Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2012
Publication Date: 9/25/2012
Citation: Waldrip, H., Todd, R.W., Cole, N.A. 2012. Characterization of ammonium sorption by beef feedyard manure. Transactions of the ASABE. 55(4):1609-1619.
Interpretive Summary: When ammonia gas escapes from beef cattle feedyards, a valuable plant nutrient is lost, air and water quality is reduced, land can be acidified, and there could be negative effects on animal and human health. Models are mathematical tools that predict ammonia loss, but we do not know how well current models estimate ammonia emissions from beef cattle feedyards. One important part of these models is how strongly the ammonium ion is held, or sorbed, by manure. If it is held strongly, then there is less chance of losing ammonia as gas. We determined how much ammonium that beef cattle manure could sorb, and how easily the sorbed ammonium could be removed. Then, we used basic chemistry concepts to characterize binding by beef cattle manure. We found that most ammonium sorbed after just one day, and anywhere from half to almost all of the sorbed material was easily removed. When we added more ammonium there was higher sorption. Finally, we dried manure for three days and saw that most of the sorbed ammonium was lost as ammonia gas. This shows that binding of ammonium by manure might slow ammonia loss, but this may not be important in overall control of ammonia emission from beef cattle feedyards.
Technical Abstract: Ammonia (NH3) emissions from beef cattle feedyards represent a loss of agronomically important nitrogen (N), and can potentially affect the environment. Process-based models have been developed to estimate NH3 flux from various types of livestock operations; however, their applicability to feedyards is unknown. Ammonia emission is dependent on the proportion of free, aqueous NH3, and dissociation of NH4**+ into NH3 and H**+. Sorption of NH4+** and NH3 by solids decreases soluble ammoniacal N, lowering volatilization potential. The Southern High Plains are subject to arid conditions with widely fluctuating temperatures, and feedyard manure is fibrous, contains little soil, and has a high dry matter (DM) content; therefore, it is not clear if model parameters determined for soils or liquid manure systems are valid for feedyards. Our objectives were to use batch equilibration experiments to characterize sorption of NH4**+ by feedyard manure. In kinetic sorption studies with 3.6 cmol/L NH4**+-N, equilibrium was reached within 24 h, with sorption of 20.7 cmol/kg NH4**+-N. Desorption studies revealed that 58 to 96% of the sorbed NH4**+-N was exchangeable with 0.01 M CaCl2, and manures differed in binding strength. Increasing NH4**+ concentration from 0.7 to 36 cmol/L NH4**+-N resulted in a linear (C-type) increase in sorption, with a maximum of 227 cmol/kg NH4+**-N. After 3 d of air-drying, up to 81% of sorbed NH4**+-N was volatilized. These results indicate that while association with manure may temporarily reduce NH4**+ dissociation, sorption may not be an important long-term mechanism controlling feedyard NH3 emissions.