Little Plant Used To Stabilise Roadside Banks

Forest and Bird, Issue 186, 1 November 1972, Page 20

Little Plant Used To Stabilise Roadside Banks

THE stability of roadside banks in the Upper Buller Gorge, on State Highway 6 between Eight Mile Creek and Inangahua Junction, today owes much to a little plant, Lotus pedunculatus, which grows naturally in the area.

LANDscape officers of the Ministry of Works were faced with the planting of 20 acres of cut and fill banks after the highway had been realigned and widened. On the advice of Dr K. F. O’Connor, then of the Grasslands Division of the Department of Scientific and Industrial Research, at Lincoln, they chose Lotus pedunculatus as the plant to be sown on the banks. Lotus pedunculatus is a leguminous herb with clover-like leaves and an extensive root system which binds the easily eroded rocky soil exposed on the banks after the highway has been widened. Ecology Not Upset As it grows freely in the area, its introduction to the newly formed highway slopes means that the roadside ecology will not be upset, and as taller competing plants find their way naturally to the sites occupied by the lotus, it will gradually become recessive and finally die out. In the meantime it will have built up the nitrogen level in the soil through its root nodules. This nitrogen will then be available to other emerging plants. The first experimental sowings were carried out on fairly flat areas in 1967. After these results were evaluated, dry methods of broadcasting the seeds were tried on a large scale, but these were not completely successful, and a switch to a wet mixture was decided after the Inangahua earthquake of May 1968, in which a major sowing was lost. In the spring of 1971 a contractor using a hydro-seeder treated 20 acres of steep cuttings with a special mixture formulated for this situation. The lotus seed was mixed with bentonite, mulching agent and adhesive, in a large tank filled with water. To this was added fertiliser, containing nitrogen, phosphorus, and a trace element (molybdenum) plus lime.

Immediately before application rhizobia bacteria were added to the mixture for the purpose of inoculating the seed in preparation for germination; the young plants will use the bacteria for “fixing” nitrogen from the atmosphere and enriching the soil as a result of the process. Banks Covered Now, a year later, the banks are covered with the little herb, except for a few localised washouts, and lichens and mosses have crept in with some not-so-welcome patches of grass. Woody plants such as konini, kamahi, tutu, and beech seedlings, have also appeared in places, all by natural introduction. Landscape staff are confident that the newly seeded areas will develop to . a mature plant cover of the type in neighbouring areas and that a balanced ecological relationship will be built up. As the result of the success of the lotus, the landscapers are interested in trying it on similar banks in the Rahu Saddle and near the summit of the Lewis Pass bn the highway between Westport and Christchurch.

Book Review "Fiat Book of Common Birds in New Zealand"

A companion book has just been released for the “Fiat Book of New Zealand Trees”. It is on birds and illustrates 43 commonly seen birds both native and introduced. For each bird there are listed the field characteristics, the distribution and habitat, and breeding notes. The birds are all illustrated in colour. The authors are Janet Marshall, F. C. Kinsky, and C. J. R. Robertson.

A. H. and A. W. Reed. $1.75.