The effects of pH on phosphorus utilisation by chickpea (Cicer arietinum)

Abstract: Chickpea (Cicer arietinum) is known to secrete organic anions. We investigated its effectiveness in obtaining P over a range of pH values. Methods: We grew two cultivars of chickpea, supplied with either ammonium or nitrate nitrogen, at 10 levels of applied P, and at four initial pH values. We measured plant weight, P concentration in the tops, and rhizosphere pH. We compared the results with those previously obtained for lucerne (Medicago sativa), mustard (Brassica campestris) and rice (Oryza sativa). Results: Above an initial pH_CaCl2, of about 5, rhizosphere pH decreased; below this value it increased. The changes in pH were proportional to the amounts of P applied. They were greatest at high levels of applied P. Best growth occurred when the initial pH_CaCl2 was 5.9 and when the rhizosphere pH_CaCl2 was close to 5. Plots of growth against plant shoot P concentration showed little effect of low pH suggesting that aluminium toxicity was only of minor importance. Nevertheless, plant weight was severely depressed by low pH. Conclusions: The mechanism of P uptake for chickpea seems to differ from that for lucerne, mustard and rice. The way that the charge on the phosphate ions is balanced seems to depend on the soil pH. Further, uptake is much more markedly depressed by at low pH.