Combined Chemical Fertilizers with Molasses Increase Soil Stable Organic Phosphorus Mineralization in Sugarcane Seedling Stage

The lack of available phosphorus (P) in red soil severely limits the high yield of sugarcane. This study aims to explore the effects of different fertilization methods on P forms and bacteria community and the role of soil bacteria in P transformation in the seedling stage of sugarcane. Five fertilization treatments were set: no fertilizer (CK), a single application of chemical fertilizer (F), and combined application of chemical fertilizer with molasses (FC): the amount of added molasses (mg C kg −1 soil) was 64 (FC1), 160 (FC2), and 240 (FC3). Compared with F, FC treatment increased the sugarcane dry biomass, soil organic matter (SOM), pH, soluble organic P (Po) and stable inorganic P (Pi) contents while decreased the stable Po contents. All the F and FC treatments decreased the Shannon index compared with CK, whereas FC2 increased the Chao1 index and observed species. Proteobacteria , Chloroflexi, and Actinobacteria were the dominant taxa in all five treatments, where the relative abundances of Firmicutes and WPS-2 were higher in F than in FC. The increases in Bacillus and Sinomonas were accompanied by the depletion of soil stable Po. Redundancy analysis (RDA) revealed that pH and AP levels were significantly related to the bacterial community structure. Besides, the relative abundances of Bacillus plus Sinomonas were positively correlated with sugarcane dry biomass. These findings indicated that combined application of chemical fertilizer with moderate molasses can increase the sugarcane biomass and promote the utilization of soil stable Po via altering bacteria community and soil properties.