Potential soil P mobilisation capacity—method development and comparison of rhizosphere soil from different crops

Background Phosphorus (P) deficiency is wide-spread in agricultural soils. In light of increasing P fertilizer costs, it is of interest to assess the capacity of soil microbes to mobilise native soil P and added P. There is currently no method to assess P mobilisation in situ. Methods The soil P mobilisation potential was assessed by incubating low P soil for up to 30 days with poorly available P sources; C and N were added to increase microbial activity and ensure that only P was limiting microbial growth. Results The increase in microbial P from day 0 to day 15 showed that microbes were able to mobilise P from FePO4 and phytate. The P mobilisation potential (sum of microbial and resin P) of the rhizosphere soil decreased in the following order: faba bean > chickpea and white lupin > wheat. After 10 days, up to 80% of the mobilised P was microbial P, whereas after 30 days, almost all P mobilised was resin P. Conclusions The method developed in this study is useful assessing not only potential of a soil to mobilise P but also, by using different poorly available P sources, the mechanisms of P mobilisation.