The effect on nitrogen availability of adding fragmented wood to the soil

Abstract

Changes in nitrate content of incubated sawdust-soil mixtures were followed in order to investigate the effect of wood species, extraction of the sawdust, soil texture, addition of limestone, and form of nitrogen added on the time trend of nitrogen uptake and release. Wood species had the greatest effect on the maximum amount of nitrogen taken up. For mountain ash (Eucalyptus regnans F. Muell.), red ironbark (Eucalyptus sideroxylon A. Cunn.), and radiata pine (Pinus radiata D. Don), the average maximum amounts of nitrogen taken up were respectively 1.6, 1.4, and 1.0 per cent. of the oven-dry wood present. It is suggested that these amounts are inversely related to the degree of lignification of the wood. Maximum uptake was reached in a period varying from 5 weeks (mountain ash) to 11 weeks (other species), which suggested that under temperate conditions in the field nitrogen additions should be spread over a period of 6-12 months or more to avoid losses. Addition of calcium carbonato caused increases in the rate of nitrogen uptake and the maximum value reached. When a nitrogen salt only was supplied, there was evidence of deficiency of some other element. The other factors investigated had little or no effect on nitrogen uptake. Nitrogen was released very slowly, which indicated that under temperate conditions in the field the rate of release would be too slow to be useful for many crops. Because of the slow rate of release, it is expected that the experimental results for maximum uptake would apply to field conditions favouring a reasonable rate of decay. Mycological examination revealed mainly Ascomycetes and Fungi Imperfecti, no Basidiomycetes being observed.