Influence of pH on a secondary effect of phosphate reaction: The decrease in sorption of newly added phosphate

Secondary effects occur as a consequence of previous applications of phosphate to soil. They are caused by the decrease in charge and potential resulting from reaction of phosphate with soil. Such effects on the sorption of newly added phosphate were largest between about pH 3.5 and 5.0. At higher pH, the smaller effects are ascribed to the fact that the potentials are already low and the extra effect of phosphate is small. At lower pH, previously sorbed phosphate was more readily desorbed. It is suggested that this increased lability means that the secondary effects are decreased.