In common with most newly developed countries, New Zealand has not escaped the consequences of rapid exploitation and waste of its forest resources and the conversion to farmland of its well-vegetated landscapes. This transformation of forest cover, with allied grass, fern, shrub, and swamp lands, into a wide expanse of grass brought problems in districts where some of the following conditions existed – high and intense rainfall, strong winds, and severe frosts at higher altitudes; young oversteep slopes, mountainous and hilly terrain; steep slopes; highly fractured rotten rocks; earthquake shattered zones; and steep active rivers, or erosive soils. The result of this transformation was an increased runoff which accelerated soil erosion (by sheet, slip, flow, and gully erosion) to such an alarming extent that legislation was necessary to bring about a control programme.
In 1941, as a result of comprehensive legislation, the Soil Conservation and Rivers Control Council was established. The wide powers of this Act made mandatory the promotion of soil conservation, mitigation of soil erosion, the control of flooding, and the use of land to achieve these objectives. Provision was made for establishing catchment boards and catchment commissions for organising and operating soil conservation, river control, and requisite drainage works in a district comprising one or more catchments with a community of interest.
Ten typical farms were acquired on problem hill country for the purpose of developing erosion control methods and suitable conservation farming practices for the types of problems in the country. Special conservation techniques such as pasture furrows, graded banks, broad base terraces, grassed waterways, discharge regulating dams, dams for stock water, gully control structures, and the use of trees for various purposes were gradually evolved to meet practical conditions. These methods of erosion control were then combined with good farming practices such as fire and pest control, spelling to encourage natural seeding and regeneration, top-dressing and oversowing, contour cultivation, and crop rotations, together with the use of cattle and fencing to modify and control grazing management. The integration of these special conservation and management practices, adapted to suit the district, provided a sound basis for a conservation farming system.
This system had to be tailored to fit the land. In order to determine the kinds of land involved, conservation surveys were developed to evaluate the degree and extent of erosion, the capability of land for permanent production, and the conservation practices required on problem catchments. As scientific an evaluation as possible was made of the soil characteristics, erosiveness, slope, climate, geology, natural vegetation, and past management, and from such an inventory it became possible to classify the land into eight standard classes. These classes, four of which are suitable for cultivation, and four are not, provide a reliable index to the capacity of the land for permanent production.
With the assistance of vital information on the capacity of land for permanent production, together with the various conservation and management practices necessary to control erosion and flooding, it is now possible to demonstrate conservation farming on a planned-farm basis on the various experimental and cooperative demonstration farms run in conjunction with catchment boards. Experience on these farms has proved that conservation management not only controls erosion but also increases the carrying capacity considerably.
In many of the large catchments on hill and high country where erosion and run-off were most severe, there remained a further problem – that of phosphate deficiency. As long as topdressing had to be done by hand alone, no major development was possible to restore fertility, improve protective pasture cover, and increase production on millions of acres of hill country. It was against this background that proposals were drawn up, financed by the Soil Conservation Council, for the original aerial topdressing trials and large-scale demonstrations in 1947–49. These captured the imagination and enterprise both of farmers and of operators to the extent that over 5 million tons of phosphate have been distributed by aircraft, largely on hill country. This has been supported by oversowing of grasses and clovers, by weed spraying, fence dropping, and rabbit poisoning. Unfortunately this improvement of pasture, which lays the foundations of a conservation farming system, has forged ahead of the capacity of catchment boards to support it by the necessary supplementary conservation practices.
The effectiveness of pasture furrows, graded banks, terraces, grassed waterways, and flood control dams in controlling soil and water movement on arable lands encouraged the Council to provide machinery and technical services, and to plan and install these conservation aids on a demonstration basis where farmers needed them. This work is now carried on by four units controlled by the Department of Agriculture.
The extensive subsidised river control and drainage works undertaken by fourteen catchment boards and financed largely by the Soil Conservation and Rivers Control Council had to be supported by conservation works in the upper catchments. This has led to a scheme in which farmers are subsidised for conservation works – gully, slip, sheet, and scree erosion control, and dams for flood control – which also benefit lands lower in the catchment.
Single practices such as gully control, terracing, dams, tree planting for stability and windbreaks, fencing to control grazing, initial seeding and fertilising of eroded land, and sand dune stabilisation are subsidised. Experience on cooperative demonstration farms, run in conjunction with farmers, has proved that special soil conservation practices, supported by good farming practices, not only control soil erosion and flooding but also considerably increase production. Hence the rapidly growing trend is now towards integrated erosion control and conservation management schemes, embracing the entire farm unit (conservation farm plans). Some 300 of these are now in operation.
At Glenmark, near Waipara, North Canterbury, the combined effect of conservation farm plans, operating over an entire problem catchment, has demonstrated that soil erosion and flooding can be effectively controlled. The progression from single conservation practices to combined conservation and good farming has demonstrated the necessity for, and the advantages of, such group action by all farmers in problem catchments. Catchment boards are successfully promoting several such schemes on catchments up to 120,000 acres.
In addition to the board's administrative rate, any special rate for the community works required in the catchment control scheme must be agreed to by the farmer group, while the conservation works done on each farm are subsidised by the Council through the catchment board.
Owing to the far-reaching effects of erosion and flooding, the value to New Zealand of soil conservation and river control cannot be overemphasised. Equally important is the availability of technical information and service to farmers prepared to take action. Press publicity is therefore coupled with the publication of bulletins (16 to date) for general use, together with the production and screening of cine-films (10 have been produced to date for theatre circuits and 20 for use in schools and at farmers' meetings).
The activities of these local authorities, which have been constituted to implement the Act, now cover approximately 80 per cent of the country, with an engineering and conservation staff to handle specific and local problems.
by Douglas Archibald Campbell, M.AGR.SC., B.SC., Chief Soil Conservator, Ministry of Works.