Measuring and modeling nitrogen export from cranberry farms

Authors: Kennedy, Casey

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2021
Publication Date: 12/1/2021
Citation: Kennedy, C.D. 2021. Measuring and modeling nitrogen export from cranberry farms. Ecological Applications. 12(12):e03686. https://doi.org/10.1002/ecs2.3686.
DOI: https://doi.org/10.1002/ecs2.3686

Interpretive Summary: Sustainable management of cranberry production requires careful understanding of potential sources of nutrients, which can contribute to off-site water quality problems. An assessment of cranberry bogs contributing to Massachusetts’ Wareham River estuary finds that roughly half of nitrogen losses from cranberry bogs derives from soils, rather than fertilizers and other sources. Strategies that improve nitrogen management in cranberry bog soils are key to protecting downstream water quality.

Technical Abstract: Nitrogen (N) pollution is arguably the single greatest threat to coastal water quality in the United States. Major sources of N to coastal discharge areas include agricultural and residential lawn fertilizers, point and non-point sources of wastewater, and atmospheric deposition. In Massachusetts, the largest agricultural cash crop is cranberries, with about 17% of the global cranberry supply harvested from 5,200 ha of cranbery bog. Adapted to acidic soil conditions, commercial cranberry bogs are fertilized with relatively low amounts of N, ranging from 40 to 58 kg N ha-1 yr-1. However, field observations of N losses from cranberry bogs are generally much higher than modeled contributions from fertilizers and the atmosphere. To reconcile these differences, a third source of N loss that is derived from N stored in the sand and peat soil layers of cranberry bogs, but separate from fertilizers and the atmosphere, is proposed. Solving for the soil term in a fluvial budget equation for a cultivated wetland, soil N loss from cranberry bogs was estimated to be 7.4 ± 3.2 kg N ha-1 yr-1 (mean ± SE). On average, atmospheric deposition contributed 5%, fertilizer 45%, and soil storage 50% of N losses from cranberry bogs. Based on these results, a watershed land use model (NLOAD, Valiela et al. 1997) was used to evaluate sources of N to the Wareham River estuary, a highly eutrophic estuary of Buzzards Bay. NLOAD model calculations indicate that cranberry bogs contribute about one-fourth of the N load to the estuary, but that half of the cranberry bog N load was not related to fertilizer use or atmosphere deposition, but rather to soil storage. As a significant source of N to the estuary, management of N losses from cranberry bogs has the potential to improve water quality in the Wareham River estuary. However, remedial options that focus solely on N fertilizer reductions may miss a major component of N loss from cranberry bogs. As a result, management of drainage waters through increased residence time in secondary holding structures (e.g., ponds) or enhanced naturalization of stream channels should be considered in addition to fertilizer management.