Page 27 - Volume 2, Issue 1, January 2009

© Benaki Phytopathological Institute
Effect of superphosphate on glyphosate adsorption in soil 27
tilizer in the above experiments was 0.3 g
of the 0-20-0 granular formulation per 100
g of soil. This corresponds to a supply of
about 260 ppm of P which is well in excess
of the recommended P fertility level of up
to 50 ppm (1). It is of interest that at this su-
perphosphate rate, at which P is assumed to
maximally compete glyphosate for the soil
adsorption sites, adsorption of glyphosate
was not actually reduced.
In another series of experiments in which
various levels of superphosphate fertiliza-
tion were utilized, the increased adsorption
by the soils KA1 and H1 was observed at all
superphosphate levels tested (0.25, 0.5 and
1.0%) and with both glyphosate and AMPA
(Figure 2). This effect of superphosphate in
soils KA1 and H1 was most pronounced at
high glyphosate and AMPA concentrations
and this is consistent with the high adsorp-
tion capacity of these two soils. It is of in-
terest, therefore, that in these two soils in
Figure 2. Glyphosate and AMPA adsorption on KA1 and H1 soil samples that had been previously amended with the in-
dicated 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.