Skip to main content
ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Research Project #432376

Research Project: Improving Water Use Efficiency and Water Quality in Irrigated Agricultural Systems

Location: Northwest Irrigation and Soils Research

2018 Annual Report

The research in this project includes a series of studies conducted under two broad objectives of improving water use efficiency and water quality in irrigated crop production. Water use efficiency research focuses on a variety of crops and conditions that occur in the northwestern U.S. Much of the water quality research focuses on the Upper Snake Rock (USR) watershed which is part of the ARS Conservation Effects Assessment Project (CEAP). Objective 1: Improve irrigation water use efficiency by improving irrigation scheduling, infiltration, and soil water holding capacity. Subobjective 1A. Quantify silage corn yield and water use under full and deficit irrigation strategies. Subobjective 1B. Develop and test cultivar specific models for calculating crop water stress index (CWSI) as a tool for irrigation management of wine grape in the arid western U.S. Subobjective 1C. Develop and test a CWSI methodology for deficit irrigation management of sugar beet in an arid environment. Subobjective 1D. Compare soil water balances among tilled and no-tilled, cover crop and no cover crop treatments. Objective 2: Quantify the impacts of management practices on water quality for irrigated crop production at field and watershed scales. Subobjective 2A. Determine annual water balances and nitrate losses in the USR watershed. Subobjective 2B. Determine field-scale furrow irrigation efficiency and sediment and phosphorus losses. Subobjective 2C. Measure leaching under sprinkler and furrow irrigated plots with pan lysimeters. Subobjective 2D. Determine the long-term (5+ years) influence of crosslinked polyacrylamide amendments on soil water drainage, nutrient leaching, and plant nutrient uptake. Subobjective 2E. Develop a simple and inexpensive water-soluble polyacrylamide technology to mitigate sediment and nutrient discharges from horticulture potting soil and nursery beds. Subobjective 2F. Evaluate deep soil sampling as an indicator of nitrate leaching in production fields.

The overall objective of improving irrigation water use efficiency will be addressed through four field studies. A three-year study will be to measure silage corn yield response to four irrigation levels ranging from full irrigation to 25% of full irrigation. Full irrigation is defined as no water stress based on soil water measurements. A second study will develop models for calculating the crop water stress index (CWSI) for specific wine grape cultivars so the CWSI can be used to manage deficit irrigation. The CWSI is calculated from actual canopy temperature and the temperatures of well-watered and severely water stressed crop canopies. The models will be used to predict well-watered and severely stressed canopy temperatures so that vineyards will not need to provide these growing conditions to use the CWSI. A third study will collect canopy temperature data from deficit irrigated sugar beet to apply the CWSI technique to this crop. Previous research has shown that sugar beet yield is not significantly decreased when irrigation is reduced about 20%. Canopy temperature measurement could be a convenient method for managing this deficit irrigation. The fourth study will compare water use between tilled and no-tilled plots with and without a cover crop planted after the main crop is harvested. Additional residue from no-till and cover crop can reduce soil evaporation, however, cover crops will require additional irrigation in an arid region. The second objective will be accomplished through watershed, field, and small plot scale research. Watershed and field scale research will measure the changes in water quality as fields are converted from furrow irrigation to sprinkler irrigation. Irrigation water diverted into the 82,000 ha Upper Snake Rock watershed and water returning to the Snake River in eight return flow streams will be monitored for water quantity and quality to determine water, sediment and nutrient balances for the watershed. Similar monitoring will be done at farm and field scale to provide more detailed measures of irrigation efficiency and sediment and phosphorus losses. A separate study will use pan lysimeters in replicated plots to compare leaching and irrigation efficiency between furrow and sprinkler irrigation. Small-scale field studies will be conducted to evaluate the effectiveness of water-soluble polyacrylamide to reduce nutrient losses from nursery container production and water-absorbent polyacrylamide to improve long-term (5 years) water holding capacity in soil. A final study will assess post-harvest, deep soil sampling techniques as an indicator of nitrate leaching. Some agencies are promoting post-harvest deep soil sampling to evaluate nutrient management. However, sampling at a single point in time does not provide sufficient information to judge if leaching has occurred or will occur. Therefore, soil cores will be collected in the spring and fall for 2.5 years to determine if consistent patterns occur in nitrogen and phosphorus concentration profiles in the soil.

