Summary
This comparative study evaluated four different approaches to calculating phosphorus saturation indices as simple field-applicable indicators of soil P leaching risk to sensitive water bodies. Both ammonium oxalate-derived (AlOX + FeOX) and PSI-based methods showed strong correlation with fitted Langmuir sorption capacity, whilst ammonium lactate-derived estimates did not. The findings demonstrate that multiple DPS calculation methods can effectively predict a soil's propensity to release dissolved phosphorus, providing practitioners with flexibility in method selection for identifying phosphorus leaching hotspots.
UK applicability
These findings are applicable to UK agricultural practice and environmental regulation, particularly in regions with intensive farming and P-sensitive water bodies. The flexibility in DPS calculation methods could support UK soil testing laboratories and farm advisers in adopting practical P saturation screening protocols aligned with diffuse pollution risk assessment and nutrient management planning requirements.
Key measures
Four DPS indices: (AlOX + FeOX), (AlAL + FeAL), PSI with PAL, and PSI with POls; dissolved P measured by CaCl2 extraction (PCaCl2) and deionised water extraction (PW); Langmuir sorption maximum (Smax); single point P sorption index (PSI); clay content, pH and total carbon
Outcomes reported
The study compared four different degree of phosphorus saturation (DPS) indices in their ability to predict dissolved phosphorus (measured as PCaCl2 and PW) in soil extracts. It evaluated how well various methods for estimating phosphorus sorption capacity correlated with Langmuir sorption maximum values.
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