Mineralização do carbono e do nitrogênio no solo e efeito na rúcula (Eruca sativa) de compostos obtidos por compostagem

Abstract

The automated composting has been recommended in Brazil as a promising strategy for the treatment of large volumes of liquid waste generated in pig farms, to mitigate the pollution potential of the same. But one of the composting problems are the loss of nitrogen (N) through the emission of gases such as ammonia (NH3) and nitrous oxide (N2O). Althoug the reduction of these losses can be achieved by adding substances to the pig slurry (PS) during composting, little is known about the effect of such additives in the compound decomposition rate in the soil and its capacity to supply the crops N. The aim of this study was to evaluate the effect of adding retorted oil shale (ROS) and nitrification inhibitor dicyandiamide (DCD) to PS during their automated composting on carbon (C) and N mineralization of compounds in two types of soil with contrasting texture (Ultisol and Oxisol) and its relation to the accumulation of N in the culture of arugula (Eruca sativa). The work was conducted at the Federal University of Santa Maria, Santa Maria, RS, in July 2015 to January 2016, consisting of an incubation experiment in the laboratory and the other in a greenhouse. The incubation experiment was conducted for 180 days under controlled temperature (25 °C) and humidity (80% of field capacity), in order to evaluate the mineralization of C and N in the soil. In each soil, they were evaluated the following treatments, with four replications and completely randomized design: T1- control without application of compost; T2- Compost with the application of only the PS at the substrate (mixture of wood shavings and sawdust) during composting; T3- Compost with added retorted oil shale (ROS) to PS during composting; T4- Compost with added ROS + DCD to PS during composting. In the greenhouse, we evaluated the effect of these same treatments of incubation on green mass (MG) production and dry (MD) and the accumulation of N in the culture of the arugula in two successive cuts, for 58 days of cultivation. The added amounts C and that was mineralized to 180 days in Latossolo ranged from 11.6 to 14.6% between the treatments T2, T3, T4, with no significant difference between them. In Ultisol mineralization index added C was significantly higher for the treatment T2 (21%) the average of the T3 and T4 (9.5%) which did not differ. The net N mineralization was observed only in treatment T2, with compost of DLS with additives (T3 and T4) showing occurrence of liquid N immobilization throughout the incubation period in both soils. The greater N mineralization rate for treatment T2 occurred in Argisol (19.4%) than in Latossol (10.8%). The addition of composts of DLS with (T2) and no additives (T2, T3, T4) provided an increase in the green and dry matter production and accumulation of nitrogen in the Arugula culture in both soils. In this way the use of the composts with and without additives is interesting for fertilization of cultures, it may increase in plant production, reduce environmental impacts and increase organic matter to the soil.