Microbiologists from the Faculty of Agriculture, University of Peradeniya have isolated indigenous soil bacteria and fungi that can accelerate the decomposition of rice straw in wetland rice fields.
Inoculant mixtures have been formulated with several bacteria and fungi. These inoculents can be recommended for fresh rice straw from new improved varieties used in wetland rice fields.
For more than four decades, high yielding rice varieties were widely grown with the use of chemical fertilizer in all rice cropping systems of Sri Lanka. However, yield stagnation of rice was recorded in many parts of the island in the early 80’s, due partly to the decreased fertility of rice soils.It has been shown that adding rice straw at a rate of 4 tons per hectare could provide the total potassium requirement and 30% of the nitrogen requirement of the rice crop.
Recycling of rice straw is not practiced by many farmers mainly due to high labour costs involved in bringing straw to the field and the difficulty in harrowing and ploughing the field in the presence of fresh straw. The best option to overcome this situation is to have the straw decompose quickly. However, under natural conditions, fresh straw should undergo decomposition for a period of about a month to become brittle. The slow decomposition of rice straw is due to its high lignin and cellulose contents. Only a few types of bacteria and fungi can decompose cellulose and lignin in rice straw. Therefore, speeding up of the decomposition process of rice straw by introducing such organisms would help overcome difficulties arising in land preparation for paddy cultivation.
The mixed inoculants of bacteria and fungi isolated by the researchers from the Faculty of Agriculture, University of Peradeniya decomposed straw rapidly with a weight reduction of up to 50% in 20 days. The decomposed material was also found to be high in nitrogen.
Incorporation of composted material in rice fields increased plant growth, number of tillers and yield under field conditions. Since these inoculants performed equally well at Kegalle in the absence of chemical fertilizer,and at Peradeniya in the presence of chemical fertilizer they could be recommended for both production systems.