SOIL EROSION

Otago Daily Times, Issue 26637, 6 December 1947, Page 8

SOIL EROSION

ATTENTION MERITED NORTH ISLAND SURVEY AREAS NOT EXTENSIVE P.A. WELLINGTON, Dec. 5. A synopsis of the soil erosion survey of the North Island, recently completed by the Department of Scientific and Industrial Research, was presented by Mr L. I. Grange in evidence before the Royal Commission on sheep farming. Three main types of soil loss were recognised, he said, those caused by slipping, wind, or sheet erosion. The total of the North Island area of soils that slipped or were liable to slip was 9,363,000 acres of which 6,163,000 acres were potentially rapid deterioration areas. The lattfer were found in hard sandstone country from Wanganui north to Awakino Valley, on shattered shales to the west and north of Gisborne, in coastal Wairarapa, and on unconsolidated sands between Napier and Te Pohue. They occurred also in relatively small regions that had been cleared of forest and where rock screes were common small slips formed near the top of the slopes, exposing the rock, which fretted away and gradually formed a long scree of rock fragments down the slopes. Such soils were common on the very steep slopes of the Rimutaka, Tararua, Ruahine, and Raukamara Ranges. Wind erosion accounted for the potential deterioration of 4,557,000 acres, of which the major part was found on flgt and rolling land where the soil was friable, brown, and volcanic. Sheet erosion, the gradual removal of top soil by running water, took place on open scrub land and on open pastures. The total area of soils on which it was ccurring or liable to occur was 1,324,000 acres. It would be seen, said Mr Grange, that while in the North Island soil erosion was not alarming, even on hilly and step soils that were being grazed, there were several areas that merited attention and same urgent action. The better class of slipping soils (2,937.000 acres in grass and scrub) would continue to be grazed, but it was important that a lessening of the soil loss should be aimed at. Investigation of the badly-slipping class of soils (3,083,000 acres in grass and scrub) was needed to give guidance on their utilisation. Where grazing was feasible, remedial measures should be adopted wherever possible. Wind erosion on hilly pumice soils (657,000 acres in scrub and grass) would need watching if development took place and methods were employed to obtain quickly a close pasture sward. ‘Wind erosion on high altitude pumice soils (557,000 acres mscrub and tussock), though serious, affected the sheep industry only to a very small extent. Sheet erosion on some very infertile soils (928,000 acres in grass and scrub) was serious, and it was necessary to find out the kinds of grasses that would best prevent erosion and the amount of fertiliser required to obtain an adequate cover with such grasses. ' With the present methods of farming continued agricultural utilisation of this country, located, mainly in the Coromandel Peninsula, the Norm Auckland Peninsula, the Great Barrier Island, and to the west of the Firth of Thames was in doubt.