Early irrigation methods
The earliest irrigation schemes in Central Otago used wild flooding, where water was diverted to flood paddocks. While initial costs were low, labour input was high, and water use was inefficient.
Before the mid-1940s the main method of irrigation was the border dyke system, where parallel, 12-metre-wide, shallow channels were constructed across a paddock, and water introduced from a head race. The sequence of watering was manually supervised and very labour intensive.
Automatic irrigation system technology was developed for border dyke irrigation at the Winchmore Irrigation Research Station in the 1950s and 1960s. This system allowed a farmer to set up a 17-day irrigation roster, and for the whole farm to be watered, paddock by paddock, by only one person.
More recently, the border dyke system has been improved through precision land levelling, introducing wider border widths and higher flows, and the use of electronic controllers to sequence the irrigation flows.
In the early 2000s most of the irrigated land in New Zealand used sprinkler systems. This is because most use groundwater, which cannot provide the flow rates needed for border dykes. Also, new sprinkler technologies reduced labour input, applied water more efficiently, allowed more land to be irrigated, and could correct soil moisture deficits each day. As a result, both crop and pasture yields are increased, compared with the same amount of irrigation water used in a border dyke system. However, sprinkler systems use more energy for pumping.
Orchard and vegetable irrigation
A reliable and effective irrigation system is an essential part of growing orchard and vegetable crops in the drier parts of New Zealand.
Developments in orchard and vegetable irrigation progressed from surface flooding and furrow systems, to drip irrigation and permanent sprinklers set within rows under trees. In the early 2000s sophisticated computer-controlled drip and micro-sprinkler systems, capable of applying plant nutrients with the irrigation water (fertigation), were increasingly used.
Irrigation scheduling and control technology
Soil moisture is measured to make sure that plants are only watered when they need it. Private contractors operate soil moisture and irrigation scheduling services. They measure soil moisture using devices including TDR (time domain reflectometry) instruments, which send a pulse between two probes inserted into the soil. The strength of the reflected pulse indicates how much moisture is in the soil.
While the use of soil moisture scheduling is increasing, in 2008 it was probably used on only about 20% of irrigated land. However, it may become mandatory in the future as environmental pressures increase.
Water use measurement
By 2013 it will be mandatory for all of the 9,000 people with resource consents to take water to measure their water use to an accuracy of 5%. This is to improve the monitoring of the efficiency of irrigation and reduce energy consumption.