Effect of Application of Rice Straw and Cellulose on Methane Emission and Biological Nitrogen Fixation in a Subtropical Paddy Field

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Abstract
A field experiment was conducted to evaluate the effect of the incorporation of rice straw and cellulose on methane flux, soil-acetylene reduction activity (ARA) and rice plant growth under a subtropical climate. Rice straw and cellulose (as paper) were applied at the rates of 4 and 10 t ha-1. Emission rates of CH4 from the paddy field without and with straw and cellulose amendments were measured by using the closed chamber method. Stimulation of N2-fixation by the amendments was measured as soil-ARA under anaerobic conditions. The measurements indicated that the application of 10 t ha-1 cellulose resulted in a relatively high emission of CH4, with an average flux of 106.7 mg CH4 m-2 h-1, followed by 10 t ha-1 straw, 51.7 mg m-2 h-1, compared with the control, 5.3 mg m-2 h-1. Application of straw and cellulose at the rate of 10 t ha-1 to the paddy field increased the CH4 emission 10 and 21 fold over the values of the control, respectively as estimated seasonal emissions. The soil-ARA levels in the treatments during the cultivation period were positive. The stimulation of ARA by the amendment with 10 t ha-1 cellulose occurred at the early stage of rice growth, while the maximum ARA-peak occurred in the 10 t ha-1 straw-amended soil at around the heading stage. Amendment with straw at 10 t ha-1 significantly increased the total dry matter weight of rice, whereas growth inhibition was induced by cellulose incorporation. The differences in CH4 flux, and soil-ARA among the treatments were most evident at the heading stage.