Reducing nitrogen losses during composting of poultry manure using the natural zeolite clinoptilolite

Loss of N via NH{dollar}sb3{dollar} volatilization during composting of poultry manure reduces the agronomic value of the end-product and contributes to environmental pollution. The objectives of this study were to evaluate N losses via NH{dollar}sb3{dollar} volatilization during aerobic composting of poultry layer manure, examine the potential of natural zeolites to adsorb the volatilized NH{dollar}sb3{dollar} during composting, and evaluate the poultry manure-zeolite compost as a controlled-release N fertilizer. Eleven mineral samples were characterized for their physical properties, chemical composition, and NH{dollar}sb4sp+{dollar} adsorption capacity. The effectiveness of a clinoptilolite zeolite Z1 as an NH{dollar}sb4sp+{dollar} adsorbent at pH range 4 to 7 was tested. The kinetics of NH{dollar}sb4sp+{dollar} exchange on the zeolite was evaluated at the pH range 4 to 7, initial NH{dollar}sb4sp+{dollar} concentrations ranging from 70.1 to 1401 mg N L{dollar}sp{lcub}-1{rcub},{dollar} and a temperature range of 25 to 55{dollar}spcirc{dollar}C. Ammonia emissions were measured during composting of poultry manure with zeolites and other amendments in a laboratory composting simulator. The resulting composts were applied to a sand based medium planted with ryegrass (Lolium multiflorum) where growth, N uptake, and NH{dollar}sb4sp+{dollar} and NO{dollar}sb3sp-{dollar} leaching were evaluated. The cation exchange capacity (CEC) and purity of the zeolites, with respect to mineralogy and constituent ions, influenced their affinity and adsorptive capacity for NH{dollar}sb4sp+.{dollar} The amount of NH{dollar}sb4sp+{dollar} adsorbed increased with increasing pH and NH{dollar}sb4sp+{dollar} concentration. The estimated NH{dollar}sb4sp+{dollar} adsorption capacity increased linearly with pH (r{dollar}sp2{dollar} = 0.994), ranging from 9660 mg N L{dollar}sp{lcub}-1{rcub}{dollar} at pH 4 to 13830 mg N L{dollar}sp{lcub}-1{rcub}{dollar} at pH 7. Studies on thermodynamics of NH{dollar}sb4sp+{dollar} exchange on the zeolite Z1 indicated a higher activation energy for desorption (5.65 kJ mol{dollar}sp{lcub}-1{rcub}){dollar} than for adsorption (2.32 kJ mol{dollar}sp{lcub}-1{rcub}).{dollar} Composting poultry manure with 60% zeolite Z1 (weight basis) reduced NH{dollar}sb3{dollar} losses by 44.3%. The compost had total N concentration of 17.04 g N kg{dollar}sp{lcub}-1{rcub}{dollar} and a high NH{dollar}sb4sp+{dollar} concentration (52.8% of the total N). The 60% zeolite Z1-amended compost treatment produced the highest ryegrass dry matter, N accumulation and N use efficiency compared to the other composts evaluated. Nitrogen leaching losses were low. Although composting poultry manure amended with the natural zeolite clinoptilolite can reduce N losses to the atmosphere, recycling it for crop utilization, the cost of the high amount of zeolite required may be prohibitive.