Location: Northwest Irrigation and Soils Research2019 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.
In support of Objective 1, research studies are continuing that evaluate techniques to improve irrigation management. The third and final year of research to determine deficit irrigation effects on corn silage and grain yields is being completed in 2019. Irrigation has been applied at four rates for three years to the same plots to determine the cumulative effects of reduced irrigation. Research continued to develop and test cultivar specific models for calculating and using the crop water stress index (CWSI) as an irrigation management tool in wine grape. Climatic conditions, soil water content, and vine canopy temperature were continuously monitored in wine grape cultivar Malbec, irrigated at three rates in an experimental vineyard at Parma, Idaho. Net radiation was also measured, and the data were used to calibrate a physical model for estimating non-transpiring vine canopy temperature. The calibrated model was then used to calculate CWSI for cultivars Malbec and Syrah, based on data collected at the site in 2014, 2015 and 2016. Daily average CWSI was found to have a highly significant quadratic relationship with midday leaf water potential with a correlation coefficient of 0.64 for both cultivars combined. This outcome indicates that daily average CWSI is a good indicator of vine midday leaf water potential, which is the standard method for assessing vine water stress and managing irrigation. Climatic conditions, soil water content, and vine canopy temperature were continuously monitored in four commercial vineyards in southwest Idaho. The data were used to compute a daily average CWSI that was correlated with weekly measured midday leaf water potential. The daily average crop water stress index and soil water content data were published on a web site for vineyard managers to use in making irrigation management decisions. Two of the four commercial vineyards adopted daily CWSI for making daily irrigation management decisions. One vineyard manager wanted to purchase multiple CWSI monitoring systems. Climatic conditions and vine canopy temperature of wine grape cultivar Pinot noir irrigated at four rates were continuously monitored in a commercial vineyard in southwest Oregon to assess regional transferability of wine grape CWSI models developed for Idaho conditions. Vine midday stem water potential was also measured weekly. Daily average CWSI had a highly significant quadratic relationship with stem water potential with a correlation coefficient of 0.66. The results indicate that the methodology developed for estimating wine grape CWSI in Idaho is applicable to southwest Oregon climatic conditions. Researchers continued to develop and test CWSI methodology for deficit irrigation management of sugar beet. Climatic conditions and canopy temperature of sugar beet irrigated at four rates were continuously monitored in 2018. The data were used to enhance the data base of well-watered canopy temperature for refinement of models for estimating well-watered canopy temperature based on climatic parameters. Both multiple linear regression and neural network models provided good prediction of well-watered sugar beet canopy temperature, but the neural network model provided significantly less prediction error variance. A physical model to estimate non-transpiring canopy temperature was calibrated using the collected database. Well-watered and non-transpiring temperatures are needed to calculate CWSI. Climatic conditions and canopy temperature of sugar beet irrigated at three rates were continuously monitored in 2018 near Powell, Wyoming, to assess regional transferability of sugar beet CWSI models developed for Idaho conditions. Using the models developed in Idaho, calculated CWSI was a better indicator of water stress than soil water measurement in deficit irrigated plots. The results indicate that CWSI models developed for sugar beet in Idaho are applicable to Wyoming climatic conditions. Detailed soil sampling in the cover crop study plots documented wide variability in nitrogen concentrations, possibly due to manure legacy effects. Nitrogen variability will likely overshadow effects of cover crops and no-tillage. Winter wheat was planted in Fall 2018 without any fertilizer while future management strategies are being determined. In support of Objective 2, water quality and quantity monitoring in the Upper Snake/Rock watershed continues for the Conservation Effects Assessment Project (CEAP). Additional water samples were collected monthly in 2019 to determine the level of antibiotic resistance genes and related genetic determinants in irrigation return flows during a calendar year. Selected antibiotic resistance genes were targeted for investigation because they include resistance to antibiotics that are considered medically important to humans. All of the genes were detected throughout the year and levels were generally greater during the irrigation season when surface runoff/subsurface drainage rates are higher. The genes were also detected in irrigation water flowing into the watershed which originates in the