Story: Soils and regional land use
Page 6 – Northern and western South Island
Low annual rainfall, regular summer droughts (high to very high annual water deficits) and brown pastures are characteristic of Marlborough. Although minimum winter temperatures are cool (0–3°C), stone (summer) fruit and horticultural crops ripen well. Large areas of gravelly terrace soils have been planted in grapes, which are suited to the climate and are more productive than pastures.
Marlborough’s hill soils are similar to those in the Wairarapa and Canterbury, but in the dry climate they can develop underground ‘tunnel gullies’ that eventually collapse and erode. The loess-covered soils of the Marlborough Sounds receive more rainfall and are more productive, especially on south-facing slopes. Under original forest cover, and where rainfall exceeds 2,000 millimetres, some soils have become acidic and have low fertility.
New Zealand’s largest property is Molesworth Station, in the upper Awatere valley, Marlborough. In the mid-1900s it became over-grazed by sheep and rabbits, and was subsequently taken over by the government. By controlling the rabbits, removing the sheep and replacing them with cattle, the vegetation recovered and the property’s productivity improved. Molesworth is now run by the Department of Conservation, and is open to tourists in summer.
Sulfur-fortified superphosphate with added molybdenum is usually needed to establish pasture. However, large areas of the region, including what was once farmland, are protected nature reserves or have been planted in exotic forest.
Nelson and Golden Bay
This region has cool minimum temperatures of 0–3ºC in winter, and a low-to-moderate annual water deficit. Nelson is known for pip and stone (summer) fruit, berries, hops and kiwifruit, and its sunny climate. Horticulture is concentrated and expanding on the fertile Waimea and Motueka flats and terraces.
The very old Moutere gravels to the south and west form the basis of 100,000 hectares of hill-country soils. Molybdic superphosphate plus potash, as well as lime, copper and cobalt are necessary to establish pastures, which are mainly used for sheep and beef production. Large areas of these gravels are planted in exotic forest, especially in southern Nelson, where nitrogen, phosphorus and boron fertilisers are generally required. There are also significant areas of native forest.
Nearer the coast, on easier topography, the more weathered gravels support Nelson’s apple and pear orchards. These need magnesium and boron fertilisers. Golden Bay, on the western side of Tākaka Hill, has fertile alluvial flats, 90% of which is pasture and increasingly being developed for dairying.
The West Coast
The West Coast is a mosaic of alluvial soils on flat river plains, with native forest growing on river valley slopes. The area’s plentiful rain contributes to an annual water surplus. Minimum temperatures in winter are cool (0–3°C). A large proportion of New Zealand’s indigenous forest is on the West Coast.
Soils on the flats are either recently formed from flood gravels and silts, or are very old pakihi soils (a Māori word that means open country). Pakihi soils have developed perched water tables as a result of very compacted, impermeable subsoils or an iron ‘pan’. The recent soils can be cultivated relatively easily with some drainage and fertiliser, but the pakihi podzols need special attention. One approach has been to develop hump-and-hollow land, where a flat area is contoured to improve drainage. Exotic forestry uses this method, with trees planted on the humps. Dairy farmers have also made remarkable gains by ‘flipping’ their poorly drained soils. This involves the use of diggers to break open the impervious pans and mix the peaty topsoil with the sandy subsoil. By flipping and hump-and-hollow contouring, then fertilising and re-sowing pasture, cow stocking rates can be doubled and the renovation costs paid back within two years.
Establishing pasture in the West Coast requires lime and lots of superphosphate. Copper, magnesium, molybdenum, cobalt and potassium may also be needed. Dairying has expanded and intensified rapidly on all soils in recent years. Nitrogen and phosphorus, as well as some potassium fertilisers are needed for forest grown on pakihi soils. Forests on dredge tailings usually also need boron.