An assessment of within field spatial variations in grain yield and methane (CH4) emission was conducted in lowland rice fields of Myanmar. Two successive rice fields (1(st) field and 2(nd) field) were divided into fertilized and non-fertilized parts and CH4 measurements were conducted at the inlet, middle and outlet positions of each field. The results showed that CH4 emissions at non-fertilized parts were higher than those at fertilized part in both rice fields. The average CH4 emissions ranged from 8.7 to 26.6 mg m(-2) h(-1) in all positions in both rice fields. The spatial variation in CH4 emission among the positions was high in both rice fields with the highest emissions in the outlet of the 1(st) field and the inlet of the 2(nd) field. The CH4 emissions at these two positions showed 2 - 2.5 times higher than those at other positions in both rice fields. Stepwise regression analysis indicates that soil total carbon content is the primary factor for CH4 emission. The average CH4 emissions during rice growing season were 13.5 mg m(-2) h(-1) for the 1(st) field and 15.7 mg m(-2) h(-1) for the 2(nd) field. Spearman rank order correlation analysis showed that CH4 emission was significantly and positively correlated with soil temperature, surface water depth and negatively correlated with soil redox potential. The result indicated that high within field spatial variation in CH4 emissions required different site specific management practices to mitigate CH4 emissions in lowland paddy rice soil.
Keywords: Fertilizer; Lowland rice; Methane emission; Soil properties; Spatial variation.