Effect of adding alum or zeolite to dairy slurry on ammonia volatilizationand chemical composition

Development of cost-effective amendments for treating dairy slurry has beco me a critical problem as the number of cows on farms continues to grow and the acreage available for manure spreading continues to shrink. To determin e effectiveness and optimal rates of addition of either alum or zeolite to dairy slurry, we measured ammonia emissions and resulting chemical changes in the slurry in response to the addition of amendments at 0.4, 1.0, 2.5, a nd 6.25% by weight. Ammonia volatilization over 96 h was measured with six small wind tunnels with gas scrubbing bottles at the inlets and outlets. Ma nure samples from the start and end of trials were analyzed for total nitro gen and phosphorus, and were extracted with 0.01 M CaCl2, 1.0 M KCI, and wa ter with the extracts analyzed for ammonium nitrogen, phosphorous, aluminum , and pH. The addition of 6.25% zeolite or 2.5% alum to dairy slurry reduce d ammonia emissions by nearly 50 and 60%, respectively. Alum treatment reta ined ammonia by reducing the slurry pH to 5 or less. In contrast, zeolite, being a cation exchange medium, adsorbed ammonium and reduced dissolved amm onia gas. In addition, alum essentially eliminated soluble phosphorous. Zeo lite also reduced soluble phosphorous by over half, but the mechanism for t his reduction is unclear. Alum must be carefully added to slurry to avoid e ffervescence and excess additions, which can increase soluble aluminum in t he slurry. The use of alum or zeolites as on-farm amendment to dairy slurry offers the potential for reducing ammonia emissions and soluble phosphorus in dairy slurry.