Sorption and desorption of ammonium from liquid swine waste in soils

Understanding the sorption and desorption behavior of NH4+ in soils associated with animal waste is important because of the potential for the formation of NO3- and subsequent leaching that affects ground water quality. Batch equilibration experiments were conducted to evaluate the sorption and desorption of NH4+ in two soils exposed to a complex matrix (liquid swine waste) and a simple matrix [aqueous solution of 0.01 M CaCl2 containing (NH4)(2)SO4]. Kennebec silt loam (fine-silty, mixed, mesic Cumulic Hapludolls) and Haynie very fine sandy loam (coarse-silty, mixed, calcareous, mesic Mollic Udifluvents) were used. This study revealed that the sorption and desorption behavior of NH4+ in soils exposed to (NH4)(2)SO4 Solutions with a 0.01 M CaCl2 matrix is significantly different from that in soils exposed to liquid swine waste. Faster sorption rate, lower sorption capacity, and higher desorption capability were observed for NH4+ in soils exposed to the (NH4)(2)SO4 Solution compared with soils exposed to the liquid swine waste. Sequential extraction could not extract nonexchangeable NH4+ in both soils exposed to liquid swine waste, while a significant amount of nonexchangeable NH4+ was extracted from the two soils that were initially exposed to the (NH4)(2)SO4 solutions. The high dissolved organic C (DOC) content coupled with the high pH in swine waste appears to stimulate the sorption and retard desorption of NH4+ in the two soils. This study revealed that batch equilibrium studies using solutions with simple matrixes may underestimate the sorption or overestimate desorption of NH4+ in soils associated with swine waste.