PHOSPHATE
SORPTION CAPACITY OF A CALCAREOUS SOIL
INFLUENCED
BY ACIDIFICATION.
Anas,
W.& Füleky, GY.and Tolner, L., University of Agricultural Sciences,
ABSTRACT
When water soluble phosphate compounds are
added to soils much of the P is rendered insoluble within a few hours. The
capacity of soils to retain phosphate varies widely and is influenced by many
factors. One of the many parameters that have been proposed to account for the
retention of phosphate by soil is thought to be pH. The changing of pH changes
both the phosphorus solubility and the surface properties of soil, which will
affect the phosphate adsorption maximum and the slope of soil solution-solid
phase phosphorus ratio.
The present work is concerned with a detailed
study and interpretation of the adsorption isotherms and sorption capacity
under different levels of acidification. The phosphate-buffering capacity also
was determined.
A calcareous loamy soil of pH
= 7.9 was used for this study. The soil was incubated with 0,
80 and 320 mgP.kg
soil for one month. Four acidity levels (pH 7.9, 7.3, 6.0
and 4.5) were adjusted by adding HCl and incubating the soil samples for
further one month. The adsorption isotherm curves were established after 24
hours equilibration, fitting the modified two-term Langmuir equation and the
modified Freundlich equation with 1/3 exponent. The phosphate buffering capacity
(PBC) was determined at 0, 0.2 and 10 mg.lequilibrium concentration.
Both functions gave a good fit. The two
surface Langmuir phosphorus adsorption isotherm is better for studying the
phosphorus adsorption maxima parameters, while the Freundlich equation is more
suitable for describing the parameters Q and (PBC).
The studying of adsorption maxima at
different pH levels (7.9-4.5), demonstrates that the big change of investigated
pH approximately did not change the P-adsorption maxima in the view of un- and
moderate fertilized samples (0 and 80 mgP.kg), while a close correlation was observed with P-320, where
the phosphorus adsorption maxima decreases with the decreasing of
acidification. At the same time this big change in acidification practically
didn't change the phosphate buffering capacity calculated from the adsorption
isotherms.
Key words: Acidification;
aqueous solutions; phosphorus fertilization; P-adsorption.