Panelists at the State Water Resources Control Board expert-panel meeting examined how to measure and manage fertilizer nitrogen applied to farmland to protect groundwater, debating whether regulators should set area-based targets, crop-specific limits or process-based goals and what data and tools are needed to implement any standard.

Panel moderator Daniel Kaisler opened the session and staff explained the schedule and upcoming public-listening events. Panelists focused on “A–R” accounting — the balance between nitrogen applied (A) and nitrogen removed (R) — and on whether goals should be framed as a hard limit or as an objective and monitoring framework. Panelist Richard (panelist) cautioned against prematurely adopting strict numerical caps and urged a focus on process and implementation, saying in Spanish, “yo quisiera vernos que utilicemos más bien un enfoque en vez de un límite.”

Why it matters: regulators use A–R and related tools to estimate how much applied nitrogen could leach to groundwater. The panel’s recommendations will inform how regional water boards and coalitions monitor farms, set targets, and design outreach, incentives and enforcement to reduce nitrate pollution in groundwater used for drinking water.

Panel discussion and technical detail

Panelists described three broad approaches: (1) an area- or field-based metric (for example, pounds per acre per year); (2) crop-specific per-crop targets; and (3) process-based, model-driven methods that use field reports plus hydrologic modeling (for example, CV‑SWAT/CVSWAT and CropManage). Several panelists favored area- or field-based metrics with multi-year averaging rather than per-harvest limits, saying a one-year or per-crop approach can misrepresent seasonal and multi-crop systems in California.

Some participants suggested specific starting points discussed in the meeting: an “objective” on the order of 50 pounds of nitrogen per acre per year was proposed as a regionally illustrative figure, and spatial accounting units of roughly 40 to 160 acres were discussed as plausible management scales for field-level evaluation. Panelists emphasized these numbers as discussion points, not final regulatory values.

Soil sampling and agronomy

Erick (soil-lab expert) described standard soil-sampling protocols used in his work and summarized how those data inform fertilizer decisions: “como regla general, si hay 200 libras presente en esos 2 pies superiores ... Mi consejo para un cultivador sería no aplicar más nitrógeno,” he said, explaining that sampling multiple cores (standard UC protocol: ~12 cores to 12 inches, homogenized, KCl extraction and lab analysis) can identify residual soil nitrate and help growers avoid unnecessary fertilizer. Erick and others stressed that residual nitrate, irrigation-source nitrate and mineralization from residue and cover crops make A–R accounting dynamic and regionally variable.

Cover crops, mineralization and regional differences

Multiple panelists said cover crops can transfer nitrogen residues into subsequent crops via mineralization and that those effects are measurable but regionally dependent. Presenters showed a case where substantial portions of available nitrate after a cover crop were lost to leaching when fields underwent intensive leaching or salinity management, underscoring that region, climate and management alter how much previous-season residue contributes to next-season nitrogen available to crops.

Modeling and data integration

Panelists urged combining grower-reported A–R accounting with process-based models (e.g., CV‑SWAT/CVSWAT, CropManage) so regional coalitions can estimate likely leaching rather than relying on a single metric alone. Several speakers recommended anonymized but accessible coalition data to build regional baselines, while recognizing coalition data availability varies across regions (Central Valley, Central Coast, Imperial, Salinas, Coachella).

Implementation, outreach and incentives

Participants repeatedly said education, incentives and technical assistance will be essential for growers to change practices. Multiple experts noted that while agronomic tools and soil testing can reduce applications, growers face economic risk if they under-apply and lose yield; therefore, incentive programs, demonstrations, and near-term technologies (slow-release fertilizers, nitrification inhibitors, improved irrigation efficiency) were discussed as ways to accelerate change.

Next steps and procedural actions

The panel set teams of two to draft responses to specific panel questions and asked staff to assemble presentations and a list of additional invited experts for the October 31 session and subsequent public-listening events. State staff (Ana Elisa Quijara) requested a draft of the panel report for internal review in December if possible, with a 30‑day public comment period ahead of a January plenary; staff noted the panel may schedule an additional workshop or finalize timing to allow public review.

Ending

Panelists agreed on two enduring themes: region-specific solutions will be necessary, and combining field-level data (A–R), soil testing and process-based modeling will give the best basis for regulatory decisions. The panel will continue technical presentations (including CV‑SWAT) at the October 31 session, finalize drafting teams, and aim to circulate a draft report for public comment ahead of a January plenary where the panel will consider final recommendations.