Effects of organic fertilizer combined with Pseudomonas fluorescein on maize yield and phosphorus activity in reclaimed soil

Reclaimed soil is characterized by the infertility and extremely low phosphorus content, thus severely impeding the growth and development of crops. This study aims to investigate the effects of chemical fertilizer and organic fertilizer combined with Pseudomonas fluorescein on phosphorus fractions and enzyme activity in reclaimed soil, in order to accelerate the soil reclamation in mining areas. A two-year targeted fertilization experiment was conducted in a coal mining subsidence area in Jinzhong City, Shanxi Province, China. Seven treatments were established: no fertilization control (CK), single application of chemical fertilizer (CF), chemical fertilizer combined with P. fluorescein (CFB), single application of organic fertilizer (M), organic fertilizer combined with P. fluorescein (MB), chemical fertilizer combined with organic fertilizer (MCF), and chemical fertilizer and organic fertilizer combined with P. fluorescein (MCFB). The soil samples were collected from the treatment plots. The phosphorus fractions, microbial biomass phosphorus, and soil phosphatase activity were measured after that. In addition, the correlation between soil phosphorus fractions and Olsen P was explored to construct the structural equation model between soil phosphorus fractions and microbial biomass phosphorus, acid phosphatase, alkaline phosphatase, and Olsen P. Results showed that: 1) Different fertilization treatments significantly increased the maize yield and various phosphorus fractions during the entire experimental period (2021-2022), compared with CK. Among them, the MB treatment was achieved in the highest maize yield, Olsen-P content, phosphorus activation coefficient (PAC) value, labile phosphorus (L-P), and moderately labile phosphorus (M-P) content. The maize yield, Olsen-P content, PAC value, L-P content, and M-P content increased significantly by 2.40, 4.50, 4.67, 0.98, and 1.16 times, respectively, compared with the CK treatment. 2) The application of chemical and organic fertilizer combined with P. fluorescein also increased the soil microbial biomass phosphorus and the activities of acid and alkaline phosphatase enzymes, in terms of microbial activity. After combined application with P. fluorescein, the levels of microbial biomass phosphorus and alkaline phosphatase enzyme activity were most effectively enhanced under the MB treatment, compared with the M treatment, indicating the significant increase of 27.08% and 9.56%, respectively. 3) The correlation analysis showed that there was the closest relationship between labile phosphorus forms (Resin-P, NaHCO3-Pi, and NaHCO₃-Po) and Olsen P. Furthermore, there was the much larger direct and positive effects of labile phosphorus on microbial biomass phosphorus, acid phosphatase, alkaline phosphatase activities, and Olsen P, according to the structural equation model. The large standardized path coefficient was found that the application of chemical fertilizer, organic fertilizer, and P. fluorescein on L-P was promoted the circulation and transformation of phosphorus in the farmland ecosystem, indicating a positive impact. In summary, the combined application of different fertilizers with P. fluorescein were promoted the yield and yield traits of maize in the reclaimed soil, together with the forms and availability of phosphorus, and microbial activity, indicating a positive impact on the fragile agroecosystem of reclaimed soil. Among them, the combined organic fertilizer with P. fluorescein significantly increased the Olsen-P content, L-P content, and M-P content, SMBP content, and ALP activity in the reclaimed soil, compared with the sole application of organic fertilizer. The finding can provide the more effective fertilization.