Page 28 - Volume 2, Issue 1, January 2009

Giannopolitis & Kati

28

which adsorption is increased with the ad-

dition of supephosphate, the rate of super-

phosphate does not seem to be as critical as

the rate of glyphosate and AMPA. It is also

worthy to note that soil H1 was found to ad-

sorb more glyphosate than AMPA while the

reverse was observed with soil KA1.

The same experiments with the soils H3

and K1, which are of a low adsorption capac-

ity (a sandy and a calcareous soil, respec-

tively), indicated that superphosphate at all

tested levels had only a slight decreasing or

increasing effect on glyphosate and AMPA

adsorption which could be seen only at low

concentrations of the two chemicals (Figure

3). Again, the rate of superphosphate is not

so critical as that of glyphosate and AMPA.

The addition of increasing concentra-

tions (0.25, 0.5 and 1.0%) of superphosphate

had also a parallel decreasing effect on the

pH of the soils (Figure 4). In soils KA1 and H1

in which adsorption is increased with the

addition of superphosphate, the pH was ac-

tually lowered to values which are more fa-

Figure 3

. Glyphosate and AMPA adsorption on K1 and H3 soil samples that had been previously amended with the indicat-

ed amounts of superphosphate and let to equilibrate for 5 days. Glyphosate and AMPA adsorption was measured by batch

equilibration experiments utilizing 10 ml/g of solutions at the proper concentrations to supply the indicated amounts of

each chemical.