A state-appointed panel of agricultural and academic experts is urging California regulators to move toward region-specific limits for on-farm nitrogen use, as groundwater contamination from farming remains a longstanding and widespread concern.
The draft report released Monday by the Second Statewide Agricultural Expert Panel recommends establishing crop-specific targets or limits on nitrogen applications in areas where sufficient data exists, while allowing more time for other regions to develop the necessary scientific foundation.
The report will help guide future updates to the Irrigated Lands Regulatory Program, the state’s primary framework for controlling agricultural runoff and groundwater pollution. The program, launched in 2003 and later expanded to include groundwater protections, regulates discharges from millions of acres of irrigated farmland.
At issue is nitrate contamination — largely driven by fertilizer and manure use — that has built up over decades in key agricultural regions like the Central Valley. Studies have found that fertilizer runoff is a dominant source of nitrate pollution, with impacts to drinking water affecting hundreds of thousands of residents, particularly in rural communities reliant on wells.
The expert panel reaffirmed the state’s reliance on nitrogen “mass balance” — comparing nitrogen applied to nitrogen removed by crops — as a practical metric for evaluating grower performance and potential groundwater impacts.
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But the panelists stressed that California’s agricultural diversity makes uniform statewide limits impractical. Instead, they recommend regional water boards tailor nitrogen targets to local cropping systems, soils and hydrology.
The panel also emphasized a phased approach. Rather than requiring immediate compliance with drinking water standards, such as a 10 parts per million nitrate threshold, regulators should adopt interim targets that gradually tighten over time while remaining agronomically feasible.
The recommendations build on more than two decades of evolving regulation. Since the Legislature first directed water boards to regulate agricultural discharges in 1999, the program has expanded to require detailed reporting, including farm-level nitrogen management plans and monitoring of drinking water wells for contamination.
Growers today must track nitrogen inputs and outputs and, in vulnerable areas, develop certified irrigation and nitrogen management plans to reduce leaching into groundwater.
Still, regulators and researchers acknowledge significant uncertainty remains. The panel highlighted ongoing data gaps and called for expanded monitoring, standardized reporting and greater use of modeling tools to better link farm practices with groundwater outcomes.
The broader policy challenge is balancing environmental protection with the realities of California agriculture, which produces more than 400 commodities and depends heavily on fertilizers to maintain yields.
Comments on the draft report are open through April 30, with a final version expected later this year. The State Water Resources Control Board will host a workshop on the findings on April 10.
