Práticas para a redução das perdas de N na compostagem de esterco de galinha

Abstract

Chicken manure (CKM) encloses most N in the labile forms which are easily lost during composting if no additives are used to preserve N processed by decomposers and not incorporate in biodegradable C structures in the final compost. We aimed at evaluating the potential of different additives to reduce N gas forms and to enrich CKM-derived composts in N. Firstly, the effect of elemental S(0.25, 0.5, 1.0 and 2.0%), sugar cane bagasse (5, 10, 30 and 60%), eucalyptus sawdust (5, 10, 25 and 40%) and biochar rates (5, 10, 20 and 40%) in mixtures with EG were tested. The mixtures were incubated for 60 days. At the end of the incubation, compost mass, electrical conductivity (EC), pH and total N content in composts were evaluated. The elemental S at the 0.5% rate acidified and enriched the final compost with N in 50.7%. The use of C readily available from sugarcane bagasse in the incubated mixtures accelerates decomposition and allows, at the 40% rate, to retain more N in the final compost. Increasing of C/N ratio of residues under composting by the use of sugarcane bagasse accelerated composting and increased the N content in the humified compost. The use of S° can be combined with sugarcane bagasse as they provide conditions that minimize N losses during the incubation and produce more N-enriched ending compost. In sequence, N retention was evaluated through the use of NBPT, an inhibitor of urease, which, in optimum rate (0,5%) drastically reduced ammonia volatilization. Seven NBPT rates (0, 0.1, 0.25, 0.5, 1, 3 and 6%) were tested to find the optimum NBPT rate to retain more N in the final compost. Ammonia volatilization rates were quantified by trapping this gas in foams embedded with phosphoric acid and glycerin. Foams were collected at 0, 1, 2, 5, 8, 13, 20 and 30 days after the beginning of incubation. At the beginning and at the end of the experiment, the total N, nitrate-N and ammonium-N contents, pH, EC and the compost remaining mass were determined. The NBPT rates of 0, 0.1, 0.25, 0.5 and 1% showed a continuous growth of NH3 volatilization up to the end of the incubation, however, NBPT at the rates of 3 and 6% drastically ceased NH3 volatilization. All treatments presented lower rates of volatilization when compared to the control (EG only). At the rates of 0, 0.1, 0.25 and 0.5% NBPT, the pH values increased at the end of the incubation, as well as the N-nitrate contents. On contrary, the ammonium contents and the remaining mass were smaller. In relation to the 1, 3 and 6% NBPT rates, a reduction in pH and nitrate-N contents were observed, as well as a small loss of mass at the end of incubation. Thus, the rate of 0.5% NBPT could be recommended to reduce N losses by 20% (in relation to the control), allowing increasing retention of N in the final matured and stabilized compost. It is necessary to test the effect of NBPT on N processes in field composting conditions, considering that this study was carried out in laboratory through a controlled incubation experiment.