CAN SURFACE-APPLIED ZEOLITE REDUCE AMMONIA LOSSES FROM FEEDYARD MANURE? A LABORATORY STUDY

Ammonia (NH3) emission from beef cattle feedyard manure results in losses of nitrogen (N), which may negatively affect air, soil, and water quality. The magnitude and rate of NH3 volatilization from feedyards partially depends on the amount of urinary urea excreted and dissociation 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, sewage sludge, and manure in livestock barns; however, few studies have evaluated its efficacy on open-lot beef cattle feedyards. Zeolite application to pen surfaces could be a practical and cost-effective means of reducing NH3 losses. 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 application of artificial urine 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/artificial urine matrix were highly variable but tended to be proportional to zeolite application rate: as little as 0.5% zeolite increased NH4+-N recovery by 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. Further studies are warranted to evaluate effects of repeated zeolite application, co-application of zeolite and urease inhibitors, and cost: benefit ratios of zeolite application at commercial feedyards.