Understanding extractable metal species relationships with phosphorus sorption and organic carbon in soils

Abstract

Context. Iron and aluminium oxides are important in phosphate sorption capacity of soils and preservation of soil organic carbon (SOC). However, there is a complex interplay between among Fe/Al oxides, SOC, and P in soils. Aims. We aimed to evaluate the relationships between extractable Fe and Al, SOC concentration and P sorption capacity using generalised additive mixed models. Methods. We compiled and analysed data from 77 published articles from Scopus and Web of Science. Key results. Ammonium oxalate extractable aluminium (Alox) had astrong significant relationship (P < 0.0001) with P sorption capacity, but this was stronger with dithionite-citratebicarbonate extractable aluminium (Ald). A positive 1:1 relationship between Alox and Ald suggests that the pool of Al dissolved by ammonium oxalate and dithionite citrate bicarbonate (DCB) was nearly similar. A strong significant relationship was found between ammonium oxalate extractable iron (Feox) and Alox, and SOC concentration, but Alox had a stronger statistically significant relationship with SOC concentration. This may be due to various interactions of SOC with Al oxides, which can directly or indirectly influence P sorption capacity in soils. Conclusions. From these relationships, we show that: (1) that Ald is a better predictor for P sorption capacity than Alox; and (2) Alox is a better predictor of SOC than Feox. Implications. DCB and ammonium oxalate extractable Al (and Fe) that represent Al in crystalline and poorly crystalline, or amorphous form of Al may be used as a routine soil test, and may be able to predict P sorption capacity and SOC preservation potential, particularly in acid soils.