The single‐point P sorption index (PSI), which is defined as the ratio of sorbed P (S) to the log P concentration in soil solution following a single P addition, is often used to estimate maximum soil P sorption capacity (S_max). Although studies have found good correlations between PSI and S_max as determined from fitting the Langmuir model to complete sorption isotherm data, a thorough analysis of the role of added P concentration on this relationship is needed. Our first objective was to investigate the effect of added P concentration on the correlation between PSI and S_max as determined by the Langmuir equation. Our second objective was to determine if S was better than PSI for predicting S_max. Using numerical simulations, we tested the correlation between S_max and PSI for added P concentrations of 75, 100, 150, and 200 mg P L⁻¹. Results of the simulations show that the strength of the correlation between S_max and PSI increases with increasing P concentration. Our results also show that PSI was a better predictor of S_max than S for added concentrations of 75 and 100 mg P L⁻¹, whereas at the higher rates S was a slightly better predictor of S_max and gave a direct estimate of S_max rather than the relative estimate obtained from PSI. Results from P sorption data measured on soils from Maryland and Sweden were consistent with our results from the numerical simulations. Our findings highlight important limitations of using PSI for estimating S_max.

中文翻译：

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评估磷吸附指数对估算最大磷吸附量的有效性

单点P吸附指数（PSI），其被定义为吸附的P（比例小号）下列单P加成土壤溶液中的log P浓度，通常用于估计最大土壤磷吸附能力（小号_最大）。尽管研究发现，通过拟合Langmuir模型到完整的吸附等温线数据可以确定PSI和S _max之间具有良好的相关性，但仍需要对添加的P浓度在这种关系上的作用进行全面的分析。我们的首要目标是研究通过Langmuir方程确定的添加P浓度对PSI和S _max之间相关性的影响。我们的第二个目标是确定S是否预测S _max优于PSI 。使用数值模拟，我们针对添加的75、100、150和200 mg PL ^-1的P浓度测试了S _max与PSI之间的相关性。模拟结果表明，S _max与PSI之间的相关强度随P浓度的增加而增加。我们的研究结果还表明，PSI是一个更好的预测小号_最多比小号为75和100添加浓度毫克PL ^-1，而在更高的数据速率小号是稍好的预测小号_最大，给直接估计小号_最大而不是从PSI获得的相对估算值。在马里兰州和瑞典的土壤上测得的P吸附数据结果与我们的数值模拟结果一致。我们的发现突出了使用PSI估算S _max的重要局限性。