EFFECT OF GRAZING PIGS ON CARBON, NITROGEN AND PHOSPHORUS FRACTIONS IN SOIL

The objective of this study was to evaluate the influence of grazing pigs on some soil chemical variables in a Mollisol in Maracay - Venezuela, under isohyperthermic conditions. Soil samples were taken from grazed (6 kg/m(2)) and non-grazed plots. Tat (0-5 or 5-10 cm depth), using a 2x2 factorial design. Total nitrogen, ammonia nitrogen, nitrate nitrogen and organic nitrogen were assessed. The extraction and fractionation of soil organic matter (SOM) and total oxidable organic carbon, total extractable carbon (CET), the carbon bonded to humic acids (CAH), fulvic acids (CAF), and non-humic substances (CSNH) were determinated. In addition, the phosphorous in the soil was fractionated by using the method of Medley; extracting the fractions: resin exchangeable phosphorus (P-membrane), phosphorus extracted with sodium bicarbonate, NaOH extractable inorganic phosphorus, inorganic phosphorus and inorganic phosphorus extractable by HCl and inorganic phosphorus extractable in hot HCl. The treatments did not affect nitrogen, CAH and CAF, but the CET and CSNH were affected. An increase on the fractions of phosphorus was observed, with higher increases in exchangeable phosphorus in grazed plots.