In tropical oxidic soils, organic phosphorus (Po) plays an important role in plant nutrition. In addition, Po cycling in clay soils is very complex due to the greater participation and influences of active clay fractions on nutrient availability. The objective of this study was to evaluate the effects of converting a native forest to a secondary forest or Brachiaria brizantha pasture on the Po contents of clayey Oxisols in the eastern region of Amazonia, Itupiranga, in the State of Pará. Soil samples were collected from areas of native forest (NF), secondary forest of 8-10 years (SF), and pastures of 1-2 years (P1-2), 5-7 years (P5-7) and 10-12 years (P10-12) in 3 replicates for each land-use type and depth sequential P fractionation was conducted to obtain the following 3 fractions: sodium bicarbonate-, acid- and alkali-soluble. The samples obtained from the different land use types indicated different P accumulation abilities, suggesting that slash-and-burn clearing of a forest increased the soil P contents. On average, the total organic phosphorus (Pot) content corresponded to 21% of the total soil phosphorus (Pt), with a predominance of the moderately labile fraction (Po- H+), followed by the labile form (Pol) and the moderately resistant fraction (Po-OH-), with average Pot contents of 65%, 21% and 15%, respectively. Over a short-term period, the P availability represented by Pol was higher in the soils from the native forest and secondary forests. In addition, the available P over a medium-term period, as represented by Po-H+, indicated a higher P content in the pasture soil.
Online ISSN: 1459-0263Year: 2015, Vol. 13, Issue 2, pages 274-282.Publisher: WFL.
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