Manure application enhanced cotton yield by facilitating microbially mediated P bioavailability

Low soil phosphorus (P) availability affects cotton (Gossypium hirsutum L.) yield in arid regions with saline soils, such as Central Asia, due to P sorption by soil particles and precipitation by Ca2+. P-based organic amendment is one potential solution to improve soil P bioavailability by influencing soil microbial processes, although the mechanisms behind this process are unclear. The aim of this study was to evaluate the influence of soil P availability on cotton production by microbially mediated P mobilization processes under P-based organic amendment conditions in saline soil. We analyzed the microbially mediated P mobilization and lint yield of a six-year field experiment with P-based organic amendment for manure or straw in Xinjiang, China, the largest oasis-type agricultural region with saline soil in Central Asia. There were seven treatments as follows: CK, without P application; the P1, 32.7 kg ha-1 mineral P application; St, straw return (containing 36.0 kg P ha-1); the P2, 65.5 kg ha-1 mineral P application; M, manure (containing 65.5 kg P ha-1); the P3, 131 kg ha-1 mineral P application, and DM, manure (containing 131 kg P ha-1). The M and DM treatments enhanced the microbial biomass phosphorus (MBP) pool by 71%− 270% and increased the phoD gene-harboring bacterial α diversity and abundance of phoD genes. The relative abundances of Pseudomonas, Amycolatopsis, and Streptomyces increased by 0.8–4.4 fold. As a result, alkaline phosphatase activity and subsequently P bioavailability increased. Compared with a similar mineral P application rate, the M treatment enhanced shoot P content by 7%, but there was an absence of differences in the St or DM treatment, and the lint yield in the M and DM treatments was increased by 10% and 16%, respectively. Manure application in saline soil can enhance soil P bioavailability by enlarging the MBP pool and improving alkaline phosphatase activity by enriching the phoD gene-harboring bacteria Streptomyces and Amycolatopsis and therefore improving P uptake and lint yield. Organic amendments such as manure may be an effective P management practice for improving cotton P uptake and lint yield in mulched fertigation cotton systems in saline soil.