With the purpose of evaluating the effectiveness of phosphogypsum and simple superphosphate in controlling ammonia losses by volatilization during the process of manure composting, an experiment was carried out in closed flasks of 1.6 liter, in which different rates (50, 100, 150 and 200 kg.t-1) of phosphogypsum and simple superphosphate were mixed with a substrate composed of equal amounts (on weight basis) of fresh chicken manure and cattle manure. Ammonia lost by volatilization was determined after 7, 14, 21, 28 and 35 days by trapping the gas in sulfuric acid solution placed in a small glass vial which, in turn, was maintained inside the volatilization flask The remaining acid after the exposure to ammonia was determined by titration with 0.025N NaOH. The amount of ammonia lost by volatilization from the samples decreased with the addition of both products, but for all rates applied, phosphogypsum was more efficient than simple superphosphate. The reduction in volatilization increased with the rate of application of both additives. There was an evidence that the reduction of ammonia loss was due to the presence of gypsum in the additives.
ammonia losses; phosphogypsum; simple superphosphate; manure composting
