PHOSPHORUS FORMS ON SOILS OF PANAMA

Abstract

The objective was to determine forms of phosphorus (P) in soils from the four most common taxonomic orders in Panama. From 34 unfertilized soils, developed from different parent material, samples of 0-20 cm depth were analyzed. The inorganic-P (P-FeAl, P-CO₃, P-Occluded and P-Ca) was fractionated according to Olsen and Sommers methodology and organic P (Porg-labile, Porg-moderately-labile and Porg-moderately-resistant) according Hedley. The determination was carried out at the IDIAP Soil Laboratory in Divisa, Herrera province from January to December 1998. A completely randomized experimental design with four replicates was used. Total P was obtained as a result of the sum of the various fractions and their content ranged from 165 mg kg^-1 to 764 mg kg^-1. Soils developed from sediments and with fine granulometry presented higher total P content. The P-FeAl inorganic fractions predominated in all soils, mainly in those with high Al saturation. The P-Ca fraction was lower in most soils, except for some alfisols and inceptisols. Organic- P values between 14 mg kg^-1 and 182 mg kg^-1 were found, however, in highly weathered soils the Porg-labile fraction predominated over the others. There was a positive and significant correlation at 0,05 probability between the fraction of total P and clay content (0,86); Organic carbon and total organic- P (0,72) and Saturation of Al and P-FeAl (0,94). Knowing the P fractions in the soils of Panama contributes to improve its management.