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.