Effect of pH and some organic anions on the solubility of soil phosphate: implications for P bioavailability

Berlin

1996

S. 231-239

4 Abb., 2 Tab., 40 Lit. Ang.

Artikel aus einer ZeitschriftUnselbständiges Werk

200152546

The effect of pH and the addition of carboxylates (acetate, oxalate, tartrate, salicylate and citrate) on the solubility of soil phosphate has been investigated to assess the possible effects of root exudates on phosphate availability. The soil was a neutral calcic Luvisol with a large pH buffer capacity. Various concentrations of strong acid (0–20 mmol kg−1) and anion (0–2 mmol kg−1) were applied to soil in suspension (0.5 g soil cm−3). The effect of 2 mmol kg−1 oxalate on the adsorption isotherm of phosphate was also studied. The rate of isotopic exchange was largely unchanged by any of the treatments. Neither pH nor acetate had an effect on phosphate solubility. The addition of di– and trivalent anions increased phosphate solubility somewhat. The effect increased with increasing concentration of anion, and was generally independent of pH and the proportion of anion adsorbed. Oxalate was more efficient in limiting the adsorption of freshly added phosphate than in desorbing native phosphate. The results illustrate that rhizosphere acidification does not necessarily increase phosphate solubility. However, carboxylates, the conjugate bases of organic acids, may play an important role in improving the availability of soil phosphate.