Heterotrophic Nitrification - Effects of N-Serve on Ammonia Oxidation and Nitrification in Acid Soils of the Nilgiris

Nitrification process in the acid soils (pH 6.7, 5.6 and 4.3) of the Nilgiris was studied. Accumulation of nitrate was found to be higher in the soils with pH 6.7 and 5.6 than the soil with pH 4.3. Accruement of nitrite was observed along with nitrate only in the soil with pH 4.3 after 42 days of incubation. Addition of N-Serve, an inhibitor of autotrophic ammonium oxidizers and chlorate, (an inhibitor of nitrite oxidizers) completely inhibited the nitrate and nitrite formation in the soils of pH 5.6 and 6.7, but only 50% reduction in the formation of nitrite and nitrate was observed in the soil of pH 4.3. Nine heterotrophic organisms isolated from the soil with pH 4.3 were tested for their heterotrophic nitrifying ability in glucose peptone liquid medium. Among nine, two fungal isolates identified as Fusarium sp. and Penicillium sp. were found to produce significant quantities of nitrite and nitrate. The amount of nitrite and nitrate production by these fungi varied with different cultural conditions viz., nitrogen sources and pH.