Can Surface-Applied Zeolite Reduce Ammonia Losses from Beef Cattle Feedyard Manure? a Laboratory Study.

Ammonia (NH₃) emission from beef cattle feedyard manure results in losses of nitrogen (N), which may negatively affect environmental quality. The magnitude and rate of NH₃ volatilization from feedyards partially depends on the amount of urinary urea excreted and ionization of ammonium (NH₄⁺) into NH₃ following urea hydrolysis. Zeolite clinoptilolite is a naturally occurring, porous aluminosilicate mineral that can sorb and sequester cations within its negatively charged framework structure. Zeolite has been used to mitigate NH₃ losses and improve fertilizer value of compost and manure in livestock barns. Zeolite application to pen surfaces could be a practical and cost-effective means of reducing NH₃ losses; however, few studies have evaluated its efficacy on open-lot beef cattle feedyards. Objectives of this study were to (1) characterize NH₄⁺ sorption by zeolites with differing physicochemical properties and (2) evaluate zeolite effects on rates and cumulative losses of NH₃ following urine application to feedyard manure. Batch incubation studies with four commercially available zeolites revealed that NH₄⁺ sorption by zeolite was rapid (1 to 2 h) with large differences in sorption potential largely related to zeolite pH. Maximum sorption ranged from 28 to 97 cmol NH₄⁺-N kg^-1 zeolite. Effects of zeolite application rate [0.5% to 10.0% of manure dry matter (DM)] on sorption and desorption characteristics in a manure/urine matrix were highly variable but tended to be proportional to zeolite application rate: as little as 0.5% zeolite increased NH₄⁺-N recovery up to 19%. In flow-through chamber studies, higher rates of zeolite did not reduce cumulative NH₃ emissions, as 1.0% zeolite reduced cumulative NH₃ emission by 42% and 5.0% zeolite reduced N losses by only 18% compared to unamended manure. Surface application of zeolite has potential for mitigating feedyard NH₃ losses, but specific zeolite properties influenced its effectiveness.