A base layer of ferrous sulfate-amended pine bark reduces phosphorus leaching from nursery containers

Authors: Shreckhise, Jacob - Jake; Altland, James

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2024
Publication Date: 4/6/2024
Citation: Shreckhise, J.H., Altland, J.E. 2024. A base layer of ferrous sulfate-amended pine bark reduces phosphorus leaching from nursery containers. Agronomy. https://doi.org/10.3390/agronomy14040757.
DOI: https://doi.org/10.3390/agronomy14040757

Interpretive Summary: Phosphorus (P) fertilizers applied to container-grown nursery crops readily leach through pine bark-based substrates and can subsequently runoff and contribute to surface-water contamination. ARS scientists from McMinnville, TN and Wooster, OH discovered a novel method for reducing the amount of P draining from nursery containers. They showed that adding a shallow (4-7.5 cm) layer of pine bark-based potting media containing ferrous sulfate to the bottom of nursery containers decreased the amount of P draining from those containers by 22-73%, with greater reductions corresponding with higher amounts of ferrous sulfate added. This approach is unique in that the ferrous sulfate, a widely available water-soluble iron fertilizer, coats the pine bark particles with iron which improves the P retention capabilities of the pine bark itself. This scalable and relatively inexpensive best management practice can be adopted by both small and large nursery operations to minimize their contributions to agricultural P runoff--a known source of P leading to toxic algal blooms in receiving waters.

Technical Abstract: Phosphorus (P) fertilizers applied to container-grown nursery crops readily leach through pine bark-based substrates and can subsequently runoff and contribute to surface-water contamination. The objectives of this research were to determine the effect of adding a layer of FeSO4·7H2O-amended pine bark (FSB) to the bottoms of nursery containers on P leaching charac-teristics. Phosphorus and iron (Fe) leaching in response to FSB layer height (4 or 7.5 cm), FeSO4·7H2O rate (0.3, 0.6, or 1.2 kg·m–3 Fe) and form (i.e., granular versus liquid) used to formulate the FSB layer, and the inclusion of dolomite in the FSB layer were also investigated. Fifteen- and 19-week greenhouse studies were conducted in which 2.5-L nursery containers containing the FSB layer treatments below non-amended pine bark substrate were fertilized with 199 or 117 mg P from a soluble or controlled-release fertilizer, respectively. Leachate resulting from daily irrigation was collected and analyzed for P and Fe weekly. All FSB treatments leached less P than the control (non-amended pine bark only), with P reductions ranging from 22% (4 cm FSB with 0.3 kg·m-3 Fe) to 73% (7.5 cm FSB with 1.2 kg·m-3 Fe). Phosphorus leaching decreased linearly with increasing Fe rate or layer height. The amount of Fe that leached from containers with FSB was <5% of that applied, regardless of Fe rate. Granular- and liquid-applied FeSO4·7H2O with or without dolomite were equally effective at reducing P leaching. Adding 0.6 kg·m–3 Fe to the bottom 500 cm3 of pine bark increased P adsorption by 0.053 mg·cm–3 P, which equates to 17.9 mg P adsorbed per gram of FeSO4·7H2O added. Results from this research suggest including an FSB layer in the bottom of nursery containers is an effective strategy for reducing P runoff from container-based nursery production sites.