Story: Irrigation and drainage
Too much water or not enough water can both cause problems for farming. In drier areas of New Zealand irrigation schemes have made farmland lush and productive, while drainage of waterlogged land has made it possible to grow crops and pasture. However, both irrigation and drainage can have negative environmental consequences.
Full story by Terry Heiler
Main image: Moving spray irrigator
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Crops and pasture (grass for animals) need enough water to grow well. However, if the ground is too wet, they also cannot grow well. Farmers irrigate (water) plants when they are dry, and drain paddocks that are waterlogged.
Types of irrigation
In the 19th century farmers irrigated their land by diverting water from a river or stream to flood their paddocks. This was a lot of work, and didn’t water the ground evenly.
The border dyke system uses lots of channels to take water to paddocks. These were popular in the early 20th century, but most farmers have moved to spray and sprinkler irrigation systems.
There are many systems that spray water on crops or paddocks. The most popular is a centre pivot sprinkler system, which has an arm up to 800 metres long, and waters in a large circle. Spray systems use water more efficiently than flooding or border dykes.
Both border dyke and sprinkler systems can now be controlled electronically.
In the first half of the 20th century the government built channels to divert water from rivers to farms, and dams to store the water. These were mainly in Otago and Canterbury.
In 1946 the Department of Agriculture set up the Winchmore Irrigation Research Station.
Environmental issues with irrigation
As more land is irrigated, there are concerns that it is taking too much water from rivers and aquifers (underground water). Also, excess runoff water from irrigation can wash fertiliser and animal effluent into rivers and streams and pollute them.
There are laws that aim to protect the environment, such as the Resource Management Act 1991, and some rivers are protected by special orders. Farmers must have permission to take water for irrigation, and in the future they will probably have to report on the water they use.
Farmers drain water from boggy fields so that crops or grass will grow better. They sometimes dig ditches or shape the soil into humps and hollows. Another method is to use little tunnels or pipes under the ground to drain the water away.
Environmental issues with drainage
In the past, boggy land was often drained so it could be used for farming, but now people realise that wetlands are important habitats for native plants and animals. Also, the water that is drained from paddocks can pollute rivers and streams with fertiliser and animal effluent.