Two experts presented new and summarizing data on nitrogen dynamics in nursery (vivero) production and urged the panel to treat nurseries differently from field crops when developing reporting or limits.

Bruno Pichón described controlled mass-balance experiments on containerized nursery systems: in one study he reported approximately 5% of applied nitrogen recovered in plant tissue, about 56% remained in potting substrate, roughly 6% of the applied nitrogen appeared in leachate that could be captured and recycled, and about 30% was estimated to be emitted as gaseous nitrogen. Bruno warned that these numbers are system-specific (substrate type, container size, temperature, and fertilization method) and recommended management best practices (capture and reuse of leachate, adoption of controlled-release fertilizers or adjusted fertigation) and greater sampling before imposing field-crop-style accounting rules on nursery operations.

Jerry (UC Cooperative Extension) reviewed region-specific practices in San Diego and Los Angeles: strict local runoff controls, requirements to keep irrigation water on property, and widespread adoption of lined retention ponds or reuse systems in some counties. He noted large heterogeneity among nursery operations (container sizes, crop rotations, irrigation methods) and said that standardized monitoring (flow meters, capture systems, and targeted soil or leachate testing) would be the most defensible way to demonstrate superior performance.

Panelists asked whether simple metrics (sales-based fertilizer per area) would be useful; presenters cautioned that nursery crop diversity and container systems make such comparisons unreliable. The panel agreed that nurseries may merit a distinct reporting pathway and asked staff to incorporate nursery-specific guidance and data needs into the draft report.