Characterization of Ammonium Sorption by Beef Cattle Feedyard Manure

Abstract

Ammonia (NH3) emissions from beef cattle feedyards represent a loss of agronomically important N and can potentially affect the environment. Sorption of ammonium (NH4+) and NH3 by mineral and organic solids decreases the proportion of free, aqueous ammoniacal N, which reduces volatilization potential. In the U.S., the High Plains region of Texas is subject to arid conditions with widely fluctuating temperatures. Furthermore, feedyard manure contains little soil and has high dry matter (DM) content; therefore, it is unclear if sorption parameters determined for soils or liquid manure systems are valid for feedyards. Our objectives were to use batch equilibration experiments to characterize NH4+ sorption by two feedyard manures. Kinetic and isotherm studies with (NH4)2SO4/0.01 M CaCl2 solutions revealed that feedyard manures could sorb up to 227 cmol kg-1 NH4+-N and that sorption was rapid and linearly related to NH4+ concentration. The Freundlich partitioning coefficient (Kp) for NH4+ sorption averaged 13.3 L kg-1. From 58% to 96% of the sorbed NH4+ was readily desorbable with 0.01 M CaCl2, and up to 81% was volatilized as NH3 when manures were air-dried. Temperature influenced sorption, with 112% more NH4+ sorption at 4C than at 22C. These results indicate that NH4+ sorption by manure on feedyard surfaces may temporarily reduce NH3 volatilization, particularly during winter.