KINETICS OF PHOSPHATE RELEASE IN SOME FOREST AND SAVANNA SOILS
KINETICS OF PHOSPHATE RELEASE IN SOME FOREST AND SAVANNA SOILS
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Date
2006-07
Authors
ABDU, NAFIU
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Abstract
The rate at which phosphate (P) is desorbed from the soil surface into soil solution
is a key factor that regulates the continuous supply of P to crops. Understanding the
kinetics of P desorption is paramount for effective P management in order to boost
agricultural production and to minimize environmental degradation and pollution. The
objectives of this study were to compare several kinetic models for describing P
desorption rates in savanna soils of varying lithogenic origins, and to determine the effect
of soil properties on P release rate. Phosphate desorption patterns were measured from
soils derived from three different parent materials using anion exchange resin. The
desorption patterns included an initial fast reaction that lasted for about 500 mins,
followed by a slow release that continued up to 1200 mins. Phosphorus desorption rates by
anion exchange resins were best described by three empirical kinetic models: Elovich
equation, the parabolic diffusion equation and the fractional power equation in that order.
However, when P was added to the soils, the first-order rate equation gave a satisfactory
description of the experimental data from soils derived from Shale and Basement complex,
indicating that P release rates in these soils were related to the quantity of P sorbed
reversibly to the surface. The rate coefficients varied widely among soils from the same
parent materials and between parent materials due probably to variations in the properties
of the soils. The rate coefficients from the Elovich equation, parabolic diffusion equation
and the fractional power model were best predicted from soil organic carbon (OC), clay,
pH, and extractable Al and Fe oxides. These soil properties together explained between 93
and 99% of the variance in the rate coefficients of P desorption in the soils.
Description
A THESIS SUBMITTED TO THE POSTGRADUATE SCHOOL, AHMADU
BELLO UNIVERSITY, ZARIA IN PARTIAL FULFILMENT OF THE
REQUIREMENTS FOR THE AWARD OF DEGREE OF MASTER OF SCIENCE
OF AHMADU BELLO UNIVERSITY, ZARIA.
DEPARTMENT OF SOIL SCIENCE
AHMADU BELLO UNIVERSITY, ZARIA
JULY, 2006
Keywords
KINETICS, PHOSPHATE, RELEASE, FOREST, SAVANNA, SOILS