HP-HG exhibits higher P concentrations in all fractions

1. LP = 25% saturation HP = 75% saturation LG = 5.6 Mg gypsum ha-1 HG = 22.4 Mg gypsum ha-1 P and Ca application rate Lab for Ag and Environmental Studies Department of Environmental Science and Technology (kg-P ha-1) (kg-Ca ha-1) LP-LG 35 1232 HP-LG 105 1232 LP-HG 140 4928 HP-HG 420 4928 Methods: Soil Phosphorus Fractionation P Pool Extracted • Labile P • Easily extractable, most available to plants and algae, P in solution • Plant available P – loosely held Fe/Al and organic P • Fe- and Al-Bound P and associated with humic compounds • Strongly held P – phytate P, mineral P, held in internal structures Changes in Soil Phosphorus Forms Due to Application of Phosphorus Saturated Gypsum Karen L. Grubb1, Joshua M. McGrath1, Chad J. Penn2, Ray B. Bryant3 Results Introduction Accelerated eutrophication of the Chesapeake Bay has become a large concern over the past few decades. Direct removal of phosphorus from surface water using by-product materials that have the capacity to sorb phosphorus (known as Phosphorus Sorbing Materials- PSMs) have potential as BMPs in agricultural drainage ditches. Gypsum filters designed to remove phosphorus (P) from agricultural drainage are currently being evaluated in Maryland (USA). A laboratory incubation study was performed to determine how land-application of the P saturated gypsum would affect soil P forms and availability and to evaluate the effectiveness of P saturated gypsum as a fertilizer material. Spent ditch filter gypsum was simulated by saturating FGD gypsum to two levels on a mass basis of P, and applied to two soil types, a silt loam and a sandy loam at both a high and low rate. The treated soils were incubated at 25° C and samples were collected 0, 1, 7, 28, 63, 91, 119, and 183 days after amendment. Changes in chemically defined P forms in the soil are presented. Treatment Combinations • Cannot show main effect of soil for H2O and NaOH due to interactions • Due to higher buffer capacity, silt loam has higher extractable P in all fractions except water • NaOH included for comparisons, day involved in 3-way interaction soil*gyprate*psat • P shift from more labile P (H2O) to more insoluble forms over time • Objective • Determine effect of land application of spent gypsum from ditch filters on soil P forms. • Experimental Design • Treatment Factors • Gypsum- 2 Levels (mass basis of P) • Low Rate of Gyp (5.6 Mg gypsum ha-1) • High Rate of Gyp (22.4 Mg gypsum ha-1) • P Saturation- 2 Levels (based upon P isotherms) • 25% saturation (6.25 mg P g gyp-1) • 75% saturation (18.75 mg P g gyp-1) • Soil Type- 2 Levels • Sandy Loam- Galestown Sandy Loam • Silt Loam- Mattapex Silt Loam • Time- 3 Levels • Day 1 • Day 7 • Day 119 • 2 x 2 x 2 x 3 factorial structure • The factorial combinations applied to experimental units as randomized complete block design (RCBD) in 4 blocks (incubators) • HP-HG exhibits higher P concentrations in all fractions • NaHCO3 pool exhibits slightly different trends, with LP-HG having significantly higher P concentrations than LP-LG • Conclusions to Date • HP-HG tends to have more extractable P in all pools in sequential extraction • At agronomic acceptable Ca rates, P saturation levels did not significantly alter soil test P concentrations • P trapped by PSMs can be returned to the land in a potentially less mobile form but may also be plant available 1- University of Maryland Department of Env. Science and Technology 2- Oklahoma State University Department of Plant and Soil Sciences 3- USDA-ARS Pasture Systems and Watershed Research Laboratory