PHOSPHATE SORPTION CAPACITY OF A CALCAREOUS SOIL

INFLUENCED BY ACIDIFICATION.

 

Anas, W.& Füleky, GY.and Tolner, L., University of Agricultural Sciences, Gödöllô, Hungary

 

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.