Nitrification activities of some New Zealand soils and the effect of some clay types on nitrification

Abstract

Short-term nitrification actIvitIes (SNA) and the numbers of nitrifying bacteria in nine :\ew Zealand soils were examined. All the soils contained significant numbers of nitrifyinx bacteria (in the range IOL107/g). Nitrification activities of different soils were widely different, but no relationship was observed between SNA and the numbers of nitrifyin~ bacteria. Separation of a high nitrifYing soil into various size fractions did not affect the short-term nitrification activity. Although pure cultures of Nitrosomonas sp. failed to nitrify below pH 6.2, a colloid fraction separated from an allophanic soil was capable of nitrification at pH 5.5. Similarly Nitrosomonas sp. grown in the presence of laboratory synthesised allophane was able to oxidise ammonium to nitrate at pH 5.5.

The variability of nitrifying activity in field soils

“…The nitrification process can also vary, both spatially and temporally, through variation in substrate inputs-this is particularly so under grazed pasture where excretal N provides markedly localized sources of NH 4 -N Ryden et al, 1984;Thompson and Coup, 1940). In this work we describe an attempt to quantify the effect of some of these factors on the nitrifying activity of a grazed pasture soil using the short-term nitrification assay (SNA) (Darrah et al, 1986;Sarathchandra, 1978) as an index of the size and activity of the soil nitrifier population at particular times. By this analysis, we hoped (a) to identify trends in the variation in nitrifier activity, and hence in soil NO~ supply, with season of the year and (b) to interpret these variations in terms of the measured effects of pH and moisture tension on the SNA value.…”

Effect of rate and form of dicyandiamide application on nitrate leaching and pasture production from a volcanic ash soil in the Waikato

“…Much of the dairying takes place on Allophanic soils derived from volcanic ash and these soils have high rates of nitrification (Sarathchandra 1978).…”

Nitrogen mineralisation and the activity and populations of microflora in a high producing yellow-brown loam under pasture

“…It is difficult to establish minor population changes using MPN method because of the low order of precision of this method (Alexander 1965). Numbers of ammonium oxidisers were generally low compared to numbers of nitrite oxidisers, as has been reported for IO New Zealand soils (Sarathchandra 1978). Fragments of mycelia as well as fungal spores, can pro-,duce colonies on agar plates (Menzies 1965).…”

“…However, liming did not significantly affect the numbers of ammonium and nitrite-oxidising bacteria (Table 4). These organisms, already in an active state at low pH (c:!.5.5) in volcanic ash soils (Sarathchandra 1978), may not be further stimulated by the addition of lime and their numbers may be limited by the availability of ammonium substrate, which is converted rapidly to N03-. (No accumulation ofNH4+ was noted in the present series of experiments involving lime.)…”