EXPERIMENT WITH TREE FERTILISERS

Press, Volume C, Issue 29621, 18 September 1961, Page 3

EXPERIMENT WITH TREE FERTILISERS

Silt 6in deep laid down.in a struggling pine forest at Yaldhurst four years ago has resulted in a much improved growth, and the Soil Survey office is trying to find out why. It could be that where forests have not done well on stony Canterbury soils, the cause may be not so much water shortage, as generally believed, as a scarcity of certain nutrients. The silt was laid down during the 1957 Waimakariri flood in about five acres of a 30-year-old forest of some hundreds of acres of Pinus radiata, owned by the North Canterbury Catchment Board. The forest is mostly on almost bare gravel, with patches of sand; silt does not usually deposit beside this stretch of the river because of the swiftness of flow. (The 1957 deposition was caused by a cross stopbank). On the gravels, the trees have been growing very poorly, some of them being only an inch or two in diameter. Most have short and yellowish needles. About a year after the flood, the trees affected began to lengthen their needles and take on a greener hue, and their roots proliferated. Probably they also increased in girth, although this cannot be proved, since no previous measurements had been taken.

The improvement was noticed by Mr J. E. Cox, of the Soil Survey office, who brought it to the notice of the catchment board and the Forest Research Institute. The institute analysed samples of the needles and found they contained more than 50 per cent, more nitrogen than needles from neighbouring trees unaffected by the silt, as well as a little more potash and more than 100 per cent, more copper.

The implication that copper may be important to the nourishment of .adult trees is a new one, as no observed response to the element has been recorded except in plant nurseries in England, where mortality was reduced and tip-bum overcome by copper fertilisers. It was decided that the institute’s findings should be followed up by fertilising some of the unaffected trees with nitrogen, potash, and copper, the catchment board providing the fertiliser while the Soil Survey office does the field work.

Fourteen plots, each of onetenth of an acre, with tree growth and soils as nearly as

possible comparable, were selected for the experiment. Measurement at breast height of the diameters of the trees on the plots was completed yesterday, and on Monday the fertilising will start. The plots are in two groups of seven, each plot in the second group being given identical treatment with the corresponding plot in the first group to provide a standby in case of accident. The seventh plot of each group will be left completely untreated, as a “control;” The experiment is expected to last about two to three years.