Progress Report
In support of Objective 1, the effects of four irrigation rates (25%-100% of calculated evapotranspiration) on corn silage and grain yields, and soil water content were measured. The response functions for year one were developed. The study will be conducted for two more years, after which the data will be used to develop best management practice tools. Silage and corn grain yield increased as evapotranspiration increased in a quadratic relationship. Real-time monitoring of wine grape canopy temperature for precision irrigation continued on commercial and experimental vineyards. Climatic conditions, wine grape canopy temperatures and soil water content were continuously monitored in three commercial vineyards in southwest Idaho. Climatic and canopy temperature data were used to calculate a daily crop water stress index using cultivar specific models for estimating well-watered canopy temperature. The daily crop water stress index correlated well with soil water content and less well with weekly measurements of mid-day leaf water potential. The crop water stress index and soil water content data were published on a web site for growers to access and use in making irrigation management decisions. Two of the three commercial vineyard managers used the information for making irrigation management decisions. Canopy temperatures of six well-watered wine grape cultivars and climatic conditions were continuously monitored using a wireless network. The data were used to extend the data base of well-watered canopy temperatures for refinement of cultivar-specific models for estimating well-watered canopy temperature based on climatic parameters – solar radiation, air temperature, relative humidity and wind speed. Multiple linear regression and neural network models provide good prediction results when all cultivars are modeled collectively. Overall, cultivar-specific models have less prediction error variance than multi-cultivar models. Multi-cultivar models generally result in prediction bias whereas cultivar-specific models eliminate prediction bias. All predictive models for well-watered canopy temperature result in an uncertainty of +/- 0.1 in calculating crop water stress index despite significantly different prediction error variance between models. Sugar beet canopy temperatures were monitored to develop and evaluate a thermal based crop water stress index. Sugar beet canopy temperature under four irrigation treatments (25, 50, 75 and 100% of estimated evapotranspiration) and climatic conditions (solar radiation, air temperature, relative humidity and wind speed) were continuously monitored in 2017. These data were used to extend the data base of well-watered canopy temperature to refine models for estimating well-watered canopy temperature. Multiple linear regression and neural network models provided good predictions of well-watered sugar beet canopy temperature, but the neural network model provides significantly less prediction error variance than the multiple linear regression model. Both models result in an uncertainty of +/- 0.1 in calculation of the crop water stress index for sugar beet, similar to wine grapes. Soil water extraction profiles were determined for sugar beet irrigated at three deficit irrigation regimes and full irrigation for three growing seasons. Soil water extraction by depth depended on irrigation regime, day of year, and the interaction between irrigation regime and day of year. Sugar beet extracted 15% to 55% of the seasonal water uptake from the top six inches of soil, with deficit irrigation having the highest extraction percentage from this soil depth, possibly because deficit irrigation did not wet the soil deeper than six inches. Cumulative seasonal soil water extraction to a depth of 72 inches represented 90% of soil water extracted regardless of irrigation regime. Soil water was extracted from the 78 to 84 inch soil depth during the growing season for all irrigation regimes, but represented less than 2% of total seasonal soil water extraction from the 84 inch soil profile. Crop yield, soil water content and soil nutrient status were measured for two years on the no-till cover crop study. Residual effects from manure and compost treatments in 1999 are confounding the current study. Thorough soil sampling according to the 1999 experimental design was completed and samples are being analyzed to determine if the current experimental design should be changed. In support of Objective 2, water quality and quantity monitoring in the Upper Snake/Rock watershed continues for the Conservation Effects Assessment Project (CEAP). A survey of about 5% of the watershed using aerial images showed that the amount of the watershed that is sprinkler irrigated has increased from 46% in 2006 to 60% in 2016. Initial analysis for the entire watershed indicates that irrigation water use and the ratio of crop water use to diverted irrigation water has not changed while farms are converting from furrow irrigation to sprinkler irrigation even though irrigation efficiency is likely improving at the field scale. It is difficult for large irrigation projects that deliver surface water to farmers to precisely match irrigation demand, usually resulting in over-supply of irrigation water. Monitoring changed in the PC1 sub-watershed after a new owner converted a farm from furrow irrigation to sprinkler irrigation. The two remaining monitoring sites separately monitor water quality and quantity from the furrow and sprinkler irrigated farms in this sub-watershed. Six additional lysimeter plots were installed in October 2017. The site now has 12 plots with six pan lysimeters in each plot. The entire site is being sprinkler irrigated in 2018 to allow the soil to settle where trenches were dug. Comparing furrow and sprinkler irrigation was unsuccessful in 2017 because furrow irrigation water saturated the soil where trenches were dug for the initial installation. An experiment assessing the long-term influence of crosslinked polyacrylamide (PAM) amendments on soil water retention, nutrient leaching, and plant nutrient uptake was continued. Spring 2017 soil samples were analyzed for soil water retention and chemical analysis of the soil sample is under way. Water retention measurements in spring 2018 soil samples are currently in progress. A plant study determined that a simple water-soluble PAM technology substantially reduces sediment and phosphorus discharges from horticulture potting soil and nursery beds. A second experiment conducted at a commercial nursery was initiated to examine the influence of PAM treatment on two types of potting soils containing flower seedlings. The first experiment was completed and a report is being prepared to present results from the study. An informal cooperative project was completed with the Shoshone Bannock Tribes in Fort Hall, Idaho, to collect six foot deep soil samples in the spring and after harvest. Elevated nitrate concentrations were not detected below the root zone in these sandy soils contrary to results from silt loam soils in Yakima, Washington. Almost 50% of the samples from three to four feet had phosphorus concentrations greater than background sites, which could indicate that leaching is occurring and nitrate has leached below the six foot sampling depth. Between the Spring 2016 and Spring 2017 sampling, soil test phosphorus concentration at five to six foot depth increased more than five parts per million (ppm) in 55% of the samples, four samples increased more than 25 ppm.

