EFFECT OF THE INHIBITORS NITRAPYRIN AND SODIUM-CHLORATE ON NITRIFICATION AND N2O FORMATION IN AN ACID FOREST SOIL

An acid forest soil from beech forest gaps, which were either limed or unlimed, and the undisturbed forest was investigated for the type of nitrifying populations and the process of N2O evolution. To see whethe r nitrifiers were of heterotrophic or autotrophic origin, the nitrific ation inhibitors nitrapyrin and sodium chlorate were applied to distur bed soil samples which underwent laboratory incubations. Nitrapyrin in hibits autotrophic nitrification. In different studies, sodium chlorat e has been identified as an inhibitor either of autotrophic or of hete rotrophic nitrification. In the samples investigated only nitrapyrin i nhibited the autotrophic nitrification occurring in the limed soil. So dium chlorate effectively inhibited heterotrophic nitrification. In th e Limed forest floor samples, where most autotrophic nitrification occ ured, sodium chlorate showed no inhibitory effect. In another laborato ry incubation experiment, N2O evolution from undisturbed soil columns, to which the above inhibitors were applied, was investigated. In thos e samples, in which nitrification had been reduced, neither inhibitor significantly reduced N2O evolution. Thus it was concluded that the co ntribution of nitrification to N2O losses is negligible, and that N2O evolution arises from the activity of denitrifying organisms. Microbia l biomass and respiration measurements showed that the inhibitors did not affect microflora negatively.