Maximising cotton phosphorus utilisation for zero surplus and high yields: A review of innovative P management strategies

Cotton (Gossypium hirsutum L.) is one of the most salt-tolerant cash crops in the arid zone of Central Asia, especially in Xinjiang (XJ), China. Phosphorus (P) deficiency is one of the major yield-limiting factors for cotton production in this region. Although a high-chemical-P fertiliser input ensures high yields, only 18% of P can be taken up by crops in the application season, leading to large economic losses for farmers and accelerating the depletion of non-renewable P resources. It is a great challenge to optimise P inputs, increase P use efficiency (PUE) and maintain high yields under mulched fertigation cotton production systems. This paper aims to review the current efforts to improve PUE for cotton production in XJ and to provide feasible insights into nature-based solutions for high-P utilisation of cotton in the future. We focused on the following: (ⅰ) identifying the main factors that lead to the low PUE of cotton in XJ and the potential influencing mechanisms, (ⅱ) exploring innovative P management options to maximise the biological potential for improving high-P utilisation and reducing soil P surplus in mulched fertigation cotton production systems, (ⅲ) providing future perspectives of high P utilisation in mulched fertigation cotton production systems. We conducted a systematic literature search on the Web of Science and China National Knowledge Infrastructure (CNKI) to review publications that are related to the topic of cotton yield and P utilisation under different P management practices with field experiments in XJ. On the basis of the research, we proposed new insights into improving P management practices in mulched fertigation cotton production systems. We found that the soils exhibited a significant capacity for P fixation with high pH and carbonate content in XJ, leading to poor P migration when drip-irrigated. A mismatch between P fertiliser types and soil crop systems further hindered P absorption by cotton. Moreover, excessive P application and limited biological processes for soil P cycling impeded improvements in PUE. Therefore, we emphasised the importance of the root/mycorrhizal pathway in cotton P uptake and suggested using the high mycorrhizal dependence and P-efficient cotton genotypes, maximising the biological potential of the root morphology, mycorrhizal symbiosis, P-solubilising microorganisms and microbial biomass P (MBP) pool turnover in soil P mobilisation, which could increase cotton P uptake and PUE. Furthermore, we proposed a strategy of using starter P combined with ammonium sulfate fertigation after the plant emergency, and concentrated application of acidic P fertiliser with the pursuit of ammonium sulfate could achieve high cotton yields and P fertiliser efficiency. We also highlighted the potential of organic amendments in enhancing soil P bioavailability and P recycling by enlarging the MBP pool and improving the alkaline phosphatase activity, thus improving cotton P uptake and yield. Finally, we noted that nature-based solutions, which were commonly neglected in previous studies, should be integrated into zero-P surplus management strategies to maximise the biological potential for high-P utilisation in cotton production. The use of organic amendments enhanced the biological potential for the high-P utilisation of cotton. Combining starter P fertiliser with ammonium sulfate induced rhizosphere acidification and increased cotton yields and PUE. In addition, integrating nature-based solutions into zero-P surplus management strategies can increase cotton PUE and can maintain a high yield by maximising the biological potential for high-P utilisation. Overall, developing novel P management practices to optimise nature-based soil P cycling and to improve the biological potential for zero-P surplus can maximise the high yield and can underpin sustainable cotton production in an arid zone.