Experimental results revealed that there were always nitrificating activities in flooded rice-field soils,whether the soils were under rice crops to summer or were kept barren in winter.Quantities of nitrifing organisms found in flooded rice-field soils were much higher than those in dry-land crop soils,the difference being between 23-377 times,according to the data.In the rice-field soils, nitrifying organisms were active not only in the more oxidative "oxidation horizon",but also in the more redutive "reduction horizon",The results contrary to the "classical" notion that the nitrifying organisms could not live actively in the flooded rice-field soils.