Breaking in the Pumice Lands
One of the most mystifying agricultural problems in the first part of the 20th century was the wasting illness termed ‘bush sickness’ that affected sheep and cattle introduced onto recently converted tussock plains and shrublands on pumice parent materials in the centre of the North Island.
Scientists originally diagnosed the problem as a form of iron deficiency, and it took more than 20 years for the exact cause to be identified. This research pioneered the way for many future research projects investigating the relationship of animal metabolism to soil characteristics.
Before they were solved, these animal health problems had led to the conversion of the recently established pastoral farming on pumice soils (Fig. 1) to exotic forestry. Pinus radiata trees were planted into a large area, now known as the Kaingaroa Forest. This forest became the largest exotic forest in the world, with world-beating growth rates. The exotic forestry development was very successful, forming the basis of New Zealand’s future exotic timber industry.
Meanwhile, soil scientists were determined to discover the reasons for the ‘bush sickness’ problems. Soil surveys in the mid-1930s by Les Grange and Norman Taylor studied volcanic ash deposits and showed that bush sickness only occurred where tephras had been deposited during the Taupō and Kaharoa eruptions (about 200 AD and 1314 AD). Chemical analyses revealed that the sickness was caused by a deficiency in the trace element cobalt and that other trace elements, selenium and copper, were also deficient.
By the late 1930s the widespread use of cobaltised superphosphate had successfully controlled bush sickness and opened the way for successful pastoral development of these problem areas.