By Jane Sooby
The Second Statewide Agricultural Expert Panel, convened by the State Water Board to advise it on reducing nitrogen (N) contamination of groundwater through the Irrigated Lands Regulatory Program (ILRP), is drawing closer to releasing a draft report for public comment after holding a series of working group meetings in January and February 2026.
During working group meetings, panelists have been provided additional information that they requested including
- Data on farm size differences in reported N applied and crop diversity, Eric Porse and Divya Prakash of University of California Agriculture and Natural Resources (UC ANR)
- Immobilizing soil nitrate using high carbon amendments to reduce nitrate leaching, Joji Muramoto, UC Santa Cruz, UC Cooperative Extension, and UC ANR
- Gaseous N losses from specialty crops in the Central Coast, Stephanie Kortman, California State University Monterey Bay (CSUMB)
Panelists spent the bulk of their working group meeting time hashing out wording and finessing details of their recommendations.
Sneak Preview of Draft Report
The draft report v8 dated February 9, 2026, is the most recent version available. A final draft for public comment is expected to be released later in February. (You can access all expert panel-related documents including draft versions of the report by clicking here and entering Username: agpaneldocs-ftp Password: AgriculturalExpertPanel2!)
The draft report opens with background on nitrogen dynamics, agriculture in California, and the ILRP before responding to the 9 charge questions posed by the State Water Board.
Here are summaries of the panel’s initial responses to the charge questions. Some questions have been paraphrased or edited for clarity as noted.
Targets Versus Limits
Question 1a: Do sufficient data exist to set crop-specific N-related limits that are protective of groundwater quality? (paraphrased)
The panel used the definitions provided by State Water Board staff that a “target” is a non-enforceable standard, while a “limit” is an enforceable standard subject to progressive enforcement. Though the panel refers to “targets/limits” in the text of the most recent draft report, they pull away from recommending limits and instead state, “The panel is comfortable with Regional Boards being required to set targets.” The panel acknowledges that any targets or limits should be set on a regional rather than statewide basis.
Though the draft report states, “The panel agrees that there is a point at which N discharges to groundwater are excessive and Regional Boards should be able to set initial targets/limits that all growers should meet within a reasonable timeframe (3 to 5 years),” a lingering issue is whether the panel will establish an initial “backstop” N limit to immediately stop “egregious” N fertilizer applications or discharges.
Whether targets or limits are set, the expert panel recommends that growers be provided technical assistance to improve their N management and help them comply with the N targets/limits.
Question 1b: What metrics and methodology would be used for developing those limits and what would the limits be?
The panel’s response cites the Irrigation and Nutrient Management Plans (INMPs) required of all irrigated farms and applied N reports submitted annually by growers in the Central Coast and Central Valley water quality control regions, which include data on N applied (A) and N removed (R). By analyzing these data, regulators can identify outliers from the regional average, allowing them to focus outreach on the top N appliers/dischargers.
A new reporting requirement for growers may be forthcoming if the State Water Board acts on the panel’s suggestion that “growers also document how their reported A and R values were determined (fertilizer records, fertilizer sales receipts, product sale records, etc.) so that the quality of the data can be evaluated by third party coalitions and Regional Boards.”
The panel also suggests that growers be incentivized to reduce their A-R values by charging lower fees for those with lower N applications/discharges or by rewarding growers who adopt practices that improve water quality and reduce N leaching.
Question 2: Based on the data and scientific research that is currently available, what series of increasingly protective interim nitrogen-related limits can be set now? (edited)
The panel’s response once more focuses on setting interim targets and using an iterative process to review targets every 3-5 years to see if growers are able to reach them and, if so, to set new targets. The panel notes, “The ultimate goal for the agricultural industry is to achieve nitrate loading that is protective of water quality and as close as agronomically feasible to the operational benchmark [N discharge level that is protective of groundwater].”
New Data Since Original Expert Panel
Question 3: Are there any scientific or technical considerations or advances related to the factors discussed in the First Agricultural Expert Panel’s 2014 Report that the State Water Board should take into account? (edited)
The panel identifies a number of areas in which there have been advances in understanding N dynamics since the first expert panel was convened in 2014, including new root-zone and soil-crop models, advances in understanding nitrate leaching factors, and new data on water-protective best management practices.
A-R Versus A/R
Question 4: Is A-R a scientifically appropriate metric to evaluate and quantify nitrogen discharges to groundwater (either on its own or used in conjunction with A/R)? Are there other metrics that help quantify N discharges? (edited)
The draft report states, “The Expert Panel agrees that A-R is an appropriate metric to evaluate and quantify N discharges to groundwater for regulatory purposes (either used on its own or in conjunction with A/R),” noting that “A/R is not an appropriate metric to assess N discharge, but A/R is an essential metric to assess grower/ranch performance in efficiently using nitrogen.”
