TITLE:
Land application of spent gypsum from ditch filters: phosphorus source or sink?
AUTHORS:
Karen L. Grubb, Joshua M McGrath, Chad J. Penn, Ray B. Bryant
KEYWORDS:
Phosphorus Sorbing Materials;
Gypsum, Ditch Filter
JOURNAL NAME:
Agricultural Sciences,
Vol.2 No.3,
August
8,
2011
ABSTRACT: Agricultural drainage ditches can provide a direct connection between fields and surface waters, and some have been shown to deliver high loads of phosphorus (P) to sensitive water bodies. A potential way to reduce nutrient loads in drainage ditches is to install filter structures containing P sorbing materials (PSMs) such as gypsum to remove P from ditch flow. The objective of this study was to determine the effect of land-application of gypsum removed from such filters on soil P forms and concentrations. Gypsum was saturated at two levels on a mass basis of P and applied to two soils of contrasting texture, a silt loam and a sandy loam and applied at both a high and low rate. The treated soils were incubated in the laboratory at 25oC, and samples were collected at 1, 7, and 119 days after initiation. Soil type, time after application, gypsum rate, and P saturation level all had a significant impact on soil P forms and concen-trations. However, it appears that land application of spent filter gypsum at realistic rates would have little effect on soluble P concentrations in amended soils.