The Canterbury Plains are formed by extensive terraces and large alluvial fans near the main rivers, with a backdrop of downlands and hills approaching the Southern Alps. As you move east from the mountains the annual water deficit increases from low to high, and minimum winter temperatures increase from cold to cool (-3–3°C). The older segments of the upper plains have a thicker covering of loess than the younger alluvial plains. Large areas of the lower plains and some of the stonier soils on the upper plains were once planted in wheat, barley, oats, brassicas and pasture. These areas have been converted to dairy farms with the aid of large irrigation units. Irrigation is more extensive in Canterbury than in any other region.
The undulating, loess-derived downlands are used for semi-intensive sheep and beef farming, and cropping. Tussock grasslands, with higher rainfall, are on the slopes and flats of intermontane basins along the eastern ridge of the Southern Alps. These have shallow, stony and very friable soils. On the flat areas, the soil breaks apart and becomes ‘fluffy’ if cultivated. A large area in the Mackenzie Country has such soil, which, with the aid of irrigation, can be used for dairying.
In the early 20th century the downlands irrigation scheme was set up to divert water from the Rangitātā River into large canals that crossed Canterbury’s upper plains. The water was accessed by farmers, who fed it into border-dyke channels in their paddocks. These were wide parallel strips with a low border of earth on each side, on a slight slope, which channelled the water slowly across the pasture. Today, land is irrigated by large sprinklers tapping underground water.
The main nutrients needed in Canterbury are phosphorus, sulfur and molybdenum. Deep, moist soils lie on easy slopes, and there are stony or eroded soils on steep slopes, where pasture growth is limited by dryness in summer and cold in winter and early spring. Oversowing the hills with inoculated clover seed, together with the application of molybdenum- and sulfur-fortified superphosphate, has been an inexpensive way to develop large areas of tussockland into pasture in all eastern areas of the South Island.
Central and North Otago
Central Otago is the driest region in New Zealand, with an annual rainfall of some 400 millimetres. Although it has fertile soils, pasture and crop growth is limited by the high (200–300-millimetre) annual water deficit. Minimum winter temperatures are very cold (less than 2.5°C). Many apricot and cherry orchards have been converted to vineyards. To the east, rainfall is higher and more uniformly distributed.
The predominantly rolling hill country in North Otago can have good pastures once the phosphorus, sulfur, molybdenum, and in some cases potassium, requirements are met. Where irrigation is available, large dairy farms are being established on flat or easy-sloping soils.
South Otago and Southland
In these regions the annual water deficit ranges from zero to low and the minimum winter temperatures from cold (-3–0°C) in the north, to cool (0–3°C) nearer the southern coast. The Southland Plains have over the last 10 years undergone a transformation in land use from predominantly sheep and beef farming and cropping, to dairying. The moist, brown soils generally require drainage, and are high producing under additional lime, phosphate, and sulfur fertiliser inputs. Pasture production levels are as high as in the Waikato. Molybdenum is also important on the loess-covered downland hill soils in the north and east, where sheep and beef cattle farming predominates.