Preparation of calcium-alginate microcapsuled microbial fertilizer coating Klebsiella oxytoca Rs-5 and its performance under salinity stress

Preparation of microcapsules for microbial fertilizer containing Klebsiella oxytoca Rs-5 was performed by the method of pore-coagulation bath in order to enhance the bacterial survival rate under salinity stress. In this study, sodium alginate (SA) and calcium chloride (CC) were used as wall materials for microencapsulation. The results showed that the microcapsules activity was best when the concentrations of SA and CC were 1.5-2.0% and 2.0%, respectively, and the volumetric ratio of SA and Rs-5 culture was 3:1. The particles sizes of microcapsules were concentrated in the range of 0.85-1.10 mm, measured by laser particle size analyzer. While the expansion coefficients of diameter and weight of these microcapsules were 1.35 and 1.80, respectively. The content of Rs-5 in microcapsules reached 1014 cfu/g, the embed rate was almost 100%. The bacteria released from microcapsules reached upto 1010 cfu/g when immersed in physiological saline for three weeks and kinetic release of viable cells was studied and simulated. It was found that some depressions and many small cracks on microcapsules surface observed by scanning electron microscopy contributed to bacteria release from microcapsules. The microcapsuled microbial fertilizers could promote the cotton growth better than the free cells under the same salty conditions in pot experiments.