Interacting effects of grass competition, fertilising and cultivation on the early growth of Pinus radiata D. Don at Koetong.  R. O. Squire.  August 1976.  9 pp. (unpubl.)

SUMMARY

A potentially serious problem developed during the first rotation of Pinus radiata D. Don in the Koetong plantation in north-eastern Victoria. The problem was mainly one of slow early growth on sites between burnt windrows; growth on the windrows was good.

This study examines the interacting effects of grass competition, fertilisation and cultivation on early growth of P. radiata growing on sandy clay-loam soils on a typical between-windrow site at Koetong. Twelve treatments including grass removal, fertiliser, ploughing and ripping, individually and in combination, were examined using a randomised block design. Treatments were replicated three times in rectangular 0.027 ha plots.

Grass competition was found to be of primary importance. It restricted growth directly and, more importantly, severely limited the ability of trees to respond to favourable nutritional and soil physical conditions. It appeared that these effects were mainly due to competition for soil moisture. Except for small height increases due to cultivation and fertiliser combined during the first year after planting, significant increases due to cultivation and/or fertiliser were only obtained in the absence of grass competition; fertiliser responses were large and cultivation responses moderate. These responses were largely additive when the treatments were combined. In the second year after planting the basal area growth of plants on fertilised and cultivated sites was almost eight times that on untreated sites; with fertiliser giving twice the response of cultivation.

The findings have important implications. Firstly, failure to control grass competition may lead to irretrievable losses in growth, these increasing in absolute terms with increase in the natural growth potential of the site. Secondly, and more importantly, the ability of outplants free of grass competition to respond markedly to fertiliser and cultivation, in near additive fashion provides an opportunity to stimulate early growth to a degree which could lead to substantially enhanced site productivity.

Also published:

Squire, R.O. (1977)  Interacting effects of grass competition, fertilising and cultivation on the early growth of Pinus radiata D. Don.  Aust. For. Res. 7: 247-52.