Forms of soil phosphate and their availability to plants

Abstract

The P fractions in 24 soils of the Llanos Altos Occidentales and their relationship with 'available' P measured by plant uptake in the glasshouse, was determined. Seven of the soils showed high levels of P available to plants, five moderate levels and 12 deficient levels. Ca-P was predominant in nine of the soils and Fe-P and/or Al-P in ten soils. From glasshouse studies and multiple regression analysis it was concluded that the most important fraction supplying P to plants is P soluble in NH4Cl. Fe-P may provide a slow supply of 'available' P.