• Bert Quin

This is no April fools joke; we must tighten agricultural nutrient cycles

Nutrient cycling in natural ecosystems is incredibly efficient, having had immense periods of time to develop. It is incredibly arrogant of mankind to come along and impose totally different, man-made farming systems where natural ecosystems used to be, and assume that everything will be fine and dandy.

We initially got away with it with the introduction of ryegrass-clover pastures over 10 million ha of New Zealand's previous bush and native forests. Unlike Australia, NZ had , like much of Europe, higher, more predictable rainfall and soils that could consequently accumulate organic matter rapidly, avoiding excess leaching and run-off of nutrients

The introduced ryegrass-clover pastures were excellent for grazing, especially under some form of rotational grazing, unlike the set-stocking system used for far too long on Australia's very low-nutrient ecosystems.

Our ryegrass-clover pastures had a beautifully inbuilt control system. As the clover fixed more atmospheric N, more of this became available to ryegrass, which grew more and started to suppress clover growth through shading. So less fixed N became available for ryegrass, allowing the clover became more competitive again. And so on and on it went.

In the 1980's, farmers started to see that nitrogen (N) fertiliser could be used strategically to boost pasture production in a feed pinch, such as extending late autumn production or kicking it off earlier in spring. Over about a decade, this became a standard practice that didn't seem to have any ill effects. The N applications were followed by a temporary decline to clover production, so total production stayed more or less the same.

But in the late 80's and early 90's,, dairy farmers found that they could greatly increase production and profitability by simply applying more and more fertiliser N, even when it got to the stage of essentially eliminating clover from our pastures. Lower fertiliser N prices, helped by NZ's 'think big' Kapuni urea plant, accelerated this development. More and more P, K and S were being applied also. New ryegrass varieties with more potential to respond to fertiliser N were developed. Typical dry matter (DM) production rose by up to 50% from the old standard of 12,000 kg DM/ha annually. It also allowed profitable dairying on many of NZ's shallower soils, especially with irrigation.

With the increasing use of N fertiliser and other nutrients, our dairy farming is no longer a sustainable ecosystem; rather, it has become a very nutrient-leaky trap, with ever-declining biodiversity, plant root depth, and resilience to drought and disease.

It is still referred to by the industry as a 'permanent pasture system', but nothing could be further from the truth. 'Perennial ryegrasses' seldom survive more than 3 years before needing costly resowing, involving more soil disturbance and particulate run-off. Brought in animal feeds such as PKE typically makes up 20% of our 'pasture-fed' cows' diet.

Dairy farmers are becoming trapped in an ever-increasing spend on fertiliser, herbicides, pest control, resowing, brought-in feed, animal health etc, just to stay solvent.

This increasing overload of fertiliser and chemicals is already playing havoc with our water quality. The increased dietary uptake of N leads to increasing N deposition in urine patches, from which most of the nitrate in our waterways and nitrous oxide GHG emissions come from.

How, in the face of all this, can scientists be bemused by, and even strongly critical of, the growing farmer-driven move towards regenerative farming?