Effect of anionic heavy metals on ammonification and nitrification in soil

Several experiments were carried out to analyze the effect of anionic heavy metals and chromium chloride on the activities of microorganisms. 1) Azotobacter and Fusarium were cultured in a liquid medium containing 5, 25, and 125 μm of each heavy metal and the changes in the optical density in relation to microbial growth were analyzed. 2) Alluvial soil containing ammonium sulfate or urea, was treated with each heavy metal at the levels of. 10, 100, and 1,000 ppm. After the soil was incubated at 30°C, the process of nitrification and ammo-nification was analyzed by determining the content of ammonium-N and nitrite+nitrate-N. The results obtained are summarized as follows: 1. The growth of Azotobacter and Fusarium was affected by chromate at the level 25 μm and Azotobacter was affected more than Fusarium. Chromium chloride also prevented the growth of Azotobacter at a level of 25 μm but only slightly that of Fusarium. Tungstate did not reduce the growth of Azotobacter at all but inhibited considerably the growth of Fusarium at a level of 5 μm. These phenomena were considered to be caused by the inhibitory effect of tungstate on the nitrate reductase activity of Fusarium.2. Nitrification was prevented at the 10 ppm level for chromate and at the 1,000 ppm level for chromium chloride. Vanadate also affected nitrification at the 1,000 ppm level.3. Ammonification was not affected as significantly as nitrification, but chromate reduced it at the 100 ppm level while chromium chloride affected it slightly at the 1,000 ppm level.