Panel members debated whether to rely on a fertilizer-only application limit or to retain A minus R (applied minus removed) as the principal metric for estimating nitrate risk to groundwater. Daniel Geisler framed Question 6 by asking whether the panel should recommend a two-step approach (application limits plus A minus R) or focus only on fertilizer application.

Several technical experts — including Hannah Waterhouse and Richard Smith — said A minus R better captures the full set of nitrogen inputs (fertilizers, irrigation water nitrogen, and organic amendments) and helps account for field-level removal. Panelists acknowledged that fertilizer-only metrics are simpler to implement and might help flag the highest applicators, but they repeatedly emphasized that fertilizer-only limits risk undercounting sources such as irrigation water and organic amendments unless accompanied by robust data and credits.

On Question 7, the panel examined discount factors for organic amendments (compost, manures, organic fertilizers) and for practices such as cover crops. Thomas Harder and other presenters reviewed empirical studies and regionally used methods (for example, the Central Coast and CBSwap approaches). Panelists said discount factors are defensible where empirical, region-specific studies exist (for example, short-term mineralization experiments and cover-crop trials) but cautioned that many regions lack long-term data and that discount factors should be conservative and regionally tailored. The panel recommended additional targeted research (longer-term mineralization studies, municipal/producer reporting at town-level granularity) and that staff consider complementary fertilizer-focused tables where data support them, while keeping A minus R as the principal performance metric.

Several members asked staff to provide municipality-level and cultivator-level data (particularly in the Central Valley) to assess how percentile-based thresholds would map onto growers and to avoid unintended consequences for small or diversified operations. Panelists agreed to draft an updated written response that emphasizes A minus R, recommends research and data-collection priorities to improve discount-factor estimates, and proposes limited, regionally tested fertilizer tables as a supplemental enforcement or screening tool.