GREEN MANURE - CORN ROTATION AND PHOSPHORUS ADSORPTION IN AN OXISOL

The objectives of this study were to quantify the P adsorption maximum in different green manure cropping systems and to evaluate the influe nce of the decomposition rate of green manure and some soil chemical p roperties upon such adsorption. It was studied the 0 to 20 cm layer of an Oxisol (Dark Red Latosol) under the following treatments: soil und er native cerrado, bare soil (five years) and the following green manu re cultivated in the dry season, after corn (cv. Pioneer 3072): Crotal aria juncea, Cajanus cajan, Mucuna aterrima and Brachiaria ruziziensis . The adsorption values were adjusted to Langmuir isoterm for determin ation of P adsorption maximum capacity (PAMC). The general trend of th e P maximum adsorption followed the order: discovered soil > Cajanus c ajan > Crotalaria juncea > Mucuna aterrima > Brachiaria ruziziensis > native cerrado. Soil organic matter amount and green manure decomposit ion rate had negative correlation with the P maximum adsorption, with correlation coefficients of 0.705 (P < 0.06) and 0.983 (P < 0.01), res pectively. The PAMC for the deepest layer was 56% higher than that of the superficial layer, suggesting the importance of organic matter on reducing P adsorption.