Bactérias amonificantes e nitrificantes e teores de amônio e nitrato afetados por plantas de cobertura e fertilizantes nitrogenados

Abstract

The aim was to evaluate the effect of cover crops and N sources on ammonifying and nitrifying bacteria activities, as well as the levels of nitrate and ammonium in the soil. The experiment was conducted in an oxisol on no-tillage system (NTS) for six years. The experimental design was randomized blocks, arranged in a split plot scheme with four replications. The plots consisted of six species of cover crops (Brachiaria brizantha, Brachiaria decumbens, Brachiaria humidicola, Brachiaria ruziziensis, Pennisetum americanum and Crotalaria spectabilis) and the split plots by control treatment and three nitrogen sources (1 – control, no nitrogen fertilization, 2 - calcium nitrate, 3 - ammonium sulfate and 4 – ammonium sulfate + dicyandiamide (DCD) fertilized immediately after rice emergence in the dose of 40 kg ha-1 of N. It was evaluated the activity of bacteria and the nitrate and ammonium in the soil at 15 DAE. The cover crops millet (Pennisetum americanum), crotalaria (Crotalaria spectabilis), Brachiaria brizantha, B. decumbens and B. humidicula provided the highest level of ammonium in the soil; The use of nitrification inhibitor (dicyandiamide-DCD) inhibited part of the nitrifying bacteria and provided the highest levels of ammonium in the soil. The activity of nitrifying and ammonifying bacteria was higher in plots cultivated with Brachiarias. Cover crops with the use of DCD could be used as one strategy to increase the level of ammonium in the soil under NTS.