Growing Attention to ‘Nitrates’: A Call to Action for California Dairies

Thomas Harter

By J.P. Cativiela

California dairies play a critical function, providing more than a fifth of the nation’s milk and jobs for hundreds of thousands of Californians. But dairy farmers also have an important role to play in protecting the future of the Golden State’s water supplies.

That’s the message of Dr. Thomas Harter, a University of California Davis hydrologist and one of the leading experts on the vast underground sea of water that supports the Central Valley, one of the world’s leading agricultural regions and home to 85 percent of the state’s dairy farms.

“California’s most productive agricultural regions have a drinking water problem from nitrate contamination,” Harter recently told the California Dairy Research Foundation. “The overwhelming source of this, more than 90 percent, is from agricultural fertilizers and this of course includes animal waste such as dairy manure.”

Although agriculture in general and dairy farmers specifically have improved their management practices in recent decades, more can and must be done to prevent impacts to future drinking water supplies, Harter said. This is because the same water that farmers depend on to produce food for millions also is an important source of drinking water for much of the state’s population.

What is nitrate and why do we care?

A simple and common molecule, nitrate (NO3) comprises one atom of nitrogen and three atoms of oxygen. An important plant nutrient, it has also become a common component of agricultural fertilizers such as ammonium nitrate. Plants absorb nitrate from soil and water through their roots, so nitrates are also common in foods, such as green beans, carrots, squash, spinach, beets and lettuces.

While small amounts of nitrates in food usually don’t pose a problem for most humans, high levels are associated with elevated levels of methemoglobin in the blood, according to the U.S. Environmental Protection Agency. Partly due to the nature of their developing digestive systems, infants are considered susceptible to methemoglobinia, or blue baby syndrome, a rare and potentially fatal disease that can be caused by nitrates or other factors, including genetic disorders. As a result, EPA’s health standard of 45 parts per million nitrate in drinking water is designed to protect infants.

How does nitrate get into drinking water?

Farming is essentially a “leaky” enterprise, Harter explains. Farmers plant their crops in a variable range of sandy, loamy and clay soils of the Central Valley, applying water and fertilizer – including dairy manure – to help plants grow and thrive.

While it would be nice if all the water and fertilizer ended up in the plants, that just doesn’t happen and probably isn’t possible.

“Hopefully most of the nutrients from manure go back into the corn and other crops, but we know this is a leaky system – it’s not a closed system,” Harter said.

Some of the water seeping below ground carries nitrate with it. Nitrate can partly break down to escape as harmless nitrogen gas. But some of it remains dissolved in the water, to be extracted later from wells. After many decades of farming and use of rural septic systems in parts of the Central Valley, up to 1 in 10 wells – especially in smaller communities – now exceed federal health standards for nitrate.

Can agriculture and dairies reduce nitrates entering groundwater?

With more than 90 percent of ongoing nitrogen loading in the Central Valley coming from agriculture, it’s clear that farmers must do they best they can to minimize fertilizer leaching to groundwater. Pointing out that use of both groundwater and nitrogen fertilizers are necessary worldwide to feed billions, Harter also sees an opportunity.

“Nitrate contamination is a common problem among the world’s agricultural regions,” Harter said. “For California, addressing nitrate in drinking water supplies presents an opportunity to provide leadership at a time when food and fiber production must nearly double to feed the world by 2050.”

Harter suggests that farmers could achieve 60 to 80 percent efficiency in using fertilizer, but have not yet reached that target. Doing so would not only better protect water resources, but could save fertilizer costs in the future and possibly lead to other economic benefits such as improved water use efficiency and crop yields.

What ideas should dairy farmers consider?

Central Valley dairies are already under the nation’s strictest water quality regulations. These include management plans specifically designed to limit nitrogen fertilizer loading to plant needs, along with testing of plant tissue, soil and manure to support proper use of dairy manure and fertilizers. Dairies are also monitoring water quality by sampling wells to track progress.

While these are important steps, Harter points out that a third of the nitrogen fertilizer applied in the southern half of the Central Valley comes from dairy manure. He believes dairy farmers could benefit from further investment in research, outreach and education aimed at better utilizing this abundant resource. These include:

  • More investigation and utilization of so-called “pump-and-treat” techniques, in which nitrate-containing groundwater is pumped to be used for irrigating and as part of the fertilizer regime for farming, thus returning the nitrates into the system and reducing the overall nitrogen load.
  • Development and adoption of improved management tools for fertilizing and irrigating with manure, to improve decision-making related to fertilizer and irrigation application timing and rates.
  • Research and development into improved techniques for storing, transporting and even transforming manure through innovative processes. Doing so could help turn manure into a desirable replacement for synthetic fertilizers.

Harter’s key message: Reaching clean water goals require working together

One of Harter’s key messages is that all Californians, including dairy farmers, need to act to preserve and protect groundwater.

“This problem has developed over many decades and will also take a lot of time and hard work to fix,” he said. “But action is needed. I think dairies know they must be part of this and it’s encouraging to see people talking more about this important issue and beginning to plan for a future that protects both are vital agriculture industry and our groundwater resources.”

About the author: Cativiela is program coordinator for Dairy Cares, which works jointly with the California Dairy Research Foundation to communicate and increase awareness about the progress of California dairy families on environmental and other sustainability issues.