Understanding Urine - Stop Taking the Piss

NZ Herald and NZ Listener Magazine have run - with increasing frequency and force - articles criticising the growth and expansion in NZ's diary industry. Much of this media reporting has been triggered and informed by the Parliamentary Commissioner for Environment's recent report on land use change and water pollution which shows a clear link between expanding dairy farming and increasing stress on water quality.

This article, by NZ Herald's writer on the NZ economy, was unusually to the point, and did not pull any punches.

My own research interest in this matter goes back a long way - being a South Islander (my rivers were the Oamaru Creek, the Kakanui River and the Waitaki River) - and over the past two decades thinking about water demand and raw water quality (Waikato River as drinking water source for Auckland).

Because of the issue of nitrate pollution I have recently been educating myself to better understand where the nitrogen actually comes from. To begin with, I had thought the main source of nitrogen contamination from pastureland in dry, relatively unfertile areas (such as North Otago and South Canterbury, was the zealous use of fertiliser. (This also being a source of phosphorous). I thought that nitrogen rich fertiliser was dissolving in surface water and then running off into rivers and into groundwaters.

That is happening, but the nitrogen cycle is more complex than that. Reading this Listener article (which you have to subscribe to see in entirety) alerted me to the fact that cow piss contains lots of nitrogen, and that cow urine is the main source of nitrogen contamination in natural waters (not nitrogen from fertilisers).

This was interesting. Good to have a new fact get in the way of my opinion.

So I did some research, and found this briefing from Environment Waikato, which says this, I have added emphasis:

Nitrogen is one of the most important major nutrients
in the New Zealand farming system. It enters the
system either by clover root nodules taking the
nitrogen from the air and fixing it in a form the
clover can use. It also enters as bought-in feed or
as nitrogenous fertiliser. Plants take up the nitrogen
returned to the soil in the form of urine, dung and
leaf litter. A small proportion of this nitrogen is
converted to milk, meat and wool.

What I take from this is something new about where the nitrogen that gets in the urine is coming from. It is taken from the atmosphere (air contains 78% nitrogen) during the growth of certain forms of pasture plants - especially clover. Cows eat the pasture which contains nitrogen taken up from fertiliser AND ALSO from the atmosphere. Hardly any of the nitrogen consumed by the cow is converted into milk or meat. It is disposed of as urine.


What has not been made crystal clear in the science that I have read in popular press is that much of the nitrogen in cow urine comes from the atmosphere.

We know that cows eat grass and convert organic matter into milk.

But it's not that simple.

As they grow, clover and other pastureland plants convert atmospheric nitrogen into digestable chemicals which are also consumed by the cow (along with the organic materials in the leaves and stalks), and nitrogen rich left-overs are mostly separated in the cow's stomach and then passed out as ammonia in urine. (And yes, plants also absorb nitrogen from fertiliser).

The more cows on an area of land eating natural pasture, the more nitrogen from the air is being transformed into ammonia on the ground (urine) where it is converted into nitrates by bacterial action. Nitrates can be used by plants, but if there’s too much it leaches past the roots, into the ground, and into groundwater reservoirs, where it slowly accumulates.

Scientists call these urine patches nitrogen hot spots.

This is a tragedy of the commons like global warming in reverse.

Instead of atmospheric carbon dioxide increasing through fossil fuel burning, it’s atmospheric nitrogen conversion into groundwater nitrate contamination as a by-product of dairy herd factory production of milk from pasture. Intensive dairy-farming is a machine sucking inert nitrogen from the atmosphere and pouring chemically active nitrate contaminants into natural water resources.

Asking farmers to clean up their factories is a bit like asking car owners to drive less and slow climate change.

 The question: “Can the conflict between the dairy farming economic boom and polluted water be resolved?” is a good one to ask, but it begs another: “by whom?” When Government sacked Environment Canterbury’s elected councillors and appointed commissioners to oversee difficult water allocation problems, it cited political advice that “ECan was science led, but that it should be science informed”.

You can't have it both ways guys. Now we have elected councillors and water scientists not being trusted by government. It's reminiscent of another time when government decided it couldn't trust local government with climate change. Took it into the Minister's office. Looks like that's where cow piss is headed too. But isn't it time to stop pissing about...?