Napier-based farming expert Barrie Ridler has some answers for farmers struggling to curb their nitrogen leaching.

Dairy farmers, especially in the Tararua District, are waiting to see how Horizons Regional Council reacts to the Environment Court's April declarations - but are already under pressure to reduce the nitrogen they leach.

Mr Ridler says matching stock numbers to pasture growth is the secret, and keeping the two in balance will limit greenhouse gas emissions.

Any animal additional to what a farm's pasture can support will be a cost and not add to profit, he said.

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"If you are slightly understocked you will always do better than if you are overstocked."

Since the early 2000s, the government and farming groups have been pushing for higher production, he said.

"People think more production is more profit. That's wrong, and has been wrong for 10 years now."

His seven-second soundbite is: "If you get the economics right, the environment will follow."

Mr Ridler lives in Hawke's Bay and has been a dairy farmer, a sheep and beef farmer, a Massey lecturer on farm management and the manager of research farms.

With the help of Christchurch company Systems Software Instrumentation, he's put together a computer model to analyse on-farm basics.

The model feeds in information, and can add nitrogen leaching limits to the mix to assess the effect of any action.

Farmers can find out exactly how many animals are profitable for their business, and know the rest are a cost.

"You need to find out what isn't making you money. Once you have adjusted that a lot of other things become obvious."

Any feed bought in should only be for "pinch points" of a maximum of four weeks, he said. Extra feed and extra nitrogen fertiliser are extra costs that can only be recouped if the price of a kilo of milk solids gets back up to $8.50 or $9.

Mr Ridler says that's not going to happen: Europe is storing milk powder it can't sell, and ready to ramp up production if the milk price rises.

The United States can make milk more cheaply than New Zealand's high-intensity farming systems. Feed costs half as much there, and cows produce twice as much milk - up to 1000kg of milksolids a year.

He predicts farmers increasing stock numbers and planning to get a capital gain when they sell will be disappointed. "Any business sold is based on the profit it can make."

With stock raised mainly on pasture nitrogen, leaching will decrease, enabling most farmers to meet the limits set in Horizons' One Plan. There will also be fewer environmental effects for taxpayers and ratepayers to clean up.

"The downstream effects from farms are leading to chaos and huge damage to the environment and people's health in New Zealand," he says.

"There's no point in trying to strong-arm farmers to do anything. But as soon as anybody gets the fact they are paying more than what it's worth, from that point on it's like night and day. They just suddenly say 'Why didn't I see that before'?"