Previously, the panel heard from coalition representatives from the Central Valley Region that A/R is used as the primary metric in the region and growers are advised to strive for an A/R as close to 1 as possible. The panel states that A/R may be best used as a means to compare fertilizer use efficiency for growers of the same crop or using the same cropping system.
Fine-Tuning A and R
The panel notes that “The current version of A-R can be improved by including discount factors to A and additional components of R that better reflect grower management practices and account for organic fertilizer and compost N mineralization rates.” Such discounts and credits were specifically remanded from the Central Coast Region’s Ag Order 4.0 by the State Water Board and are not currently in effect. The expert panel’s deliberations suggest that they will recommend that the State Water Board adopt these correction factors for calculating A and R. This point is addressed more specifically in the response to question 7.
The panel also identifies operations that may encounter logistical challenges in measuring R, including those that grow crops that lack an N removal coefficient, “greenhouse production, mixed container nurseries, substrate grown crops, and small growing operations with mixed commodities.” For these situations, the expert panel recommends that growers report A only.
Question 5: Are the INMP summary tables required by the State Water Board’s Eastern San Joaquin Water Quality Order an effective tool for evaluating A and R data? (paraphrased)
The panel confirms that the tables, which are compiled by coalitions, are appropriate for estimating N discharge to groundwater and sets forth an extensive list of data that coalitions should summarize for each crop or cropping system, suggesting that “this level of detail in reporting may be an appropriate requirement to set for all California agricultural regions.”
The panel also suggests that INMP summary tables “add simplified information on the predominant soil series (e.g., coarse vs. fine grained soils, well- or poorly drained, with or without hardpan, saline/sodic issues).” If adopted by the State Water Board, this recommendation may result in additional reporting by growers unless coalitions are able to fill in soil series data on their behalf.
Acreage Data: Confidential or Public?
Over the course of the expert panel’s deliberations, some public commenters have noted that the Central Valley Region doesn’t provide acreage data and have requested that these data be made public so that stakeholders are able to independently analyze the effectiveness of ILRP in protecting groundwater from N leaching. The Central Valley Region’s rationale for not revealing acreage data is that it protects grower confidentiality and thus encourages accurate reporting. The draft report addresses this issue and recommends “that each region develop data privacy and transparency frameworks” and that acreage data be reported in acreage categories (<1 acre, 1 to < 10 acres, 10 to < 100 acres, etc.) to prevent identification of specific operations based on their acreage.
Should Limits Be Placed on Mineral Fertilizer Application Rates?
Question 6: Should mineral N (AFER) application limits such as those developed by the Central Coast Regional Water Board in Ag Order 4.0 be used to set interim limits to protect groundwater? (paraphrased)
The panel states that targets/limits on mineral fertilizer application rates “have questionable benefits” and recommends that any targets or limits focus on A or A-R. The panel notes that A includes not only N from mineral fertilizers but also from organic fertilizers, compost, and irrigation water. They conclude that “AFER alone provides an incomplete assessment of the risk of N losses.”
N Discounts and Credits
Question 7: Do the N discount and credit factors included in the Central Coast Region’s Ag Order 4.0 allow for full accounting of the potential for N discharge to groundwater? These include discount factors to A (compost [ACOMP], organic fertilizer [AORG]), R credits (RSCAVENGE, RTREAT, and ROTHER), and excluding nitrogen in irrigation water from the calculation of total nitrogen applied. (paraphrased)
The panel asserts that the factors in Ag Order 4.0 are grounded in science and are “practical policy measures” that more accurately estimate N mineralized from organic fertilizers and compost. In addition, these factors incentivize growers to adopt practices such as winter cover cropping, use of high carbon amendments, and use of irrigation water nitrate as a crop N source.
The panel also notes how the Central Valley Region uses the CV-SWAT model to analyze INMP-reported data and estimate field-level potential N discharge to groundwater.
The panel cites new data that justifies expanding the definition of the metric RSCAVENGE to include additional practices including planting fall cover crops or “low residue” cover crops. In addition, they suggest adding two new factors, RGASEOUS to account for N that is denitrified or volatilized and ADEPOSITION to account for atmospheric N deposition.
On the topic of allowing growers to not report N in irrigation water when calculating A, the panel expresses support for “pump and fertilize” and suggests that the N in irrigation water be reported but not used for assessing compliance with any A-R targets/or limits established by the regional board. They recommend streamlining the three compliance pathways set forth in Ag Order 4.0 into a single pathway that caps total credit for N in irrigation water to 200 lb N/acre/year or total crop N removal over the year, noting that the credit could be increased in the future as growers gain more experience with accounting for irrigation water N in their nutrient budgets.
Should Small Farms Be Regulated Differently?
Question 8: Is there enough data and scientific research to conclude that small and/or small diversified farms are operated in a fundamentally different manner that results in a reduced water quality impact compared to larger farms, on a per acre basis? If yes, what criteria could be used to identify the operations that have reduced water quality impacts?
