Earlier this year, scientists at UC Davis released a report entitled “Addressing Nitrate in California’s Drinking Water, With a Focus on Tulare Lake Basin and Salinas Valley Groundwater.” Perhaps you have heard about this report  already, even read bits and pieces of it, or maybe you have read it in its entirety. The 80-page main report is accompanied by eight technical reports, and all are available at the website groundwaternitrate.ucdavis.edu . To attempt to summarize hundreds of pages in a one-page newsletter article would be impossible but with this article, I will attempt to summarize why this report was generated, some key findings, and some food for thought for us to consider now and in the future.
In 2008, the California Legislature passed a law that required the State Water Resources Control Board (Water Board) to investigate groundwater nitrate levels in the Tulare Lake Basin and the Salinas Valley. Essentially, legislators wanted answers to some questions. How much nitrate is in the groundwater? How did it get there? What can we do to reduce it? How much will it cost? To help answer these questions, the Water Board contracted with UC Davis to get some answers. The UC Davis findings will be included as part of a larger report that the Water Board will provide to the Legislature.
The UC Davis report states that there are two major problems caused by nitrate in groundwater. The first relates to public health because drinking water nitrate levels above 45 milligrams per liter exceed the California Department of Public Health’s level for safety. The study found that 254,000 people in the study areas are at risk of having drinking water nitrate exceeding this level. Cropland was reported to be the source of 96 percent of the human-generated nitrate found in groundwater. The second problem caused by nitrate in groundwater is the cost of cleaning it up. Cleanup measures could include water treatment and/or new wells and could have costs of $20-35 million per year. The report went on to say that addressing the problem will require a multipronged approach of providing safe drinking water, reducing sources of contamination, collecting data, and providing funding to support all of these needs.
Target on agriculture
In the agriculture community, the report was anticipated with apprehension for the obvious reason that it essentially puts a target on agriculture to reduce nitrate loading. The report does make the case for nitrogen needs in agriculture. It states that nitrogen (in plant-available forms like nitrate) is essential for plant growth and global food production, which will need to increase by over 70 percent in the next 40 years according to literature cited. Additionally, nitrogen is part of a balanced, natural cycle in the environment among the atmosphere, soil, plants, animals, and water. The issue at hand is that we interrupt this balance when we add nitrogen to the system, and when excess nitrate-nitrogen is lost to the environment, it sticks around for decades. So, where do we go from here?
One thing we need is a better understanding of crop nitrogen use efficiency (NUE). We need to learn how to optimize timing and rates of fertilizer applications so that a greater fraction of the applied nitrogen is recovered in the harvested crop. Currently, crop nitrogen recovery is estimated at 30-40 percent. Best management practices could increase that value two-fold, but adaptive research is needed to better understand how crop, soil, and irrigation all contribute to nitrogen uptake and loss at different application rates and timings. Certain crop rotations may reduce the need for nitrogen applications, and we must look at varying synthetic fertilizer applications if manure is applied or if groundwater (having some level of nitrate) is used as the irrigation source. Additionally, we must better understand barriers to adopting best management practices, such as costs or risks to crop quality or yield.
As the new Delta crops farm advisor, I anticipate that I will be working, at least in part, on projects related to nitrogen and/or nutrient management. Groundwater in the Delta is a whole other can of worms that will be unique from other areas of the state; nevertheless, like in the rest of the state, we need a better understanding of NUE in Delta crops, under Delta soil and irrigation conditions. This is the food for thought that I will be chewing on and I welcome you to chew on it, too.