Abstract. Mineral P is an increasingly scarce resource and therefore the mobilisation of legacy soil P must be optimised to maintain soil fertility. We have used isotopic exchangeability to probe the lability of native soil P in four contrasting soils following acidification and the addition of carboxylate anions (citrate and oxalate) in soil suspension. Acidification tended to cause immobilisation of soil P, but this was attributed to a salt effect. Addition of both citrate and oxalate led to marked increases in mobilisation of soil P. This would result from both competition between carboxylate and phosphate ions at adsorption sites and chelation of charge compensating cations. The carboxylate effects were similar at each level of acidification, indicating that effects were largely additive. This is not true for the most calcareous soil where calcium oxalate may have been precipitated at the highest oxalate addition. Promoting carboxylate anions in soil by soil amendment or the use of crops that exude large amounts of such organic anions is a promising approach to improve soil P availability.

中文翻译：

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同位素交换性揭示土壤磷酸盐被羧酸根阴离子动员，而酸化则产生相反的效果


摘要。矿物磷是一种日益稀缺的资源，因此必须优化遗留土壤磷的利用以维持土壤肥力。我们利用同位素交换性来探讨四种对比土壤在酸化和在土壤悬浮液中添加羧酸根阴离子（柠檬酸根和草酸根）后原生土壤磷的稳定性。酸化往往会导致土壤磷的固定，但这归因于盐效应。添加柠檬酸盐和草酸盐导致土壤磷的移动显着增加。这是由于吸附位点处的羧酸盐和磷酸盐离子之间的竞争以及电荷补偿阳离子的螯合造成的。在每个酸化水平下，羧酸盐的影响相似，表明影响很大程度上是相加的。对于钙质最多的土壤来说，情况并非如此，因为草酸钙在草酸盐添加量最高的情况下可能会沉淀。通过土壤改良剂或使用散发大量有机阴离子的作物来促进土壤中的羧酸根阴离子是改善土壤磷有效性的一种有前景的方法。