State Water Board expert panel debates crop-specific nitrogen limits; panelists favor regionally tailored thresholds and multi‑year averages

Members of the State Water Resources Control Board's statewide agricultural expert panel working group spent most of a working meeting debating whether groundwater‑protective nitrogen thresholds should be set on a crop‑by‑crop basis or instead by region and aggregated source area.

Panel chair Daniel Geisler, Cooperative Extension specialist in Nutrient Management at UC Davis, opened the discussion by asking whether the data presented so far support crop‑specific limits and what additional information the panel should request. "We should probably have a brief look or an opportunity to talk about our general impression of the data," Geisler said as the group moved into the charge questions.

Why it matters: any numeric limit will affect how growers measure fertilizer use and reporting, and, if tied to enforcement, could trigger costly penalties. The panel repeatedly returned to the central public‑health benchmark of 10 milligrams per liter nitrate (the drinking‑water standard) and the practical question of what loading on the landscape translates to that standard in groundwater.

Most panelists said crop‑specific, single‑season…