Microbial Communities and Their Activities in Paddy Fields: a Review

A paddy field is a flooded parcel of land used for growing rice and other semi-aquatic crops e.g. water lettuce. Depending on the environmental conditions, five distinctive types are recognized namely; irrigated, rain-fed/lowland, deep water, upland and tidal environments. Microorganisms found in paddy field soils include bacteria, fungi, viruses, protozoan and actinomycetes. However, bacteria are the most prominent microorganisms. Microorganisms present in rice rhizosphere exhibit several ecological relationships between one another and rice roots. These may be detrimental e.g. competition, predation and immobilization of elements or beneficial e.g. syntrophism, commensalism and saprophitism. The major microbial activities in paddy field include methanogenesis, methane oxidation and biogeochemical cycling of elements. Some of the factors that influence microbial activities in paddy fields are quality and quantity of organic materials, pH, oxygen availability, temperature, seasonal variation, rice cultivars, moisture status, inorganic fertilizers and the presence of inhibitory substances. Paddy fields are among the leading producers of methane, contributing about 10% of all global emissions. Paddy field workers are exposed to many health hazards such as Ascaris infection, diarrhea, schistosomiasis, skin irritation and tetanus infection. Paddy field workers should therefore, use foot wears, hands gloves and observe adequate personal hygiene when working in the field in order to prevent the various hazards.