IMPACT OF GYPSUM APPLICATION ON THE METHANE EMISSION FROM A WETLAND RICE FIELD

Methane emission from Philippine rice paddies was monitored with a clo sed chamber technique during the 1991 and 1992 wet season. The methane emission from plots amended with 6.66 tons.ha-1 gypsum was reduced by 55-70% compared to non-amended plots. Although CH4 emission from fiel ds with a high input of fresh organic matter was strongly enhanced, th e experiments showed that the relative reduction in CH4 emission upon gypsum application was independent of organic matter addition. The red uced CH4 emission upon gypsum application was most likely due to inhib ition of methanogenesis by sulfate-reducing bacteria. Observed SO42-co ncentrations in the soil solution of gypsum-amended plots were well ab ove minimum concentrations reported in the literature for successful c ompetition of sulfate-reducing bacteria with methanogens. The data pro vide a base for reducing the estimates of CH4 emissions from rice grow n on high-sulfate containing soils or gypsum-amended soils.