Thursday, 03 May 2018 10:55

Irrigation not an environmental irritation

Written by  Jacqueline Rowarth
Jacqueline Rowarth. Jacqueline Rowarth.

OPINION: Irrigation can reduce soil erosion.

Of course, the irrigation has to be carefully managed and precision technologies are part of the management. However, there is no doubt that overcoming any drought period during warm temperatures allows increased pasture growth, which is associated with maintenance or an increase in organic matter, which in turn decreases the likelihood of erosion.

Any increased income resulting from the harvesting of extra pasture or crop can be invested in more environmentally sound technologies.

There are documents supporting the effects of irrigation, including the economic and social benefits, on the Ministry for the Environment and Ministry for Primary Industries website.

There are also articles available with a quick ‘Google’; for example, ‘Research surprise: intensive dairying helps build soil’ makes the point. And the point is that organic matter, which is generally quite high in New Zealand soils by global standards, is the key to water and nutrient retention.

In hot and dry conditions, the plants stop growing before the soil organisms stop breaking down the soil organic matter. (This is like a teenager going on eating food from the refrigerator while the parents are away; eventually the food runs out. And whereas the teenager might revert to takeaways, the soil micro-organisms simply die or ‘hibernate’.) The result is bare soils at risk of erosion by wind or rain, and which become ‘sediment’ in waterways. Sediment reduces clarity in water and creates ecological problems by cutting down light infiltration and settling on organisms.

Labour’s water policy contains several references to reducing sediment, for example, “Take action to protect waterways, wetlands and estuaries from excessive sedimentation caused by erosion and land use practices (including ‘spray and pray’) that lead to soil loss”.

From mid-to-late last century, the dust storms on the Canterbury Plains at certain times of the year were just part of what happened. They don’t any more. Irrigation has made the difference to soil quality.

Water quality is a different issue, and to maintain or improve it requires the use of modern technologies. Precision irrigation keeps water, and hence nitrogen, in the rooting zone. Using stored water for irrigation protects rivers and aquifers, and allows the maintenance of ecological flows. Storing water requires construction and hence funds, but, as shown in Canterbury, it can lead to enhanced recreational facilities.

Storing water has been suggested to be anti-environment. However, New Zealand, in contrast to most of the world, has a large renewable water resource. Water availability and the beautiful environment, as well as distance from super-powers, is already attracting overseas interest. All aspects of the environment need to be managed carefully, including what might appear to overseas people to be water wastage.

Concerns about irrigation leading to more dairy cows overlook the new technologies, including feeding regimes, composting barns, pasture species and urine patch identifiers, that reduce nitrogen excretion to the soil.

Without the irrigation schemes already in place, NZ’s real GDP would be considerably less than it is. The NZ Institute of Economic Research calculated in 2014 that the contribution of irrigation was $4.8 billion.

Of equal importance is the employment it has created, and hence the increased vibrancy of rural areas. This type of analysis, including the evaluation of risk:benefit, management of project applications and funding, and ensuring efficiencies of scale, was the focus of  Crown Irrigation Investments Ltd (CIIL). The projects that had reached stage 5 of ‘commitment’ had been judged to add value to NZ.

CIIL is now being wound down – not because it hasn’t done a good job, but because national irrigation projects are no longer a government priority. The opportunity for a co-ordinated and national approach is slipping away.

To achieve an efficient and productive future, NZ must stop jumping to conclusions without having analysed the implications and unintended consequences of the alternatives. Some of them are worse.

RIP Crown Irrigation Investments Ltd.

• Dr Jacqueline Rowarth has a PhD in soil science and has been analysing agri-environment interaction for several decades.

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