Abstract

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.

Published in

Soil Science Society of America Journal
2020, Volume: 84, number: 3, pages: 994-1005

SLU Authors

• Blombäck, Karin

  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Soil Science


Publication identifier

DOI: https://doi.org/10.1002/saj2.20078

Permanent link to this page (URI)

https://res.slu.se/id/publ/108883