Adding three protein resources as solid-state fermentation medium for producing bio-organic fertilizer

【Objectives】It has been extensively demonstrated that bio-organic fertilizer (BIO) could eventually replace some of the chemical fertilizers and pesticides that are currently overused in agriculture, enhance stress tolerance of plants, improve crop quality and soil quality, and so on. Meanwhile, the application of these BIOs is becoming more popular since more and more farmers are recognizing the effect of BIOs not only in promoting plant growth but also in protecting plant roots from soil-born pathogens as well. In addition, number of functional microbes play a key role for producing the best effects. Thus, in order to improve quality of the produced BIO, addition of amino acids as solid-state fermentation (SSF) medium is a main method for producing BIOs with functional microbes. However, the production costs significantly are increased due to high cost of oil rapeseed cakes which is the common exogenous amino acids till now, thereby limiting the large-scale extension of BIOs. Therefore, new SSF media should be developed to greatly reduce the production cost while supplying essential nutrition for the special microbial species and to further promote efficacious plant growth. 【Methods】This study investigated possibility of producing the BIO with PRPG strain Bacillus amyloliquefaciens SQR9 by adding rapeseed cake and two high-protein solid wastes, algal sludge and feather powder, in cow dung compost using the single-factor test and orthogonal experiment. 【Results】The single-factor test results show that the optimum inoculum volume and moisture content are 7.5% and 40%, respectively. The orthogonal test reveals that the cell density of strain SQR9 could reach up to 3.88108 CFU/g (DW) in the optimum combination consisting of 5% algal sludge, 8% rapeseed and 12% feather powder after 7 days of SSF, the contents of total free amino acids and short peptides TAPS in the resulting BIO could reach up to 1.39% (DW), and the values are both higher than those in the control product produced with none exogenous amino acids, meanwhile, the content of total nitrogen is also higher. The pot experiment results indicate that the BIO application efficiently promotes the plant growth. Forty days after being applied to the cucumber and eggplant plants, the novel BIO treatment results in greater plant heights, stem diameters and SPAD values compared to the two controls. Compared with the BOF treatment, the BIO treatment increase the above- and below-ground fresh weights of cucumbers by 51.15% and 19.59%, the above- and below-ground dry weights of cucumbers by 4.59% and 22.66%, the above- and below-ground fresh weights of eggplants by134.29% and 29.73% and the above- and below-ground dry weights of eggplants by72.35% and 43.69%. Compared with the OF treatment, the BIO treatment increases the above- and below-ground fresh and dry weights of cucumbers by 65.56%, 33.39%, 17.89% and 39.18% and the above- and below-ground fresh and dry weights of eggplants by 154.01%, 38.03%, 78.95% and 78.13%, respectively. 【Cconclusion】The addition of high-protein solid wastes and rapeseed cake could effectively promote the SFF with the functional microbe and improve the fertilizer quality. This research also provides a novel way of cyclic utilization of algal sludge and feather powder, and technology supports for exploring PGPR products and novel low-cost but high-quality BIOs.