Rev. Bras. Ciênc. Solo.1997;21(4):643-50.
Preferential forms of phosphorus accumulation in soils cultivated with sugar-cane in northeastern Brazil
01/Dec/1997
DOI: 10.1590/S0100-06831997000400015
The objective of this work was to quantify the main forms of P derived from fertilizer in soils of varying physical and chemical properties, cultivated with sugar-cane, in Pernambuco. Soils from 11 commercial plantations were sampled following the harvest of the plant-cane (Jan. 1994), that had been fertilized in the furrow 18 months before. To find samples with fertilizer-derived P, a pit was opened perpendicular to the plant line and 28 soil samples were taken with the aid of a metal grid measuring 70 cm long by 40 cm high, with 10×10 cm cells. The grid was fixed 10 cm below the soil surface and centered on the residues of the seedpieces. Phosphorus in all these samples was extracted with 0.1 mol L-1 NaOH. In all cases the largest P concentrations were found in the 10-20 cm layer. Two samples were then selected from this layer for additional work, those with the highest and lowest NaOH extractable-P content, for each soil. Phosphorus in these selected samples was sequentially extracted with resin (P-res), NaHCO3 (inorganic and organic P-bic), NaOH (inorganic and organic P-OH), H2SO4 (P-ac.), and followed by a final digestion with H2SO4 and H2O2 (P-rdu). Most of the difference between samples with high and low P contents (DP), attributed to the fertilization 18 months before, was found in inorganic (P-res, Pi-bic, Pi-OH and P-ac)) forms. In five of the soils, fine textured and with high dithionite-extractable Fe and Al, more than 50% of DP was found as Pi-OH. In the other six soils, P was similarly distributed among P-res, P-bic and P-OH or even favored the resin and bicarbonate-extractable forms (more sandy soils). The presence of large amounts of labile P-res and P-bic forms, even after 18 months of soil-fertilizer contact, suggests the possibility of obtaining residual fertilizer effects in some of these soils.
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