Abstract:
Many regions around the world have farms surrounding potentially active volcanoes that have been dormant for decades to centuries. In New Zealand, dairy farming is one of the most important contributors to the economy and many farms are exposed to the hazard of heavy tephra fall from surrounding volcanoes. However, without any recent experience, a new major eruption and tephra fall would be an unfamiliar soil and pasture remediation challenge for New Zealand farmers. The overall aim of this research is to use a mixed-methods approach to identify suitable and effective remediation strategies for pastoral systems in the volcanic North Island of New Zealand (and by comparison agricultural systems elsewhere) following large-scale tephra deposition. Twenty-three farmers from the North Island were interviewed in order to gain insight into the current understanding of tephra fall risk and associated production recovery strategies needed for the pastoral agricultural sector. Of the interviewees, 26% had experienced past minor tephra falls on their farms, and 70% believed they were at risk of experiencing tephra fall. Around half of all interviewed farmers (48%), including one who had previously experienced tephra fall, provided suggestions for possible remediation techniques. The remaining half (52%) did not know what to do if tephra were to fall on their farm. The farmer-suggested remediation strategies are: i) waiting for rainfall to wash away the tephra (for thin falls); ii) cultivation; iii) re-grassing; iv) ploughing; v) using fertilizers; vi) flipping the upper 0.5 m of tephra/soil; and vii) physical removal. Based on these suggestions from farmers, together with a thorough literature review, seven simple remediation strategies were tested under the simulation of heavy (20 and 30 cm thick) tephra fall in field and pot trials. The field trials were set-up on working dairy farms in Hamilton and Taranaki, and the pot trials were carried out in Auckland. The following remediation strategies were tested over a period of 11 months: i) no treatment, ii) adding cowshed effluent, iii) adding fertilizer mix, iv) ploughing or mixing, v) flipping, vi) liming, and vii) applying alternative plant mix. The aim was to measure yields as well as herbage and soil chemistry to determine the most effective and efficient remediation strategy. Applying cowshed effluent gave the highest yield for both rhyolitic and basaltic tephra in field as well as pot trials. Flipping was an effective strategy at one of the two field trial sites. Applying fertilizer led to slow but promising yield increases. None of the remediation strategies led to soil nutrients of the affected soils returning to topsoil compositions, however they showed better nutrient levels than untreated soils. Planning the implementation of remediation strategies to sow seeds in a suitable season (to support germination and growth) as well as monitoring and controlling weed growth were revealed to be important aspects of any remediation. The costs of the individual remediation strategies were then evaluated against their yields to identify the most cost-beneficial strategy. This revealed that applying cowshed effluent was both the highest yield producing and least expensive recovery technique. However, whatever the remediation strategy used, the costs of any farm-wide pasture remediation are likely to be difficult to meet for any individual farmer. Hence, in the absence of major external stimulus packages, remediation is likely to take place more gradually, with parts of the farm being brought back into production as income becomes available. A key barrier to effective recovery is lack of rapid access to appropriate knowledge during and following a tephra fall. It is hoped that the results of this study will provide a key reference amongst the farming community when considering farm system preparedness for (and recovery from) tephra fall.