The Effect of pH Adjustment of Municipal Compost on its Enrichment with Plant Growth Promoting Bacterium "Enterobacter Cloacae"

Elemental and microbial enrichment of compost are basic solutions to increase its quality. The addition of beneficial bacteria and plant growth promoters are confirmed by various environmental aspects. The pH of compost is a critical factor affecting bacterial persistence. In this study, the municipal compost was sterilized and divided into two parts: compost with initial pH (5.6) and compost with pH adjusted to 7 by calcium carbonate addition. Incubation of compost with Enterobacter cloacae was performed with 109 CFU g-1 population. The moisture content of the compost adjusted to about 40% of the water holding capacity and the samples were kept in an incubator at 26 °C. The microbial counting and pH measurement were accomplished at 3, 15, 45, 75, 105, 135, 165 and 195 days after inoculation. The results of microbial counting showed that the effect of pH on bacterial viability in the compost was significant (p<0.01). Forty-five days after inoculation, the microbial count in non-amended compost declined to about 104 CFU g-1 while in the amended compost it was 109 CFU g-1. Regardless of the fluctuations of microbial population in non-amended compost, the bacterial population was 107 CFU g-1 in both divisions of compost after 135 days' incubation. The number of bacteria in amended and non-amended composts was below the standard limit (106 CFU g-1) after 165 and 140 days incubation, respectively.