Researchers say container nurseries leach less nitrogen than INMP assumptions; recommend BMPs and targeted monitoring

Presentations from two UC Cooperative Extension advisers gave the panel new data and practical recommendations for nursery operations.

Bruno Piton presented a mass-balance study on container-grown Crepe Myrtles that tracked nitrogen inputs (controlled-release fertilizer) and outputs. He reported roughly 5% of applied nitrogen was in plant tissue at sale, 56% remained in substrate, 6% was captured in off-site runoff (potentially reusable), ~30% was lost to gaseous emissions (denitrification) and about 3% leached below the nursery bed soils. Piton concluded that translating INMP removal calculations directly from field crops to container systems risks overestimating potential leaching from nurseries.

Gerardo (presenting as "Jerry") Spinelli described regional nursery practices in San Diego and Los Angeles counties and emphasized workable, site-level measures: lining ponds and ditches, installing bypasses to separate irrigation-season reuse from stormwater, capturing and repumping pond water for reuse, and building sedimentation/holding ponds. He noted strong economic incentives in Southern California (very high water costs) that make capture and reuse practicable for many growers.

Panelists asked how a nursery could demonstrate superior performance; presenters suggested infrastructure (flow meters, flumes, lined ponds) and documented reuse practices but acknowledged monitoring and mass-balance studies are costly. Bruno offered to share the study details and sample application rates with staff for distribution.

Takeaway: for container nurseries, the presenters advised a focus on BMPs and targeted infrastructure investments rather than onerous per-crop removal reporting; where monitoring is needed, clearly defined pilot studies and technical assistance should be supported.