3 What is irrigation?
Irrigation6 replaces water, the essential ingredient of life, lost by the biophysical processes of plant growth and evaporation. It therefore supplements and augments rainfall to remove or reduce the influence of climatic variability on the lands’ productive capacity. Figure 1 illustrates the concept of extra pasture production from irrigation.
Fig. 1 Stylised pasture production profile
Note that rain is natural irrigation and can have similar effects but in a less controlled and predictable way. The more variable or low the rainfall in a particular region, the more valuable irrigation is likely to be, on suitably contoured land, in supporting a particular land use or combination of land uses in that location. The relative value can change over time with climate, market requirements, costs and technology.
The management of the water and the use to which it is put will determine its value (or otherwise). This implies that anywhere can benefit from irrigation to provide certainty about water. The question of whether it has a positive or negative net value is an economic one and a function of investment, time, consistency, risk, value of the product and natural rainfall quantity and patterns e.g., Waikato vs Canterbury. Most production systems can be undertaken without irrigation, but such is the variation and risk in the system that some particular land uses in some particular locations would be financially non-viable without it. By guaranteeing the availability of one of the variable productive resources the irrigator is able to optimise the utilisation of other fixed and variable factors of production (land, labour and capital).
There are also intangible or indirect impacts, such as peace of mind, increased land values, increased owner labour, increased scale of the production unit, and off-farm impacts such as population redistribution, employment creation, environmental impacts, demand for services and investment in processing plants.
6 Irrigation is “the artificial augmentation of the amount of water available to crops [or pasture], either by spraying water directly on to the plants or making it available to their root systems through a series of surface channels or ditches”. Source - A Dictionary of Ecology. Ed. Michael Allaby. Oxford University Press, 1998. Oxford Reference Online. Oxford University Press. www.oxfordreference.com/views/
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