Ammonia volatilization in soil treated with tannery sludge

The utilization of tannery sludge in agricultural areas can be an alternative for its disposal and recycling. Despite this procedure may cause the loss of nitrogen by ammonia volatilization, there is no information about this process in tropical soils. For two years a field experiment was carried out in Rolândia (Paraná State, Brazil), to evaluate the amount of NH3 volatilization due to tannery sludge application on agricultural soil. The doses of total N applied varied from zero to 1200 kg ha−1, maintained at the surface for 89 days, as usual in this region. The alkalinity of the tannery sludge used was equivalent to between 262 and 361 g CaCO3 per kg. Michaelis-Menten equation was adequate to estimate NH3-N volatilization kinetics. The relation between total nitrogen applied as tannery sludge and the potentially volatilized NH3-N, calculated by the chemical-kinetics equation resulted in an average determination coefficient of 0.87 (P > 0.01). In this period, the amount of volatilized NH3 was more intense during the first 30 days; the time to reach half of the maximum NH3 volatilization (Km) was 13 an 9 days for the first and second experiments, respectively. The total loss as ammonia in the whole period corresponded in average to 17.5% of the total N applied and to 35% of the NH4+-N present in the sludge. If tannery sludge is to be surface applied to supply N for crops, the amounts lost as NH3 must be taken into consideration.