Humic acid relieves pH-inhibition of nitrification in continuous-flow columns

Abstract

Humic acids obtained from a commercial source and isolated from mushroom wheatstraw compost inhibited nitrification by Nitrosomonas europea and Nitrobacter agilis in a continuous‐flow column at concentrations in excess of 100 μg cm−3. Lowering the pH of the input medium also reduced the rate of nitrification but in the presence of the compost, and to a lesser extent the commercial humic acid, pH‐inhibition was relieved. With the commercial humic acid, this effect can be explained in terms of the buffering capacity of the extract.