State Water Resources Control Board expert panel focuses on data gaps and approaches for nitrogen limits in agriculture

Panel Chair Daniel Geisler convened the State Water Resources Control Board’s second expert panel on agriculture to continue developing technical recommendations on agricultural nitrogen and groundwater protection, focusing strongly on the first charge question about whether to adopt crop‑specific application limits, discharge limits tied to groundwater protection, or other target approaches.

Panelists agreed the core task is technical: identify where data exist, where gaps remain and what targeted expert input the panel needs to evaluate limits versus objectives. Several panelists said existing data are sufficient in some regions to evaluate regionally tailored limits but not adequate statewide for crop‑by‑crop numeric limits. Thomas Harder, a UC Davis cooperative extension faculty member and hydrologist, emphasized the role of groundwater mixing and travel time in interpreting field‑level measures and said “it makes more sense to consider multi‑year totals and landscape scales rather than a single crop in a single season” when the goal is protecting drinking‑water wells.

Panelists discussed concrete data and modeling needs. Michael Kahn (cooperative extension, irrigation/water resources) and Richard Smith…