New Zealand Journal of Agricultural Research abstracts

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Impact of Ruapehu ash fall on soil and pasture nutrient status 1. October 1995 eruptions

SHANE J. CRONIN
M. J. HEDLEY

Department of Soil Science
Massey University
Palmerston North, New Zealand

R. G. SMITH

Ravensdown Fertiliser Co-operative Ltd
P. O. Box 448
Feilding, New Zealand

V. E. NEALL

Department of Soil Science

Massey University

Palnerston North, New Zealand

Abstract  Eruptions from Ruapehu volcano on 11 and 14 October 1995 covered large portions of the central and eastern North Island, New Zealand, with tephra, including c. 17 000 km² of land in primary production. The thickness and distribution of the tephra was mapped and it was chemically characterised in order to predict its effects on soil fertility. Tephra from the two eruptions contained 3.0 and 0.7 % by weight sulphur (S), respectively, 67-55 % of which was in an elemental form (S⁰), with the remainder in the form of soluble sulphate. The S⁰ in the tephras was derived from the former, hydrothermal Crater Lake system in the active vent of Ruapehu. Sulphate was derived from Crater Lake water and gases erupted with the tephra. Field and glasshouse investigations showed that the tephra significantly raised soil sulphate levels. The initial elemental S component was very fine grained (65-99% <125 um diameter) and oxidised rapidly causing depression of soil pH. In a transect of northern Rangitikei soil and pasture samples, S concentrations increased with increasing tephra thickness and remained above normal levels for at least 8 months after tephra fall. Pasture Se concentrations also rose briefly but returned to more normal levels for these soils after 5 months. Other nutrient elements were deposited in useful amounts only under heavy tephra falls. Toxic elements were minor components of the tephra sampled. As Crater Lake reforms following eruption episodes, future tephra eruptions from Ruapehu can be expected to have similar agronomic effects.

Keywords  Ruapehu volcano; tephra; soil fertility; hydrothermal Crater Lake; elemental S; Se; impact on pastures

New Zealand Journal of Agricultural Research, 1997, Vol. 40: 383-395

0028-8233/97/4003-0383 $7.00/0 (c) The Royal Society of New Zealand 1997

PDF file of entire paper: medium quality (1069K); (scanned from paper original: notes about this process)

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