Sorption and Desorption of Ammonium from Liquid Swine Waste in Soils

Abstract

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)2SO4]. 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)2SO4 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)2SO4 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)2SO4 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.