Irrigation has always been vital to agriculture, but access to water, and ways to maximise its effectiveness, have changed over the years. Landcare Research soil scientist Dr Carolyn Hedley charts an irrigation evolution.
Water channels built into the Central Otago hills in the 1880s to sluice gold from sediment became the earliest irrigation channels in New Zealand when pastoral agriculture took over from gold mining later that century.
The water rights, issued to the miners as property rights, became invaluable assets to pastoral farmers, who used ‘wild-flood’ irrigation of pasture. This developed into slightly more controlled ‘border dyke’ irrigation; it was energy efficient, but was hardly an efficient use of water. Border dyke schemes originally provided an inch per week to farms, which worked pretty well, but as more farms joined the schemes this interval increased, making systems less efficient.
Over time, the Government acquired the property rights for the development of larger irrigation schemes. The earliest such scheme in New Zealand was the Rangitata Diversion Race, which opened in 1945. Irrigation water from this race was responsible for transforming a large part of mid-Canterbury into highly productive farmland. The scheme is still very much in use and a large channel takes water from the Rangitātā River 67 kilometres north to the Rakaia River, near Methven. After the Second World War, other schemes emerged in the Canterbury and Otago regions, the two driest regions in New Zealand, where most of New Zealand’s irrigated land occurs. Examples of these schemes are the Ashburton-Lyndhurst scheme, opened in 1945 and supplying 13,300 hectares, and the Mayfield-Hinds scheme, opened in 1948 and covering 35,400 hectares.
Further advances were made as bores were sunk into the deep gravels of the Canterbury Plains to reveal valuable groundwater resources to supplement surface water. The first deep bore was sunk at Pendarves in 1968. This heralded a period of rapid increase in irrigation development through the 1960s, and by 1970 the total area under government irrigation schemes was about 100,000 hectares. The irrigation supported wealth generation in the Canterbury region, although concerns about negative impacts on the environment were beginning to emerge.
From the 1980s, farmer demand rather than government schemes drove the expansion, and irrigated land increased markedly between 1999 and 2010, from approximately 600,000 ha to 1,000,000 ha.
The dairy boom which began in the 1990s was accompanied by large scale conversion of land not only in the Canterbury region but in many parts of New Zealand, and this profitable land use change was accompanied by the introduction of new sprinkler irrigation technology. Sprinklers enable much greater control of placement, amount and intensity of irrigation. For example, a fixed depth of water of just a few millimetres could now be accurately applied uniformly to many hectares of land by one sprinkler system.
Today in New Zealand, irrigation demands about 80 percent of consumptive allocated freshwaters, (excluding hydroelectricity), which is similar to the global average. Globally, irrigated agriculture produces 40 percent of the world’s food on 17 percent of land under production, making it 325 percent as productive as rain-fed agriculture – and vital to current food demands. Further technological advances are enabling greater automation and improved control. We now have variable rate modification of sprinkler systems providing individual sprinkler control, so that irrigation can be varied to different soil and crop types under one irrigator. In conjunction with these precision irrigation systems, soil mapping sensor technologies have been developed to produce high resolution soil moisture maps. This technology, pioneered by Landcare Research, uses wireless soil moisture sensor networks positioned into the field to continuously monitor soil moisture in management zones and update irrigation scheduling plans. They also aim to optimise water use efficiency, minimise runoff and reduce drainage losses and nutrient leaching.
Future advances in irrigation are likely to provide even greater precision, and greater automation. Sensor web enablement will increasingly be used to monitor and control irrigation systems. Advances are being made in ‘harvesting’ and storing winter rainfall in higher rainfall hill country, adjacent to seasonally dry lowlands, to supplement water supply during the summer months. Some satellites now carry soil moisture surveillance capabilities, although this technology will be limited by cloud cover in New Zealand, which ensures the on-going need for on-the-ground monitoring and farmer engagement in management decisions.
Technology is likely to provide increasingly ingenious and efficient irrigation options to farmers over time, and the challenge will be to meet farmer demands for smart irrigation in an increasingly water-constrained world.
This story originally appeared in Primary magazine. Click here to subscribe.
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