Rapid Bioconversion of Rice Straw Using Cellulolytic Cultures for Improved and Sustainable Crop Productivity and Soil Fertility in Mwea, Kenya
Karanja, Anncarol W.
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Proper management strategies for huge amounts of crop residue generated from agricultural farms need to be obtained. Composting is a good strategy in rice straw management. Traditional methods of composting rice straw are limited in timely production of good quality compost due to its recalcitrant nature. There is need to develop and formulate microbial starter cultures that are adapted to local climatic conditions to ensure efficiency in using microorganisms in composting. This study aimed at assessing and presenting appropriate starter cultures for bioconverting rice straw into bioorganic fertilizer for use in crop production. Bacteria and fungi with lignocellulolytic potential were isolated and used alongside other starter cultures to enhance bioconversion of recalcitrant and abundant rice straw in Mwea, the main rice producing area in Kenya. The microbial isolates were selected through screening procedures and then characterized morphologically, biochemically and genetically. Rice straw was composted by treating it with the selected microorganisms, chicken droppings, commercial effective microorganisms and donkey dung in separate setups. The resultant compost types were characterized in respect to their maturity, heavy metal content and nutrient concentrations. Changes in microbial population densities and diversity during a natural composting process were also studied. The lignocellulolytic microorganisms selected for use in composting the rice straw in this study included 20 bacterial and 11 fungal isolates. Results from various identification techniques used showed that most of the bacterial isolates belonged to Genus Bacillus while most of the fungi were mainly in Genus Trichoderma. Mean values for temperature, pH and electrical conductivity (EC) among the five treatments of the study revealed significant differences at 5 % level of confidence. Using the starter cultures of the study, composting the rice straw was successfully completed within 62 days. The five compost types produced by the composting experiments were physicochemically different as demonstrated by the significant differences revealed by analysis of variance (ANOVA) of their cation exchange capacity, phosphorus, nitrogen and carbon content. The composts were observed to have attained biological maturity as revealed by the germination index, plant growth index and C: N ratio values recorded. Microbial analysis of compost samples taken from the natural composting experiment indicated notable variations in the number of bacterial cells at different phases of composting ranging from 8.7 x 105 to 2.1 x 106 CFU/ g. It was observed that fungi were less prevalent in the compost during the thermophilic phase with a lower overall prevalence compared to bacteria. Bacteria were most predominant in the compost having 28 different bacterial isolates against 17 fungal isolates. Results indicated that addition of the selected lignocellulolytic bacteria and fungi and various starter cultures significantly improved the composting process and the quality of the resultant composts. The experiment on natural composting process showed that variations in microbial population densities and diversity correspond to fluctuations in temperature within the composting materials. From the findings of this study, it is recommended that the obtained lignocelluloytic microorganisms be formulated and used for composting plant residue and other organic wastes to enhance the composting process and improve the quality of resultant bioorganic fertilizers.