XVII. Nitrifying activities of two cultivated Soils

Summary

Nitrifying organisms occurred in the soils of two New Zealand tussock grasslands. The nitrifying activity of Taupo soil was less in the vicinity of the roots of Festuca tussock plants than in soil at a distance from these plants but little difference was found between the samples of Cass soil. These and previous results indicated that growing Festuca tussock plants do not stimulate the activity of nitrifying organisms in these tussock-grassland soils.

The nitrifying activity of the Taupo soil was generally greater in summer than in spring but no seasonal differences were found in the strongly acid Cass soil which had a low nitrifying potential.

In both soils, a significant increase in nitrifying activity resulted after growth of crops or introduced pastures, following preliminary ploughing and the addition of fertilisers. The activities of these cultivated tussock-grassland soils were similar to those of three other cultivated soils that were originally under forest.