Skip to main content

Farming and Agriculture

Heaven sent conditioner from Taupo eruption

Malcolm has been farming for 70 years in Hauraki in the Coromandel Peninsula. He writes this week about the remarkable deposits of material from the Taupo eruption.
 |  Malcolm Campbell  | 

We have established that a great blanket of mineralised soil arrived over the land we later farmed. This soil was identified as coming from the Taupo Eruption 1800 years ago and had been thrown or blown over 150km.

An estimation puts the weight of soil at 1.3 to 1.7 tonnes per cubic metre. Taking 1.5 tonnes per cubic metre as an average, and in the compacted state on our property, this layer at 200 mm deep, every 5 square metres had 1.5 tonnes deposited on it. These are mind-bending figures because one hectare at 10,000 square metres received 2,000 tonnes. Our farm of two hundred hectares was deluged by 400,000 tonnes. When this material descended it is unknown at this stage whether it was wet or dry or dusty and loose. Obviously, it has compacted and become wet and this is the basis for the above calculations. So, what is important about all of this?

Initially this layer was below our acid topsoil, but later with deep cultivation it became mixed with the peat soil and the results were magical. Where mixing had taken place, the difference was starkly obvious. The pasture was stronger, much more resilient to dry periods, had a denser sward and the cattle and maize crops just loved it all. However, in the early stages of land development, we had sought advice from Department of Agriculture Officers and although the changes were pointed out to these people, none seemed the slightest bit interested. Most just shrugged their shoulders and said, “Oh, it is just one of those things.”

Up and until then, we had no idea what this gritty brown material was and the answer was not revealed until around 1970 – 74 when identified by Waikato University. Subsequently, samples of this material were sent to CRL Energy Laboratories in Wellington for detailed analysis. Remember we are in the middle of developing a peat swamp devoid of any fertility and here nature and violent nature at that, has delivered the following. Fe2O2 IRON 0.61%, MnO MANGANESE 0.07%, TiO2TITANIUM 0.27%, CaO CALCIUM 0.26%, K3O POTASH 3.4%, P2O3 PHOSPHORUS 0.06 %, Al2O3 ALUMINIUM 10.42%, MgO MAGNESIUM 0.04%, Na2 O SODIUM 4.11%, and a high content of SiO2SILICA 55.44%. These percentages are on a weight basis of the dried material, obviously much lighter than the water-soaked material. Fancy finding titanium in a peat swamp. Titanium is combined with steel to improve the strength and add resistance to corrosion. Surprising and yet not surprising is the high level of silica. Silica is the most prevalent mineral on earth. However, it comes in different forms and some forms are beneficial for soils and some are not beneficial to the soil. Everybody is familiar with the seashore and beach sand (silica as silicon dioxide) that we turn into sandcastles and so on. However, it is not beneficial to pasture growth. As a result of what had been learned, a natural hydrated silica was spread on selected areas of the Waihi farm on 24 December, 2016 and a sketch map of where it was spread was drawn. It was a good summer with good summer rainfalls and by mid-February 2017, about six weeks after spreading, a response to the silica could be observed visually. And the improvement of the pasture has continued, with visitors able to see the results of the initial trial plots. With such positive evidence the rest of the property has been spread with silica-based conditioner.