Extractant efficacy in assessing bioavailable phosphorus in tropical soils fertilised with alternative sources and cultivated with maize

Context Phosphorus (P) is a vital element for plant growth across all soil types. In highly weathered soils, P levels are frequently insufficient, with detrimental impacts on plant development and crop yields. There are various methods to analyse soil P availability, each providing unique insights into its availability and dynamics under different soil conditions. Aims Our objective was to systematically evaluate the effectiveness of different P extractants in quantifying the available P in two soil types with contrasting textures. Additionally, the influence of different P fertilisers on the extraction efficiency of these extractants was assessed. Methods Three extraction methods were evaluated to predict plant-available P: resin, Mehlich-1, and Mehlich-3. A sandy loamy and a clayey soil were amended with organomineral, struvite, thermophosphate, and triple superphosphate under greenhouse conditions, and two successive maize crops were grown. Key results The resin method had the highest correlation with plant P uptake, showcasing its effectiveness for highly weathered soils. Mehlich-1 and Mehlich-3, however, seemed to overestimate P values, likely because they dissolved soil minerals and organic matter, and released P bound to colloid surfaces. Conclusions Extractant efficiency varied depending on the P fertiliser source applied. Additionally, lime rates affected extractant performance, especially Mehlich-1, due to interactions between acid P extractants and calcium-bound P. Implications This study underscores the importance of selecting the appropriate P measurement method for effective agricultural management and environmental conservation.