Root development in plantations of radiata pine in relation to site quality, fertilising and soil bulk density.  R.O. Squire, G.C. Marks and F.G. Craig.  November 1975.  17 pp. (unpubl.)

SUMMARY

A wet-sieving extraction technique for fine roots and mycorrhizae was used to study root development in eight year-old Pinus radiata plantations growing on sandy clay loam soils near Koetong in north-eastern Victoria. The objectives were to study root development on sites of high and low productivity, to examine factors which might be responsible for differences in root development between these sites and to assess the influence of these factors on site productivity.

The experimental material was from four pairs of 0.04 ha plots which covered a wide range of site productivity classes between burnt windrows. Roots were collected in soil core soil cores at 5.7 cm intervals to 22.8 cm in the soil profile. The roots were initially classified as mycorrhizal, or non-mycorrhizal and then further classified as fine or large according to root diameter. Mycorrhizal and non-mycorrhizal fine roots were classified into two groups, “active” and “moribund or dead”, depending upon colour and the condition of cortical cells.

On all plots, the “active” fine roots were found to be mainly in the surface 11.4 cm of soil but the high site-quality plots contained many more active fine roots in this part of the profile than plots of low site quality. Mycorrhizal frequency change little with soil depth, but like the active fine roots was greatest on the high site-quality plots.

Fertilisation increased basal-area growth substantially on the plots of low site quality and this was associated with a significant increase in root concentrations in the surface 11.4 cm of soil on these plots. Almost all of this increase was due to “active” fine roots. On the high site-quality plots there was little basal area response to fertilisation, and a significant increase in root concentration only at the 11.4-17.1 cm profile level, this being only partially due to additional fine root growth. Fertiliser significantly increased mycorrhizal frequency in the surface 5.7 cm of soil on the low site-quality plots, but a significant decrease occurred on the high site-quality plots.

Soil bulk density and root concentrations were found to be inversely related at some profile levels only; In the surface 5.7 cm of the low site-quality plots and in the 5.7-11.4 cm and 17.1-22.8 cm profile levels of the high site-quality plots. However, as soil near the surface of the high site-quality plots contained much higher root concentrations than surface soil of the same bulk density on the low site quality plots, it seems that factors other than bulk density had a more important influence on site-quality of the young radiata pine trees in this study. Evidently nutrient availability is one of these.

Also published:

Squire, R.O., Marks, G.C. and Craig, F.G. (1978)  Root development in a Pinus radiata D. Don plantation in relation to site index, fertilising and soil bulk density.  Aust. For. Res. 8: 103-14.