1. Sugar beet yield response to irrigation defined. Limited irrigation water supplies can prohibit some fields from being fully irrigated. ARS scientists at Kimberly, Idaho, measured sugar beet yield response to varying irrigation amounts. Estimated recoverable sugar yield increased 0.7 pounds per acre per inch of irrigation plus precipitation and was maximized when actual crop evapotranspiration during the growing season was 29 inches. This research allows sugar beet growers to plan for adequate irrigation supplies and estimate yield losses if adequate irrigation water is not available.

2. Real-time crop water stress index for precise irrigation of wine grapes. Wine grapes are intentionally water stressed to control canopy growth and induce desirable fruit quality, but few techniques are available for continuous real-time plant monitoring. A cellular based information system was used to continuously monitor wine grape canopy temperature, climatic conditions, soil water content, irrigation application, calculate crop water stress index, and display the information on a web site. The information system was installed in three commercial vineyards in southwestern Idaho, and two of the vineyard managers used the real-time information to make irrigation decisions. This technology allows vineyard managers to use real-time plant data to precisely manage irrigation.

3. Long-term linkages between agriculture and groundwater quality. Understanding long-term impacts of agricultural landscapes on shallow groundwater quality is needed to improve soil and water management. In 1999 and 2002-2007, ARS scientists at Kimberly, Idaho, sampled shallow groundwater from drainage tunnels (i.e. man-made springs) that had been monitored in the late-1960s in a 200,000 acre irrigation project. An 8-fold increase in the dairy herd since the late-1960s has increased dairy feed crop production and fertilizer and manure use, while irrigation methods changed from 95% furrow irrigation in 1970 to 60% in 2006. Overall average nitrate-nitrogen concentrations increased 1.4-fold, chloride concentrations decreased 10%, and dissolved phosphorus concentrations decreased 14%. However, dissolved phosphorus concentration increased at some sites near confined animal feeding operations or residential development. This research indicates that further conversion from furrow to sprinkler irrigation alone is unlikely to reduce groundwater nitrate concentrations unless nutrient management is also improved.

4. Greater nitrate leaching from fertilizer than manure with furrow irrigation. A better understanding of nutrient leaching in agriculture is needed to optimize fertilizer use and avoid leaching in furrow irrigated fields. ARS scientists at Kimberly, Idaho, measured drainage water at four foot depth in plots amended with dairy manure, commercial fertilizer, or no-amendment. Even though more total nitrogen was applied with manure than fertilizer, the fertilizer produced 2.6- to 3-fold greater leachate nitrate concentrations and greater total leaching losses. Even the non-amended soils had substantial nitrate-nitrogen leaching (62 pounds/acre per year). In light of the potential negative effects associated with fertilizer, manure and untreated soil, management must minimize percolation water losses during irrigation to limit nitrogen losses.

Review Publications
Ippolito, J.A., Bjorneberg, D.L., Stott, D.E., Karlen, D.L. 2018. Soil quality improvement through conversion to sprinkler irrigation. Soil Science Society of America Journal. 81:1505-1516.
Lentz, R.D., Lehrsch, G.A. 2018. Mineral fertilizer and manure effects on leached inorganic nitrogen, nitrate isotopic composition, phosphorus, and dissolved organic carbon under furrow irrigation. Journal of Environmental Quality. 47:287-296.
Tarkalson, D.D., King, B.A., Bjorneberg, D.L. 2018. Yield production functions of irrigated sugarbeet in an arid climate. Agricultural Water Management. 200:1-9.
King, B.A., Shellie, K. 2018. Wine grape cultivar influence on the performance of models that predict the lower threshold canopy temperature of a water stress index. Computers and Electronics in Agriculture. 145:122-129.
Lentz, R.D., Carter, D.L., Haye, S.V. 2018. Changes in groundwater quality and agriculture in forty years on the Twin Falls irrigation tract in southern Idaho. Journal of Soil and Water Conservation Society. 73(2):107-119.