Location: Northwest Irrigation and Soils Research2012 Annual Report
1a. Objectives (from AD-416):
Objective 1. Quantify crop water productivity for irrigated crop production practices developed to reduce agriculture’s impact on water resources in arid environments in the northwestern U.S. Objective 2. Develop and validate decision tools, models and design aids to conserve soil and water resources in irrigated agriculture. Objective 3. Quantify the processes controlling sediment and nutrient losses from surface and sprinkler irrigated fields in a watershed, and contribute these data to STEWARDS.
1b. Approach (from AD-416):
The overall project goal is to reduce the environmental footprint of irrigated agriculture in an arid environment while sustaining economic return. Field research will quantify water savings and crop production impacts of rotating a non-irrigated year with irrigated crop production or implementing deficit irrigation management strategies that emphasize sugar beet production. This field research will identify alternatives to permanently reducing irrigated area in water limited situations. Model components will be developed to predict application characteristics of center pivot sprinklers, to simulate dynamic infiltration under center pivot irrigation, and estimate drift losses from center pivot sprinklers. These models will assist sprinkler selection and operation for specific field and soil conditions to reduce runoff, erosion and drift losses. Additionally, watershed monitoring will assess impacts of irrigation and management practices on the quantity and quality of water flowing from an irrigated watershed, emphasizing conversion from furrow irrigation to sprinkler irrigation.
3. Progress Report:
This report documents progress for project 5368-13000-008-00D, which started in December 2011 and continues research from project 5368-13000-007-00D Improved Water Resources Management for Irrigated Agriculture in the Pacific Northwest. Objective 1: Plots were established for the irrigated/non-irrigated crop rotation study with initial soil analysis occurring later this year. The second year of a three-year sugarbeet deficit irrigation study was conducted. The initial year of a sugarbeet tillage study showed that strip-tilled soil was wetter than conventionally tilled soil, even when strip-tilled plots receive less irrigation water. Objective 2: A soil sealing infiltration model has been applied to published rainfall simulator data with good success. Additional infiltration data were collected for local soils using a laboratory rainfall simulator, and the infiltration model was applied to these data sets with good success, too. Wind drift and evaporation losses from center pivot sprinklers were measured using catch cans, bromide tracer and air sampling techniques at wind speeds less than 4 m/sec. This measurement protocol collected greater than 99% of the applied irrigation water for several tests, however, larger volume balance errors occasionally occurred for unknown reasons. Initial results showed that wind drift and evaporation losses were less the 5% of the applied water, considerably less than many published studies that only used catch cans. Objective 3: Water samples have been collected weekly from six main irrigation return flow streams in the Upper Snake-Rock CEAP watershed. Monitoring continued in four sub-watersheds. A fifth site was removed at the landowner’s request. Water flow from thirty-five subsurface drain tunnels/tiles were sampled twice to identify sites for regular sampling. Historical water quality data from 1968-1970 were added to STEWARDS. Objective 3: Coefficients for an empirical furrow irrigation erosion equation were redefined using a multiple regression with field slope, soil erodibilty and furrow runoff. The equation is being validated with field data from southern Idaho and central California.
1. Infiltration model developed for center pivot irrigation. Water application rates under center pivot irrigation commonly exceed soil infiltration rates, especially near the end of the system lateral, leading to off-site runoff and erosion, but more importantly, non-uniform water infiltration within the field. A sealing soil infiltration model developed by ARS researchers at Kimberly, Idaho, was adapted to center pivot sprinkler irrigation. The model was calibrated using published and laboratory rainfall simulation studies with varying droplet kinetic energies and application rates on four soils. Model results showed that a surface seal will form when a center pivot system irrigates bare soil with application rates typical to those used near the end of the system. These results suggest that to maximize infiltration under center pivot irrigation, sprinklers with the largest wetted radius should be selected to minimize application rate regardless of water droplet size.
2. Improved estimates of nitrogen availability in years after a dairy manure application. Farmers need to understand how soil nitrogen changes in years following manure application to maximize nutrient use by crops and minimize nitrogen losses to the environment. ARS researchers at Kimberly, Idaho, measured the amount of nitrogen mineralization in the top 2 feet of soil when manure was applied one to five years earlier. The fraction of the total applied nitrogen that was available for crop use decreased each year at a different rate depending on the manure application rate. These findings will allow growers in semi-arid, irrigated regions to better utilize nitrogen from dairy manure to grow crops.
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