Can optimization of phosphorus input lead to high productivity and high phosphorus use efficiency of cotton through maximization of root/mycorrhizal efficiency in phosphorus acquisition?

Although the root/mycorrhizal processes determine phosphorus (P) uptake by crops and P fertilizer use efficiency, knowledge of the plasticity of cotton root/mycorrhizal processes in response to changes in soil P content is lacking. A field experiment was conducted in 2015 and 2016 to investigate the effects of P fertilizer treatments (0, 75, 150, and 300 kg P2O5 ha−1) on root/mycorrhizal processes and P uptake by cotton plants. The main aim was to explore the possibility of achieving high P fertilizer use efficiency and high yield simultaneously by optimization of P fertilizer application. A low P application rate (75 kg P2O5 ha−1) not only increased root length and hyphal density simultaneously, but also enhanced the spatial distribution of cotton roots in the soil, thereby also increasing the apparent phosphorus recovery (APR). However, P uptake and cotton yield were highest under treatment with 150 kg P2O5 ha−1. Thus, it is difficult to maximize APR and cotton yield simultaneously. If the production target is to obtain a relatively high yield (80-90% of the highest potential yield), then root/mycorrhizal efficiency in P acquisition can be maximized through optimization of the soil available P content. The optimum soil available P content observed in this study was 15-20 mg kg−1.