The first major survey of the extent and severity of erosion in the South Island high country was carried out by J. D. Raeside and H. S. Gibbs in 1945.
They found that 25% of the land was extremely eroded, with less than half the topsoil remaining. Only 20% had minor or no erosion.
The first national erosion survey was made in 1973 as part of the New Zealand Land Resource Inventory.
Farmer versus government
The call for quantitative measurements was, in part, the result of debate between farmers and regulatory bodies about the impact of farming methods on soil erosion. A royal commission on sheep farming, which finally reported in 1949, saw farmers in deep conflict with conservationists over the use of private land.
Aerial topdressing (applying fertiliser from small planes) was first trialled in 1949. The main aim was to restore the fertility of hill soils, establishing a vigorous pasture cover to reduce erosion. By this method, superphosphate and white clover could be spread onto relatively unproductive land. This resulted in the widespread pastoral development of hill country.
The increase in pasture cover led to a reduction in sheet erosion and associated gully erosion.
Never too late
Surface erosion can reduce up to 60% of crop yield, 80% of pasture growth and 90% of tussock biomass. Most of these losses can be stopped with soil conservation methods.
Catchment board research
Catchment boards, which managed river catchment areas, undertook research and demonstration projects on local erosion. The South Island focus was mainly on managing high-country tussock land. In the North Island, researchers developed ways to control gully erosion and slips.
Soil conservation farms
With the strong advocacy of soil conservator Doug Campbell, the Soil Conservation and Rivers Control Council purchased or leased a total of 24 farms or areas with erosion problems. These ranged from Wairākei in the North Island’s central plateau, to Tangōio near Napier, Makara near Wellington, Wither Hills near Blenheim, Moutere near Nelson, Adair near Timaru, Tara Hills near Ōmarama, and Mid-Dome in Southland.
These farms were run by the Department of Agriculture with the aim of researching and demonstrating erosion control measures appropriate to each region. All the farms were later sold.
Forest Service research
In 1956 the government Forest Service established the Forest and Range Experimental Station in the Craigieburn Range. Researchers investigated the land at high altitudes (above 1,000–1,200 metres) in problem areas. This was challenging work in a harsh climate. Research focused on understanding erosion processes and finding plant species to colonise and stabilise steep, eroded slopes.
As a result of the Water and Soil Conservation Act 1967, soil conservation work moved from the Department of Agriculture to the newly created Ministry of Works Water and Soil Division.
The Soil Conservation Centre was set up at Aokautere near Palmerston North, and investigated the impact of soil erosion on pasture productivity in the East Coast, and on Taranaki hill country. Research included testing poplar and willow species for controlling gully and slip erosion, and using remote sensing – such as satellite imaging and aerial photography – to assess the effects of erosion on the landscape.
In 1986 the Ministry of Works was disbanded. Soil erosion research is now carried out by Crown research institutes – principally Landcare, but also HortResearch, AgResearch, the National Institute of Water and Atmospheric Research (NIWA), and Scion.
Detailed assessments (at a scale of 1:63,000) were not conducted until the 1970s. In 1999 they were completed at a scale of 1:50,000. The extent and severity of the erosion problem is given in the Ministry for the Environment’s 1997 assessment of the environment.
Modern techniques such as remote sensing and geographical information systems (GIS) can be used to rapidly evaluate the degree, extent and type of erosion.