Effect of rice straw on the composition of volatile soil gas and micro flora in the tropical paddy field

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Abstract
The effect of rice straw on the composition of volatile soil gas and microflora in the tropical paddy field was studied with and without fertilizer application. The volatile soil gas most abundantly found in plots with rice straw was methane followed by other gases, nitrogen, oxygen and carbon dioxide during the early stage of rice growth, while nitrogen predominated in later stages. The loss of soil nitrogen through volatilization increased following phosphorus application as well as rice straw application as compared with that in the control plot. In the former case, the enhancement of decomposition of organic-N was assumed to be due to the increase in population of cellulose decomposer. Rice straw application with or without N-fertilizer increased methane gas formation by 27 to 63 times as compared with the phosphorus plot and the peak of its formation was found 5 to 7 weeks after rice straw application. However methane formation in the control plot was very low and was found only 5 to 9 weeks after flooding. Rice straw application usually increased the number of various groups of microorganisms along with contributing to the transformation of organic-N to N2 gas. But the stimulating effect was chiefly observed in the population of Azotobacter.