Straw retention combined with phosphorus application improved soil properties, root nitrogen metabolism and optimized the relationship between root and shoot of cotton

Aims Straw retention combined with phosphorus (P) application has been proven to be an effective method to reduce the P application without decreasing cotton yield, but the related internal physiological mechanism of root is unclear. This study aimed to explore the impact of straw retention combined with different P application rates on soil nutrient content, the yield and quality of fiber, allometric growth relationship between root and shoot, and root nitrogen (N) metabolism. Methods The field experiment was conducted from 2020 to 2021 to study the effects of straw management (removal and retention) combined with different P rates (including 0, 100, and 200 kg P ₂ O ₅ ha ^− 1 ) on soil quality, different allocation of biomass, and N uptake and assimilation. Results The results showed that straw retention combined with P application contributed to improving lint yield and fiber quality synergistically. The result due to the fact that straw retention combined with P application increased the soil nutrient contents but decreased the bulk density of soil, creating favorable soil conditions for cotton growth. Compared to straw removal combined with 0 kg P ₂ O ₅ ha ^− 1 , improvement of physical and chemical properties of soil markedly increased the activities of nitrate reductase (10.5%-89.2%), glutamine synthetase (8.5%-80.5%), and glutamate synthase (3.0%-45.9%), which enhanced N uptake and assimilation. Additionally, the optimization of root N metabolism enhanced shoot growth of cotton by increasing the leaf area index and affecting cotton biomass allocation, which favored the formation of cotton square and flower, and boll. Conclusions Overall, straw retention combined with P application could improve soil physical and chemical properties and optimize the relationship between root and overground growth, which is conducive to the synergistic improvement of cotton yield and quality. Furthermore, straw retention combined with 100 kg P ₂ O ₅ ha ^− 1 was the best choice in the actual field agronomic practice of cotton production.