Phosphorus Removal From Agricultural Drainage Ditches Using Gypsum Filter Structures: Changes in Soil Phosphorus Forms Due to Application of Phosphorus Saturated Gypsum.

Agricultural drainage ditches can provide a direct connection between
agricultural fields and surface waters. Certain drainage ditches have
been shown to deliver high loads of phosphorus (P) to sensitive water
bodies. One potential way to reduce nutrient loads in agricultural
drainage ditches is to install filter structures containing P sorbing
materials (PSMs) such as gypsum to remove P directly from ditch flow.
One of the projected advantages of such a system would be the
potential application of PSMs to agricultural fields to provide
nutrients for crop production. The purpose of this study was to
evaluate in the laboratory the feasibility of such a strategy. Gypsum
was saturated at two levels on the mass basis of P, and applied to two
soil types, a silt loam and a sandy loam. The solution was applied at
both a high and low rate. The treated soils were incubated at 25° C
and samples were collected at 0, 1, 7, 28, 63, 91, 119, and 183 days
after saturation. Changes in chemically defined P forms in the soil
will be discussed.