A California groundwater study focused on nitrate levels has placed the agriculture industry – and more specifically the dairy industry – in the spotlight. One of the key findings in the study points the finger directly at agriculture. Fertilizers and animal wastes applied to cropland are by far the largest regional sources of nitrate in groundwater, the study said.

Nitrate contamination of groundwater will increase, the study added, as nitrogen from fertilizer, manure and other sources applied in the last 50 years continues to percolate downward and flow toward drinking-water wells.

The state health department has determined that maximum nitrate level in drinking water is 45 ml per liter. In the two areas studied, 254,000 people are at risk for nitrate contamination of their drinking water.

Nitrate loading reduction is possible, the study said, but there is a cost. Larger reductions of nitrate in groundwater would cost substantially.

Fees for nitrogen fertilizer use and tighter restrictions on manure applications are suggestions, but mitigation measures could take time – years to decades – before reduction of nitrates are realized, the study said.


In the short term, soil sampling and shallow groundwater testing could provide proof that measures taken are effective.

Commissioned by the state’s water resources board and conducted by University of California researchers, the study, released in March 2012, focused on the Tulare Lake Basin and Salinas Valley, which includes 40 percent of the state’s irrigated crop land and more than half of the state’s dairy herd.

Groundwater hydrologist and UC researcher Thomas Harter said that of the 420,000 tons of nitrogen applied by agriculture annually, about a third is harvested as crops, 10 percent is lost in the atmosphere and half – the primary concern – moves toward groundwater.

At a well-attended May 3 workshop in Parlier, UC researchers answered questions about the study and listened as stakeholders shared their perspectives on the study.

Porterville dairyman Tom Barcellos pointed out – as did others in the audience – that dairy has been doing its part to prevent groundwater contamination and is working toward higher efficiencies in nitrogen applications.

Barcellos, known for his conservation tillage practices, said tests on his fields showed low levels of nitrates below the root zone.

“We learned 10 years ago about using flow meters and blending. We’ve done a lot to manage nutrients,” he said.

Agriculture does want to do its part, he said, but some options in the study are worrisome to dairy producers who already are working on very thin margins.

“This problem has been years in the making; it won’t be easy or fast to solve, “ Barcellos said. “Let’s keep moving forward instead of making mandates that will drive us out. We have the same goal.”

Dennis Keller, an engineer and consultant for water systems in the four counties that comprise the basin, pointed out there are success stories of nitrate remediation in the Tulare Lake Basin.

Tulare County Supervisor and citrus grower Allen Ishida asked that, before there are more regulations or fees, test wells be used to determine a baseline for nitrate contamination.

It is important to note, he added, that current cultural practices such as drip irrigation may also play a part in keeping fertilizers from leaching into groundwater.

UC researcher Kristin Dzurella said the study has identified a number of best management practices to reduce nitrogen leaching.

Improved storage and handling, matching water rates, timing and placement with soil types are examples.

It is also important to determine the fertilizer value of applied manure to avoid overfertilization. The recommendations, she said, can increase nitrogen efficiency to 60-80 percent. Some practices are already in place on dairies and farms, she noted.

But there are roadblocks to adoption, Dzurella said. Those include logistics, education and costs.

“Significant costs may reduce crop areas and no one wants to see that,” she said.

Investment in farmer education is important. Supporting development of nitrogen accounting methods, so farmers know if they are improving, would also be helpful, Dzurella said.

Addressing groundwater nitrate contamination requires action on four fronts. Safe drinking water for affected residents must be supplied, sources of nitrate contamination must be reduced, groundwater monitoring and assessment of drinking water must continue and revenues must be found to help fund solutions.

The nitrate contamination issue is not confined to just California. Many Western states have similar problems and are developing programs to avoid contamination.

New Mexico hydrologist Jay Lazarus, who works on groundwater contamination issues, said many of today’s problems are the result of past practices. Lagoon seals that did not work are one example.

Lazarus, owner of Glorieta Geosciences, Inc. of Santa Fe, said dairy operators should adhere to best management practices and all terms of their nutrient management plans to prevent nitrate leaching.

Accurate forecast of nutrient applications and amounts will assist producers in keeping within the bounds of their NMP, he noted. Farmers need to be able to predict nutrient application amounts and when and where they will be applied, Lazarus said.

Effects of mitigating practices by dairy producers or farmers will take time – many years to decades – to show up in production wells, said Harter.

In the meantime, the agriculture industry can look at nitrogen balances in soil samples and shallow groundwater monitoring to document improvements long before they show up in production wells.

Click here to read the entire groundwater nitrate study, by the Center for Watershed Sciences, University of California – Davis. PD

Parsons is a freelance writer based in Ducor, California.

PHOTO: Representatives from stakeholder groups led a panel discussion about a recent California groundwater nitrate study. Panelists included, from left, Dennis Keller, engineer and consultant; Laurel Firestone, representing affected small communities; Tom Barcellos, dairy producer; Paul Boyer with Self Help and Tulare County Supervisor Allen Ishida. Photo courtesy of Cecilia Parsons.