A recently released UC Davis report on nitrates in drinking water  in the Tulare Lake Basin and Salinas Valley has elevated discussion about the impact of agricultural activity and nitrogen fertilizers on the quality of drinking water.
The State Water Resources Control Board commissioned the UC Davis Center for Watershed Sciences to conduct a study on nitrate contamination and issue the resulting report, “Addressing Nitrate in California’s Drinking Water,” as required by state legislation. The report states that 10 percent of the people living in agricultural areas in the Tulare Lake Basin and Salinas Valley are at risk for harmful levels of nitrate contamination in their drinking water.
The study implicates agricultural activity — specifically nitrogen fertilizers and dairies  — as the source of 90 percent of the human-generated nitrate contamination in groundwater in those regions. While much of the nitrates present in groundwater have accumulated over the course of decades, it is a problem that will be addressed by, and likely assessed on, growers today.
The report not only lays out the problem based on a collection of existing data, but also offers a number of solutions that may have direct consequences on users of nitrogen fertilizers. It is further mandated that agriculture must do all it can to improve the efficient use of nitrogen fertilizers and minimize off-site movement where fertilizers are applied.
Nitrogen use efficiency
University of California research has demonstrated nitrogen use efficiency, or the percentage of applied nitrogen that is harvested by the crop, in almonds averaging 75 percent to 85 percent under current growing practices. This is among the most efficient measure of any crop in California, and in all agriculture, for that matter.
California almond growers, most of whom are multi-generational family farmers who live and raise their families in rural areas where almonds are grown, share concerns with all Central Valley residents about protecting groundwater quality. These growers, through the Almond Board of California, have invested more than $1.5 million in scientific research focused on improving nitrogen management.
With guidelines generated by this research, almond growers have adopted environmentally responsible farming practices and technologies that have led to significant strides in nitrogen use efficiency in almonds, particularly over the last 20 years.
Twenty years ago almond growers applied nitrogen through broadcast or banded nitrogen materials in large doses, once or twice a season, followed by flood or sprinkler irrigation. Today nitrogen is managed much more efficiently. Thanks in large part to industry-funded research, advances in irrigation and fertilization practices allow for multiple spoon-fed rates of nitrogen that are suited and timed to tree growth and crop demand during the growing season and applied through micro-irrigation systems.
Strides have been made not only in timing and application method, but also in the amount of N applied. ABC-funded research has demonstrated the primary factor dictating N use is crop potential — the total amount applied should be matched to the crop (hulls, shells and kernels) removed with harvest. Over-fertilizing that exceeds this guideline does not enhance yields.
Adopting and applying these principles, almond growers have increased both yield and nitrogen use efficiency.
Two decades ago, the state average yield was 1,200 to 1,300 pounds per acre on a typical nitrogen application of 200 pounds applied N per acre. That is a nitrogen use efficiency of about 44 percent. In contrast, recent results from research conducted by UC researchers demonstrate a yield of 4,000 pounds with 275 pounds of N per acre. That is a nitrogen use efficiency of 75-85 percent, which was attained using current industry practices. This research also documents minimal losses of N: percolation below the root zone averaged less than 5 percent and volatilization was much less than 1 percent.
Almond growers continue to look for ways to even further enhance their nitrogen use efficiency. Programs for continuous improvement, such as the California Almond Sustainability Program, highlight and encourage nitrogen and irrigation management strategies that optimize yield while minimizing impacts to the environment and natural resources.
More research results coming
Research funded by the Almond Board will continue to give growers the tools they need to make improvements. Better information and guidelines, such as new in-season leaf sampling protocols and improved N budgets and models that will offer growers more meaningful and actionable results are on the horizon.
Nitrogen use will continue to be a high-profile public health issue in the San Joaquin Valley. The Almond Board is dedicated to being part of the ongoing discussion to finding workable solutions to providing safe drinking water.
The State Water Board will hold a public workshop on the issue in Sacramento on May 23. The UC Davis report and input from the workshop will be used to inform the board as it develops recommendations for its report to the legislature later in 2012.
Find more information on the May 23 workshop and the UC report, “Addressing Nitrate in California’s Drinking Water”at AlmondBoard.com/farmpress26 .