Possibility of nitrification suppression by a tropical grass - the effect on multiplication of ammonium-oxidizing bacteria and nitrous oxide efflux

摘要

The effect of Brachiaria decumbens, B. humidicola and Melinis minutiflora on nitrification in soils was examined. These three grasses were grown in pots filled with loamy Andisol for 2 weeks and then ammonium-N was applied to the soil as ammonium sulfate. After ammonium-N applications, the number of ammonium-oxidizing bacteria in soils increased more than ten times for two grasses compared with B. humidicola. In the case of B. humidicola, the number of ammonium-oxidizing bacteria maintained the same value for 27 days. Three grasses were grown in 1/5000 a Wagner pots for 4 weeks and then ammonium-N was applied to the soils for the determination of nitrous oxide emissions. From one day after the applications of ammonium-N, emission of nitrous oxidefrom the soils in which B. decumbens and M. minutiflora were grown was observed and continued more than 4 days. However, there was little emission of nitrous oxide from the soil in which B. humidicola was grown. Moreover, after determination of nitrousoxide emissions, plant roots were removed from the soil and ammonium-N was reapplied to the soils. Only in the soil in which B. humidicola was grown, was nitrification delayed. From these data, it seems likely that B. humidicola inhibits nitrification insoil; in particular, it suppresses the multiplication of ammonium-oxidizing bacteria in the soil as well as the emission of nitrous oxide to the atmosphere.