Within field spatial variation in methane emissions from lowland rice in Myanmar

An assessment of within field spatial variations in grain yield and methane (CH(4)) 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 CH(4) measurements were conducted at the inlet, middle and outlet positions of each field. The results showed that CH(4) emissions at non-fertilized parts were higher than those at fertilized part in both rice fields. The average CH(4) emissions ranged from 8.7 to 26.6 mg m(-2) h(-1) in all positions in both rice fields. The spatial variation in CH(4) 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 CH(4) 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 CH(4) emission. The average CH(4) 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 CH(4) 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 CH(4) emissions required different site specific management practices to mitigate CH(4) emissions in lowland paddy rice soil.