Cotton Yield and Soil Water As Affected by Annual Applications of FGD Gypsum.

Flue Gas Desulfurized (FGD) gypsum is a by-product of energy production from burning coal.  This material is currently being land filled but offers an opportunity as a soil amendment in agricultural practices.  From 2009 through 2011, FGD Gypsum was applied annually on a cotton field across both no-till and tilled systems at rates of 0, 2.24, 4.48, 6.72, and 11.2 Mg ha^-1 to determine if gypsum rate affected cotton yield.  In 2009, neither tillage nor gypsum rate significantly affect yield.  However, in 2010 both tillage and gypsum rate significantly affect yield, with greater yields in the no-till system and 0 Mg gypsum ha^-1 with an irregular yield decline across other gypsum rates.  In 2011, there were no significant differences in yield from tillage or gypsum rate.  Yields across years were not significantly different amongst tillage systems, but yield was significantly affected by gypsum rate with a decreased yield from the addition of any rate of gypsum.  In 2010 and 2011, soil water content in the 0, 2.24, and 4.48 Mg gypsum ha^-1 was monitored using time domain reflectrometry (TDR) at 15, 30, and 45 cm.  There were no significant differences in water content across tillage systems or gypsum rates in 2010.  An irregular distribution of significance of soil moisture content due to tillage was observed during the 2011 growing season.  Nearing the end of the growing season in 2011, significantly higher soil moisture content was observed with applied gypsum compared to the control.  Our results indicate under certain conditions, annual gypsum applications can decrease cotton yield.