Rapid Bioconversion of Rice Straw Using Cellulolytic Cultures for Improved and Sustainable Crop Productivity and Soil Fertility in Mwea, Kenya
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Date
2018
Authors
Karanja, Anncarol W.
Journal Title
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Publisher
Kenyatta University
Abstract
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.
Description
A thesis submitted in fulfilment of the requirements for the award of the degree of Doctor of Philosophy (Microbiology) in the School of Pure and Applied Sciences of Kenyatta University. 2018