A letter from Dunsandel - Experts Challenged

W D Wrigley of Dunsandel writes to the Editor of NZ Farming

Your editorial, Cynical Labour beneath contempt (September 18) was entirely apt and I support it wholeheartedly.

Unfortunately, the anti-farmer anti-irrigator brigade has picked up a few fellow travellers along the way, not the least of these being your paper's stablemate, the Christchurch Press.

For some time now The Press has provided a forum for anyone prepared to produce a quasi­ expert opinion on the adverse effects of irrigation and dairying on our freshwater bodies.

These articles usually range from half­truths to outright embellishment (polite term for bull ...).

To be fair to The Press, they usually publish any correspondence promoting alternative viewpoints, but never with the same prominence as the original article.
 
The most recent and glaring example of this bias came when The Press published on its front page seven columns of complete embellishment under the headline "NZ dairy farms use as much water as 58.2 million people".

The article relied on contributions from agricultural economist Peter Fraser and farm consultant Dr Alison Dewes and was slanted to show dairying, especially that which relies on irrigation, as profligate users of a national resource, by comparing dairying's annual water use at 4.8 billion cubic metres with the amount used by the combined populations of many large cities.

I believe that Fraser and Dewes are wrong about the amount of water used by dairying, and challenge them through your paper to produce their supporting calculations.
  
My calculations are:
Approximate number of irrigated dairy farms 2000; 
average area 210 hectares; 
annual application of irrigation water 5000 cubic metres per hectare, 
for a total of 2.1 billion cubic metres; 5 million cows drinking 60 litres per day, and dairy shed use 60 litres per
cow per day, for a total of 219 million cubic metres - a grand total of 2.3 billion cubic metres.

These figuresare based on and are compatible with DairyNZ's 2015-2016 survey. I have excluded any effect attributable to non­milking livestock on the basis that these days they are rarely grazed on the home farm and that the amount of water they drink is insignificant compared to the volume used by the actual milking herd.

To provide some perspective, 2.3 billion cubic metres is about as much rain as fell on Canterbury on September 18. Other assertions in the article relating to
the cost of Labour's proposed water royalty are equally misleading and open to challenge.

Of much deeper significance is the question " Did Fraser and Dewes know and intend that the information they provided was going to be used to denigrate irrigated dairying?" There is nothing wrong with holding and expressing views, but when one dons the mantle of "expert" it is incumbent on that person to exercise great care in the presentation and dissemination of statistics, even more so in the white hot glare of a politically charged environment.

W D Wrigley
Dunsandel