Water Soluble P From Poultry Litter and Flue Gas Desulfurization Gypsum Amended Hay Field in Watkinsville GA.

The research focused on evaluating if flue gas desulfurization (FGD) gypsum reduces P losses from hayed or pasture fields receiving poultry litter (PL).  Plots were established in fall of 2008 on a field that had been hayed for at least 20 years. Treatments included four rates of FGD gypsum  (0, 2.2, 4.5, and 9.0 Mg ha^-1) each with PL at 13.5 Mg ha^-1, and two control treatments,  one with no FGD gypsum or PL (0-0), and the other with FGD gypsum at the highest rate without PL ( 0-9.0). The six treatments were replicated three times. The 4 by 6 m plots received treatments in April to early May in 2009, 20010 and 2011. Soil samples were collected from 0-2.5, 2.5-5.0, 5.0-7.5, 7.5-15.0 cm depth just before rainfall simulation runs beginning 6/8/2009 and 5/9/2011 and analyzed for water soluble P (WSP). The surface 0- to 2.5-cm soil depth contained a large part of the WSP measured in sections down to 15 cm (Least square means 4 to 79 mg kg^-1). Treatment effects occurred in the surface 5-cm depth only. In the 0- to 2.5-cm depth, PL doubled the WSP in both years compared with the (0-0) treatment (p ≤ 0.002). Addition of gypsum to the PL resulted in a significant linear decrease of WSP with increasing gypsum rate (p = 0.003) in 2009 but not in 2011.  Gypsum at the highest rate with litter reduced WSP by ~26% compared with the treatment with litter only. Addition of gypsum to the zero amendment control reduced WSP by 38% (p = 0.05). The only treatment effect in the 2.5- to 5.0-cm depth was a 1.7- to 2.4-fold increase in WSP due to litter or litter with gypsum in 2011 compared with the (0-0) control (0.003 < p ≤ 0.084).