EFFECT OF NITROGEN APPLICATION IN THE MICROBIAL ACTIVITY IN THE STRAW DECOMPOSITION OF SORGUM IN NO TILL IN "CERRADO" SOIL

Abstract

The microbial activity of the ground participates of diverse important processes in the ground, as the decomposition of plant and animal residues and the cycle of nutrients. Residues with high relation C/N suffer to slower decomposition, what it can immobilization of certain nutrients, mainly N. The objective from this study were to evaluate the effect of the nitrogen application in the microbial activity of the ground and in the straw decomposition of sorgum in ground of closed under no till. The study was composed of 2x6 factorial, being nitrogen applied at two levels (with N, at 30 kg ha-1, and without N), and six times (0;15; 30; 45; 60 and 75 days after application the N), in the experimental area of Federal University of Goiás State at Jataí-GO. The carbon of the microbial biomass (C-BM), microbial respiration of the soil (Resp), organic carbon (C-org), quocient metabolic (qCO2), supply carbon (Est-C), rate of decomposition and half life of the straw of sorgum had been determined. The application of 30 kg ha-1 of N did not influence the Resp, C-org and qCO2, however, for C-BM the application of N provoked decrease in 20% in relation to the treatment without N. With exception of C-org, all the others had varied during the period of study. The decomposition tax was bigger in the treatments with N, that presented 21% increase. It is concluded that the application of N at 30 kg ha-1 does not affect the microbial activity, however increases the rate of decomposition of the straw of sorgum.

KEY-WORDS: Microbial biomass; rate of decomposition; qCO2; microbial respiration.