VOLCANIC SOILS

Rotorua Morning Post, Volume 1, Issue 8, 1 September 1931, Page 5

VOLCANIC SOILS

THEIR NATURE, PROPERTIES, AND UTILISATION. VALUE OF SCIENTIFIC . RESEARCH. A leeture dealing with volcanic soils of the central North Island districts and their agricultural utilisation was delivered by Mr. Ti Rigg before the Wellington Philosophieal Society, last week, and is of particular interest in the Rotorua district. Although it has been known for many years that large deposits of volcanic ejeetments cover enormous tracts of country in the RotoruaTaupo zone, it is only during the last year that a full realisation has been arrived at of the very widespread nature of volcanic deposits throughout the whole central North Island territory, Mr. Rigg stated. From the work that had been done in the^ course of the soil reconnaissance survey during the last twelve months, it had been ascertained that volcanic deposits covered the whole country from Kawhia Harbour and Mt. Egmont, on the west coast, to Tauranga and Whakatane, on the Bay of Plenty, and Napier, on the East Coast. In particular districts the ; ash covering had been rempved by erosion or by slumping, and on the river flats extensive resortment of ash from different sourees had taken place. Vast Eruption. Of /the volcanic deposits -whic|h were responsible for the soils of the central territories, the most extensive deposit was one that had come from a vast eruption near Lake Taupo. Material from this eruption, which apparently took place in comparatively reeent times, covered the whole country from Te Kuiti and Taumarunui, in the west, and extended almost as far as Napier, in the east. Waiouru, in the south, and Rotorua, in the north, marked the limits of well-defined deposition in the north and south. Eruptions from Mt. Egmont were responsible for the soil types covering a great part of Taranaki, extending almost as far as Ohakune, in the east, and probably as far as Ohura and the Mokau River, in the north. Between the Mokau River and Te Awamutu the principal soil covering was derived from ash from another source. This ash appeared to be much older than that from the eruptions of Mt. Egmont and from Taupo. The same ash in the district between Te Awamutu and Putaruru contributed largely to the soils of this district; but there -appeared to be a superfieial coating of ash from an unknown source which materially in- ' flueneed the eharacteristie properties of these soils. Rotorua District. Ash from vents in the Rotorua eentre covered large tracts of country between Rotorua and Tauranga and Whakatane. The eruption of Mt. Tarawera, in recent times, covered in its turn, earlier deposits from the Rotorua centre lying between Tapawera and Opotiki. Ash from J tht Ngauruhoe eruption covered a somewhat restricted area in the vicinity of the mountain and overlies the Taupo ash. Volcanic ash from Mt. Tongariro is almost entirely covered by ash from the last Taupo eruption; but a considerable area of soil between Waiouru and Taihape has been identified as ash from the Tongariro eruption. Striking Differerices. Examination of the different volcanic deposits had revealed striking differenees in the chemical and textural properties of the soils derived from them. Chemical analyses showed that ash from the Egmont, Tongariro, and Ngauruhoe eruptions was andesitic in origin, and is well-supplied with lime and other bases. The phosphoric eontent of ash from these eruptions was notably high. The chemical analyses suggested that the soils derived from the weathering of these ash deposits were of high potential fertility. The rhyolitic deposits of Taupo and the Rotorua centre compared with soils derived from the recent Egmont and Ngauruhoe deposits were low in lime and phosphoric acid. The ash coating in the Te Kuiti district probably was andesitic in origin, but great leaching of lime and other bases had taken place. Texture Changes. Although textural changes in the soil derived from any particular ash deposit oecurred in traversing the country from the eruptive vent to the limit of deposition, it was surprising how unif orm the texture was in particular localities from any one volcanic deposit. The texture, however, of soils derived from different deposits varied widely from loam to gravelly sands. Difficulties. The great chemical and textural changes which are associated with the volcanic deposits very clearly pointed to the desirability of very detailed laboratory examinations in order to determine more aecurately the distinctive properties of the volcanic soils. This was a matter of great importance to the development of agriculture in the volcanic territory, as farming experience already had shown that difficulties were frequently encountered in connection with the grazing of stock on established pastures. A particular type of stock ailment affeeting sheep in the country west of Te Kuiti in recent years had occasioned much concern to farmers in this district. Investigations carried out by Mr. B. C. Aston under the auspices of the Department of Scientific and Industrial Researeh had shown that the pastures contain low amounts of lime and phosphate. Treatment with mixtures of limt and superphosphate accompanied by close grazing of the pastures, had resulted in great improvement in stock health on eertain farms, and also had greatly improved the carrying eapacity of the land. Not Busk Sickness. The incidence of stock ailment in the country to the west of Te Kuiti must not be confused with bush-sick-ness, which had presented such great difficulties to the extension of agriculture in certain areas covered by Taupo and Rotorua rhyolitie deposits. Bush-siekness in its acute f orm had been noticeable in particular localities from the moment when the land was broken in. Generally, bush-siek-

