Topography
Much of Northland is undulating to moderately steep hill country that has been weathered by the subtropical climate over a long period of time. As a result, most of the soils contain a lot of clay and are called clays or clay loams.
Climate
Northland has a subtropical climate, with minimum winter temperatures of 6–9°C. Grasses such as paspalum and kikuyu grow in pastures. Paspalum is found further south, but kikuyu cannot thrive where there are winter frosts.
Soils and land use
On the flatter areas, which were originally covered in kauri-dominated forest, so-called gumland soils developed. These were mined for kauri gum in the late 19th and early 20th centuries. Superphosphate is needed on gumland soils used for forestry, and potassium fertiliser is used on podzolised sands (areas leached of nutrients by weathering and acid tree litter). Forest grown near coastal sand dunes also need nitrogen fertiliser, or associated plantings of lupins – which ‘fix’ nitrogen in the soil so it can be used by the trees.
Gley podzol soils are used for sheep and beef farming, and dairying, but need lots of initial fertilisation. Derived from sedimentary parent rocks, gley podzols have brown clay topsoils, and are wet in winter and spring. They cannot support large numbers of cattle at those times, unless the soil is well drained.
The other Northland soils are mostly a mix of brown soils, free-draining soils from basalt, and poorly drained hill and steepland soils from old andesitic volcanic action. The best free-draining (oxidic) soils, from more recent basaltic volcanism, are used for dairying and a range of horticultural crops.
All Northland’s soils are acidic and low in natural phosphorus and sulfur, so lime and superphosphate fertiliser (9% phosphorus, 11% sulfur) are needed for pasture growth. Other nutrients such as potassium, molybdenum and copper may also be required, especially after the land has been farmed for some time.
