Influence of FGD gypsum on P loss from a horticultural growth medium

Authors: Watts, Dexter; Runion, George; Torbert, Henry - Allen

Submitted to: Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2021
Publication Date: 7/17/2021
Citation: Watts, D.B., Runion, G.B., Torbert III, H.A. 2021. Influence of FGD gypsum on P loss from a horticultural growth medium. Horticulturae. 7(7):199. https://doi.org/10.3390/horticulturae7070199.
DOI: https://doi.org/10.3390/horticulturae7070199

Interpretive Summary: Phosphorus entering streams, creeks, lakes, and rivers can lead to environmental problems. Thus, effort is being made to reduce P loss from agricultural sources. Growing nursery crops in containers can lead to P loss because the potting media used is porous which promotes drainage. It is believed that gypsum can be used to adsorb the P in the media, thereby curbing P loss. Therefore, a leaching study was performed to evaluate the use of gypsum amendments to a potting medium as a management practice to reduce P loss. Containers were watered over a course of three months and the amount of P lost with water dripping from the containers was measured. Adding gypsum to the potting medium reduced the amount of P leaving the containers. The amount of P lost decreased as the amount of gypsum applied increased. In addition, the gypsum was either mixed with the growing medium or placed at the bottom of the containers. Mixing the gypsum with the medium was the most effective and easiest means of incorporation. Results from this study suggest that gypsum can be used to reduce P when applied to horticultural potting media.

Technical Abstract: In response to agriculture’s contribution to surface water quality, considerable effort is being made to identify hotspots and develop best management practices to reduce the potential for nutrient losses. Containerized horticultural production is believed to be a significant contributor of nutrient loss to the environment resulting from the widespread use of high porosity soilless media. Incorporating gypsum with media in horticulture containers may mitigate P leaching losses. To evaluate the efficacy of using gypsum as a media amendment for controlling P leaching, flue gas desulfurization (FGD) gypsum was added to a standard horticultural growth medium at 0, 2.5, 5, 10 or 15% (v/v). The FGD gypsum was either mixed with the growing medium or placed at the bottom of the containers. A fast-release or a control-release fertilizer was added top-dressed as the fertility source. The greatest losses of P to leaching occurred with the fertilizer only treatments (no gypsum). Dissolved reactive P (DRP) losses were highest on the initial day of measurement for the fast-release fertilizer and then decreased rapidly. There was a delayed release of DRP from the controlled-release fertilizer source. Increasing rates of FGD gypsum addition resulted in decreasing DRP leaching concentration loss and load. The FGD gypsum decreased leachate DRP concentration loss by a maximum of 75%, with an average decrease of 46%. Mixing the FGD gypsum with the medium (an easier/less expensive means of incorporation) was most effective with the fast-release fertilizer. These preliminary results indicate that less gypsum may be needed to reduce P loss from fast-released fertilizer as opposed to control-release fertilizer. Reductions in DRP losses were observed over the course of the entire experiment with the addition of gypsum. This suggests that the FGD gypsum remained effective in reducing DRP loss throughout the duration of the experiment.