ness diminished in severity under ordinary farm management. The reverse appears to be the case in connection with the "dopiness" affeeting sheep in the districts west of Te Kuiti. The long and careful work of Mr. B. C. Aston, of the Department of Agriculture, had shown that typical bush-sickness on volcanic soils was associated with soils of a somewhat coarse texture. As a result of pasture and soil analyses, a deficiency of iron in the feed of stock had been suggested as the cause of bush-sick-ness. It had been demonstrated that administration of iron drenches and the provision of "iron licks" effected a .cure or greatly reducecl the incidence of the ailment. Volcanic Effects. During the conduct of the present soil survey, the observations that had been made has shown that bush-sick-ness was very definitely associated with particular volcanic deposits, and was not common to all the soil types derived from ash deposits. The rhyoJitic ash from the Rotorua centre, covering the country north of this centre, to the Bay of Plenty, and the Taupo deposit of widespread distribution, were very definitely associated with bush-sickness. The ailment oecurred at such widely separated points as Mamaku, Ngaroma, and Kopaki, which are all located on the Taupo deposit. Nelson Investigations. Investigations conducted by the Cawthron Institute, at Glenhope, in the Nelson territory had shown that a similar form of stock ailment oecurred on certain granite soils. The administration of ferric ammonium citrate had given great improvement in the condition of sheep, clearly pointing to a close similarity to bushsickness in the volcanic soils of the North Island. In connecton with the development of volcanic soils, the whole area of country covered by the Taupo deposits must be regarded with some suspicion in view of the incidence of bush-sickness at at least three points widely separated. The success that had been obtained by the use of iron "licks" in combating this ailment, however, gave great hope for the eventual development of intensive agriculture "on large areas of the Taupo deposit. In selected localities in this sector the carrying capacity of pastures sown to English grasses and clovers and' top-dressed with superphosphates, had been notably high, and if the bogey of bush-sickness could be definitely removed there was little question that very large areas of the Taupo deposit could be suecessfully farmed. Good Prospects. Much partly developed . country oecurred between Te Awamutu and Putaruru, which should respond in a wonderful way if broken in and sown in pastures. Lime and phosphate treatment should result in the maintenanee of excellent pasbures and high carrying capacity of stock. In concluding his address Mr.\Rigg stated that although the Soil Division established by the Department of Scientific and Industrial Researeh had been in existence for only a little more than a year, very valuable information had been secured. The different volcanic deposits had been identified, the approximate limits of deposition had been ascertained, the combined work of geologists and chemists of the Department of Scientific and Industrial Researeh and of the Cawthron Institute already "had resulted in new f ormation of great value to farmers in the volcanic ter-, ritory. Mueh" further work, however, was required in order to enable the greatest use to be made of the great areas of unoccupied country which presented sucb. great possibilities for agriculture.