the other deficit irrigated) and in a fully-irrigated bean field (each greater than 4 ac) to measure crop evapotranspiration (ET). Instrumentation was also installed in each corn field to measure canopy temperature, intercepted light, reflected light, and soil moisture to monitor crop response related to the irrigation scheme. Stationary infrared thermometers (IRTs) were also installed in four of the six irrigation treatments in the corn small plots to detect canopy temperature differences. An analysis of 2008-2009 growing season data showed that the ratio of canopy temperature from water stressed corn to the canopy temperature of fully irrigated corn may be a useful water stress indicator for estimating crop ET. A concept manuscript was prepared, submitted, and recently accepted for publication. To understand the behavior of herbicides under different cropping and irrigation regimes, analysis of the fate of atrazine and metolachlor in corn, flumioxazin and metolachlor in dry beans and sulfentrazone and pendimethalin in sunflower was completed. Good data were obtained that show clear differences in movement among these herbicides in the soil, although most of the herbicides had dissipated to low levels before differential irrigation was applied. We are monitoring the ability of the soil to degrade the atrazine after application. We found that rapid degradation develops within 4 weeks after application of atrazine onto wheat stubble and this ability extends until the following spring. In 2010 these studies were continued. The third year of a study on composition of weed communities was completed and weeds seed production and pattern of emergence was measured under different types of limited irrigation in three crops. Niche modeling was evaluated as a method to predict the occurrence of specific weeds from limited data on where the weed has been observed. Niche models are widely used for predicting the spread of invasive species. A unique optimization algorithm was designed for a spreadsheet-based decision tool to help growers select crops when irrigation water is limited.
1. Modeling forage production under drought conditions. Ranchers need to adjust management when forage production is reduced by drought in order to maximize profit while preventing overgrazing. ARS scientist in Fort Collins, Colorado developed simple models of the relationship between production of mixed grass prairie and precipitation during the spring with data from ND and WY. The accuracy of prediction was improved with information about precipitation in the previous fall for WY. Ranchers experiencing spring drought in some locations will be able to easily predict the reduction of forage production using a spreadsheet that obtains precipitation data available on the internet.
2. Speed of development of enhanced atrazine degradation. Farmers depend on atrazine to provide residual weed control in corn but the continuous use of this herbicide can select for soil microorganisms that can rapidly degrade atrazine. However, it is not known how quickly the soil microorganisms adapt after atrazine application to degrade atrazine. Data from a field trial conducted by ARS and Colorado State University scientists showed that the rate of atrazine degradation increases within 7 days after application and reaches a maximum rate by 40 days after treatment. This ability to degrade atrazine is retained in the soil through the winter and into the following spring. This information is needed by growers who depend on atrazine to provide season long weed control.
3. Corn yield is linearly related to water Consumption. Farmers who irrigate crops but face inadequate water supplies need to know how best to allocate their water. Two years of field studies by ARS scientists at Fort Collins indicate that corn yield decreases linearly as water availability declines. The corn plant is able to efficiently utilize each increment of water to produce an additional increment of yield, up to it’s yield potential, as long as the water is applied when needed by the plant. In the Central Plains, this productivity is about 3 kg of corn grain per cubic meter of water consumed. This simple relationship allows a grower to predict the yield loss and costs of deficit irrigation and to estimate the value of applying additional irrigation water.
Shaner, D.L., Wiles, L., Hansen, N. 2009. Behavior of Atrazine In Limited Irrigation Cropping Systems in Colorado: Prior Use Is Important. Journal of Environmental Quality. 38:1861-1869.