Bacillus subtilis biofertilizer application reduces chemical fertilization and improves fruit quality in fertigated Tarocco blood orange groves

Abstract Rhizobacteria have been used for plant growth promotion of horticultural crops. In this field study, we evaluated the effects of liquid Bacillus subtilis commercial microbial fertilizer (BCMF) on fruit quality and plant nutrient status of fertigated citrus groves of Tarocco blood orange (Citrus sinensis (L.) Osbeck). A total volume of 600 mL BCMF per plant (containing over 2.0 × 108 colony-forming units (CFU) mL−1) was applied by diluted to 15 L through an integrated water and fertilizer irrigation system after the schedule of conventional fertilization (CF) of 100 % (CF100 + BCMF) and 50 % (CF50 + BCMF), and 15 L of clean water were used for irrigation after 100 % CF as the control treatments (CK). Both BCMF applications had positive correlation with fruit internal quality parameters, such as fruit maturity index (FMI), juice yield, edible rate, and per fruit weight (PFW), along with improved fibrous root density. However, the application of CF100 + BCMF delayed fruit peel and pulp coloring, and the highest nutrition partition ratio from soil to leaf of N (NNPRsl) and K (KNPRsl) and leaf nutrients concentration of N and K during harvest stage were achieved. In contrast, the CF50 + BCMF treatment led to a simultaneous color change in the fruit peel and the pulp along with a lower NNPRsl during the early stage of fruit ripening and leaf K concentration during fruit ripening due to the reduction of chemical fertilizer application as compared with the CK treatment. Meanwhile, the BCMF applications increased soil available P content and caused fruit titratable acids (TA) reduction. Our results suggest that the influence of B. subtilis biofertilizer application on fruit quality depends on the amount of the chemical fertilizers used, the application of biofertilizers contributes to reducing fertilizer input and exerts positive effects on the fruit quality in fertigated Tarocco blood orange groves.