A four-year project, entitled “The mechanisms of fraction transformation and high use efficiency of P fertilizer in Chinese cropping systems” commenced in 2017. The project was established to answer three key questions and looked at 17 cropping systems on ten soils. First, we asked what are the dynamics of transformation, fixation and mobilization of P fertilizers in soil-cropping systems? Second, what are the mechanisms of soil-crop-microbe interactions by which P fertilizer can be efficiently used? Third, how to manipulate the processes of P use in cropping systems? The targets of this project are (1) to explore the mechanisms of P fixation, the pathways of loss of P availability and the threshold of migration of fertilizer P in the field; (2) to uncover mechanisms by which soil legacy P is mobilized through root physiological and morphological processes and through arbuscular mycorrhizal fungi and P-solubilizing bacteria in rhizosphere and hyphosphere; (3) to estimate the biological potential of crops for high efficiency P absorption and use; (4) to innovate new approaches for improving the efficiency of P fertilizers. The outcomes will provide theoretical support for setting standards for limitation of P fertilizer application rate in the main cropping zones of China.