While acknowledging that farm scale does not necessarily correlate with the farm’s risk to groundwater quality, the panel recommends creation of a category “reduced-risk small farm” that would meet many criteria associated with lower risk of nitrate leaching. The panel presented three overarching categories of small farms in California and discussed the relative risk of nitrate leaching for each.
- Small-acreage monocultures of major California commodities such as grapes, almonds, pistachios, walnuts, citrus, lettuce, and strawberries. The panel notes, “these small-acreage farms are unlikely to demonstrate a reduced water quality impact based on acreage alone” while also pointing out that small-acreage certified organic or regenerative farms that produce these commodities may implement practices associated with a reduced risk of nitrate leaching.
- Small-acreage plots of niche or emerging crops such as such as specialty Asian vegetables and herbs, agave, and others. The panel notes that neither research-based fertilizer recommendations nor N-removal coefficients may yet be available for these crops and suggests that “alternate reporting requirements” be developed until they are.
- Small-scale diversified farms, defined as having more than two crop rotations per acre on a maximum of 80 acres, that utilize a “whole-farm” approach to nutrient management such as building soil organic matter over time, planting winter N-scavenging cover crops, reducing input applications, and improving irrigation efficiency with drip systems. The panel suggests that these may be classified as “reduced risk” operations that are eligible for alternate reporting requirements such as those set forth in the Eastern San Joaquin Water Quality Order.
Acknowledging that the regulatory burden for small farms is higher than for larger farms, the panel suggests that regional water boards develop simplified INMP reporting requirements for small farms that don’t fall into a lower risk category. “An average value of A and R for diversified small farms or at a minimum reporting A and indicating best management practices used could greatly reduce the regulatory burden for these growers,” the panel writes.
The Special Case of Container-Grown Nurseries
During its deliberations, the panel heard from nursery producers about the challenges they encounter in complying with agricultural orders because they grow a diverse range of ornamental plants in containers and discharge very little water to groundwater. In addition, the substrate in which the plants grow is sold along with the plant, which makes it difficult to calculate an accurate R value. The panel suggests that nursery producers who use best management practices such as lining retention ponds and drainage ditches and reusing drainage water for irrigation may qualify them for reduced regulatory reporting.
Potential Exceptions to the Precedential Requirements
Question 9: Is there enough data and scientific research that would support any other exceptions to, or alternative methods for complying with, the precedential nitrogen management requirements in the Eastern San Joaquin Water Quality Order? (edited)
The panel identifies five crops and cropping systems that may be candidates for exemption from or alternative compliance pathways for the regional ag orders:
- Wine-grape vineyards
- Alfalfa
- Non-fertilized pasture (already exempted in the Central Valley Region 5)
- Nursery and floral production
- Organic and “regenerative” farms that use management practices associated with low nitrate leaching risk
The panel also acknowledges that some regions, such as the Imperial Valley, lack wells to access groundwater and currently do not use groundwater for any beneficial use and should be subject to alternative compliance pathways.
Best Management Practices
Following their responses to the charge questions, the panel presents a section describing best management practices for effective irrigation and nutrient management, including
- Conduct comprehensive soil and plant testing to guide N fertilizer application
- Adopt integrated irrigation scheduling supported by decision tools and soil moisture sensing to improve water and N use efficiency
- Improve irrigation water delivery systems through targeted upgrades and automation to reduce deep percolation and nitrate leaching
- Account for nitrate contributions from irrigation water using crop-specific evapotranspiration (ETc-based) N accounting
- Follow crop-specific N fertilization guidelines where available
- Utilize cover crops during fallow periods to reduce nitrate leaching and improve N retention
- Apply high carbon organic amendments during winter fallow to reduce nitrate leaching through microbial immobilization
- Incorporate N scavenging rotational cash crops to reduce residual soil nitrate losses
- Select crop varieties with higher N use efficiency to improve productivity and reduce nitrate losses
- Adopt enhanced efficiency fertilizer technologies to improve N use efficiency and reduce nitrate leaching
- Implement denitrification bioreactors where appropriate to reduce nitrate losses from agricultural drainage
- Explore emerging and novel technologies as complementary strategies for reducing N losses including microbial inoculants
- Variable-rate N application
Outreach, Research, and Models
The draft report also presents recommendations on outreach, technical assistance, and research needed to better understand N leaching dynamics. The text ends with a detailed section describing how hydrological models are used to assess well nitrate contamination risks from agriculture.
What’s Next?
The next expert panel meeting is scheduled for March 11, 2026. If the panel is able to finalize its draft report by February 22, the report will be put out for public comment around February 24 and the March 11 meeting will be a listening session open to public comment on the draft report. If the panel still needs time to work on their report, the March 11 meeting will be a working group meeting. For the latest information, consult the Second Statewide Expert Panel’s website: https://www.waterboards.ca.gov/water_issues/programs/agriculture/2025-expert-panel.html
