THE EFFECT OF SOURCES AND APPLICATION DOSES OF NITROGEN ON THE CHEMICAL PROPERTIES OF AN OXISOL CULTIVATED WITH GUINEA GRASS

Nitrogen supplementation has been an important means for increasing yield in tropical gramineous forage plants in Brazil because, in most growing areas, the levels of this nutrient in the soil do not adequately meet crop needs. We assessed the effect of different sources and application rates of N on the chemical properties of an Oxisol (Latossolo Amarelo) and the production of Panicum maximum cv. Mombaca. The experiment was carried out at the Instituto Federal do Espirito Santo (State of Espirito Santo, Brazil), Santa Teresa campus. A randomized block experimental design with three replications was used in a 3 x 6 factorial arrangement, with three N fertilizers (urea, ammonium sulfate, and calcium nitrate) and six N doses (0, 120, 240, 360, 480, and 600 kg ha(-1)), for a total of 54 experimental units. The N was applied every 28 days, always after cutting the forage, for a total of seven applications over the 196-day experimental period. At the end of the experiment, soil samples were collected at the depth of 0-20 and 20-40 cm with the aid of a Dutch auger to evaluate the effect of the application rate on the chemical properties of the soil at the different depths. The experimental results showed high potential for soil acidification from ammonium sulfate. The changes brought about in soil pH resulted in changes in exchangeable Al content, in potential acidity, and in P availability in the soil. The application of high rates of N in the form of ammonium sulfate and calcium nitrate led to leaching of bases, especially K at the depth of 20-40 cm.