| Summary: | Loss of N via NH₃ 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 NH₃ volatilization during aerobic composting of poultry layer manure, examine the
potential of natural zeolites to adsorb the volatilized NH₃ 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 NH₄⁺ adsorption capacity. The effectiveness of a
clinoptilolite zeolite ZI as an NH₄⁺
adsorbent at pH range 4 to 7 was tested. The kinetics of NH₄⁺
exchange on the zeolite was evaluated at the pH range 4 to 7, initial NH₄⁺
concentrations ranging from
70.1 to 1401 mgN L⁻¹, and a temperature range of 25 to 55 °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 NH₄⁺
and N0₃⁻ 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 NH₄⁺. The amount of NH₄
⁺ adsorbed increased with increasing
pH and NH₄⁺ concentration. The estimated NH₄⁺
adsorption capacity increased linearly with pH (r2 =
0.994), ranging from 9660 mg N L⁻¹ at pH 4 to 13830 mg N L⁻¹ at pH 7. Studies on thermodynamics of
NH₄⁺exchange on the zeolite ZI indicated a higher activation energy for desorption (5.65 kJ mol1) than
for adsorption (2.32 kJ mol⁻¹). Composting poultry manure with 60% zeolite ZI (weight basis) reduced
NH₃ losses by 44.3%. The compost had total N concentration of 17.04 g N kg⁻¹ and a high NH₄
⁺ concentration (52.8% of the total N). The 60% zeolite Zl-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. === Land and Food Systems, Faculty of === Graduate
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