POPULATIONS OF METHANOGENIC BACTERIA IN PADDY FIELD SOIL UNDER DOUBLECROPPING CONDITIONS (RICE-WHEAT)

The methanogenic populations able to use H-2-CO2, methanol, and acetat e were investigated in paddy dy field soil in situ under double croppi ng conditions [rice (Oryza sativa L.) as a summer crop under flooded c onditions and wheat (Triticum aestivum L.) as an upland winter crop] o ver 2 years approximately bimonthly by the most probable number method . Three fields, one without fertilizer, one treated with inorganic fer tilizer (mixed fertilizer including urea, ammonium phosphate, and pota ssium sulfate), and one treated with wheat straw plus inorganic fertil izer, were examined. The population of H-2-CO2, methanol, and acetate utilizers in the paddy field soil at a depth of 1-6 cm was 10(3)-10(4) , 10(4)-10(5), and 10(4)-10(5) g(-1) dry soil, respectively. These val ues were almost constant during the 2 years irrespective of moisture r egime (flooded or nonflooded), crop (rice or wheat), fertilizer treatm ent, and soil depth (0-1, 1-10, and 10-20 cm).