South Auckland and Waikato
Topography and climate
The gently undulating topography of most of South Auckland and the central Waikato basin contains some of the most productive farmland in New Zealand. The minimum winter temperatures are 3–6°C, with warmest temperatures further inland. The annual water deficit is low, although summer droughts can occur.
Soils and land use
The free-draining loam soils have developed from volcanic ashes of varying ages, and are easily cultivated. They are good for crops, horticulture or intensive dairying. In the south of the region, where there is more rain, the soil contains a fine clay called allophane. This absorbs phosphate and sulfate, so extra fertiliser is often needed to establish good legume-based pastures.
In the Hamilton basin and towards Matamata, the Waikato River has sorted and deposited a mixture of ash material to form complexes of poorer drained gley soils and free-draining, sandy and gravelly soils prone to summer drying.
In the Hauraki Plains and around Hamilton there are large areas of peaty loam and peat soils, formed as a result of poor drainage. Most have been drained for dairying. All need a lot of added lime, which is ploughed in for best results. Heavy applications of phosphorus, potassium and sulfur are also initially needed, and boron must be added for brassica crops (such as cabbages and broccoli). Pastures and the animals who eat them may be copper deficient, and selenium deficiency is common in young stock.
The steeper hill country to the west is a mosaic of ash-derived soils on rolling and moderate slopes, and mudstone-derived soils on steep slopes where the ash has been washed off. Pastures on the steep slopes need less phosphorus and sulfur fertiliser than those on the ash soils, and respond to lime. Most pastures are used for sheep and beef farming. Shallow hill soils may need phosphorus fertiliser for exotic forestry production.
Steep slopes impose greater moisture stress on pastures because of the greater opportunity for runoff of rain water. On north-facing aspects there is greater evapo-transpiration of soil moisture than on flat land. As a result, pastures on hill slopes usually show browning earlier in summer than associated flats.
Coromandel and Bay of Plenty
This region is well known for its beaches, and is the main kiwifruit and avocado growing area in New Zealand. However, horticulture occupies only about 1% of the land area. About 90% of the area is covered by indigenous forest, exotic plantations or pasture. Dairying and horticulture are still expanding on the flat and gently rolling land at the expense of sheep and beef farming. The Coromandel ranges once grew kauri forests.
What’s in superphosphate?
About 2 million tonnes of superphosphate fertiliser are applied to farms in New Zealand each year. Superphosphate is made by adding sulfuric acid to rock phosphate. Superphosphate contains both sulfur from the sulfuric acid, and phosphorus from the rock. Other nutrients can be easily added where necessary.
Minimum temperatures in winter are higher than in central Waikato, and the annual water deficit is only slight or near zero.
The soils are mainly loams derived from volcanic ash, crumble easily and are free draining. They strongly retain phosphate and sulfate, so relatively large amounts of superphosphate fertiliser are needed. They are deficient in potassium and increasingly in cobalt. Lime is eventually required to counter the effect of soil acidification, which occurs naturally under grazed grass/legume pastures.