Snake River, but the gene levels were lower than found in the irrigation return flows. No relationships were found between the water quality characteristics and the abundance of the genes in the return flows. The results from this study suggest that surface irrigation runoff contributes to the increased abundance of antibiotic resistance genes in the environment. Annual and monthly water balances were calculated for 2006 to 2016 for the Twin Falls irrigation project that delivers surface water to 200,000 acres of crop land in the Upper Snake/Rock watershed. Irrigation water diverted from the Snake River was 75 to 89% of the total annual inflow into the watershed, while precipitation was only 10 to 23% of the inflow. Rock Creek, an ephemeral stream, only contributed 0.5 to 2% of the total inflow. Annual evapotranspiration equaled 57 to 67% of watershed inflow and 27 to 34% of the total annual watershed inflow flowed back to the Snake River. A study was completed that determined the temporal character and source of leached nitrate in the Upper Snake/Rock watershed. Stable isotope ratios of nitrate and water were measured in drain tunnel and irrigation waters collected from 2003 to 2007 and leachate from incubated urea- and manure-amended soil in a recent laboratory study. The study determined that: 1) 20 to 23 months are required for water and nutrients to move from the soil surface to the shallow groundwater, 2) nitrate concentrations in shallow groundwater are a function of nitrate leaching loads from local agricultural soils and dilution from regional groundwater contributions, 3) 1.5 times more nitrogen in shallow groundwater was derived from fertilizer and fixed nitrogen than from animal waste, 4) the dominant nitrogen cycling processes in these soils is mineralization of soil organic matter and the nitrification of ammonium derived from applied fertilizer and manure (not denitrification), and 5) future changes in regional groundwater nitrate concentration can be expected as it slowly equilibrates with the effects of post-1960s expanded fertilizer application, possibly increasing shallow groundwater contamination. Pan lysimeters were installed in 12 plots in 2016 and 2017. These plots were sprinkler and furrow irrigated in 2019 to compare leaching that occurs from these two irrigation methods. During the first irrigation, leachate was collected in 11 of the 36 lysimeters in furrow irrigated plots and no leachate was collected from sprinkler irrigated plots. An experiment assessing the long-term influence of crosslinked polyacrylamide and polyacrylate amendments on soil water retention, nutrient leaching, and plant nutrient uptake was completed. Soil water retention and water penetration resistance for spring 2018 soil samples, and soil nutrient concentrations for spring 2017 soil samples were measured. This study is the first designed to examine long-term benefits of crosslinked polymers in an agricultural setting. The knowledge it provides to the industry and farmers is important because it shows that the soil water retention benefits from crosslinked polyacrylamide are far more persistent than previously known, which has crucial ramifications regarding the economic viability of the practice.
1. Converting from surface irrigation to sprinkler irrigation. Water is applied more uniformly with sprinkler irrigation than surface irrigation. Conservation programs support conversion to sprinkler irrigation to improve irrigation efficiency and water quality; these improvements have been well documented for individual fields. ARS researchers at Kimberly, Idaho, calculated water balances in a 200,000-acre irrigation project as part of the Conservation Effects Assessment Project (CEAP). The percentage of sprinkler irrigated land increased from 45% to 60% from 2006 to 2016. Irrigation project efficiency, however, did not increase because the amount of irrigation water diverted into the watershed did not decrease due to the supply-based irrigation diversion policy. To improve watershed-scale irrigation efficiency, water policies need to enable irrigation diversion based on crop irrigation need in addition to applying conservation practices on individual fields.
Holly, M.A., Kleinman, P.J., Bryant, R.B., Bjorneberg, D.L., Rotz, C.A., Baker, J.M., Boggess, M.V., Brauer, D.K., Chintala, R., Feyereisen, G.W., Gamble, J.D., Leytem, A.B., Reed, K., Vadas, P.A., Waldrip, H. 2018. Identifying challenges and opportunities for improved nutrient management through U.S.D.A's Dairy Agroecosystem Working Group. Journal of Dairy Science. 101(7):6632-6641. https://doi.org/10.3168/jds.2017-13819.
Lentz, R.D., Lehrsch, G.A. 2018. Temporal changes in 18O and 15N of nitrate nitrogen and H2O in shallow groundwater: Transit time and nitrate-source implications for an irrigated tract in southern Idaho. Agricultural Water Management. 212:126-135. https://doi.org/10.1016/j.agwat.2018.08.043.
Ippolito, J.A., Bjorneberg, D.L., Blecker, S.W., Massey, M.S. 2019. Mechanisms responsible for soil phosphorus availability differences between sprinkler and furrow irrigation. Journal of Environmental Quality. 48:1-10. https://doi.org/10.2134/jeq2019.01.0016.