Phosphorus fractions in a Luvissolo Crómico Órtico soil under agroforestry systems in the Sobral county, Ceará, Brazil
Abstract
The objective of this study was to evaluate the soil phosphorus (P) fractions in Agroforestry and conventional systems in order to verify the hypothesis that the analyzed fractions are modified by the soil management of the soil. Soil samples were collected, in September of 2002, in the depths of 0-6; 6-12; 12-20 and 20-40 cm, from an experiment installed since 1997, in the Crioula Farm, of the CNPC-EMBRAPA, Sobral, Ceará, Brazil. It were selected the following systems: Agrosilvopastoral (AGP), Silvopastoral (SILV), Traditional cultivated in 1998 (TR-98), Cultivated intensive (CI), Natural forest 1 (MN-1) and Natural forest 2 (MN-2). The phosphorus fractions were fractionated as described by Bowman (1989). The experimental design was randomized complete blocks in a split plot scheme with five replications. The treatments had been arranged in subdivided parcels, being the definite systems of culture as the parcel and the four depths as subplots. The agrosilvopastoral presented the higher concentration of total phosphorus. The Agrosilvopastoral and Silvopastoral systems presented the best distributions in the inorganic and organic P fractions when compared with natural forest areas. In relation to the TR-98 and CI systems it was observed an elevated percentage of the Pi (H+) fraction and reduced of the participation fraction Po (H+). Results suggest that the organic soil P reservoir tends to be depleted with the continuity of this use. In the other hand it was verified that the agroforestry systems favor increases in the organic P fraction speks, conditioning the higher P cycling in the soil.
