NITRIFICATION IN DUTCH HEATHLAND SOILS .2. CHARACTERISTICS OF NITRATE PRODUCTION

Some characteristics of nitrification in 41 humus samples of Dutch heathlands were studied. Most of the acid humus samples (30) showed accumulation of nitrate during a 4-week incubation of field-moist material. In these samples net nitrate production was completely blocked by 0.06% acetylene indicating that nitrification was probably of a chemolithotrophic nature. From a comparison of the net production of nitrate in humus suspensions at pH 4 and pH 6 a differentiation into four patterns could be made: I. No nitrate production at either pH value studied (12 samples) II. Acid-sensitive nitrate production (3 samples) III. Acid-tolerant, pH-dependent nitrate production (10 samples) IV. Acid-tolerant, pH-independent nitrate production (16 samples) The results show that acid-tolerant, chemolithotrophic nitrification is widespread among Dutch heathland soils. Absence of potential net nitrate production in humus samples is most likely caused by limitations in the supply of ammonium or oxygen. © 1990 Kluwer Academic Publishers.