David Shaw would like to talk about Jersey cows.

But his job today is to talk about muck – storing it, spreading it, and doing sums about it for the Government.

He is probably Yorkshire's best-informed farmer on the subject of Nitrate Vulnerable Zones (NVZs) – where the spreading of manure and fertilisers is controlled because the land drains into rivers which are in danger of failing Environment Agency tests for nitrogen compounds (nitrates).

New rules for NVZs take effect on January 1 and new NVZs take effect a year later. There will be new limits on the amount of nitrogen which can fall on a hectare of land and new limits on when – because, in theory, nitrates are most likely to trickle away to the rivers between August 1 and December 31, when plant uptake is at its lowest.

The old "closed periods" for spreading were up to six weeks; the new ones could be five months, depending on type of farm and type of soil. With safety margins, some pig and poultry producers will need storage for 26 weeks' worth of wash-out from their sheds and dairy farmers for up to 22.

Mr Shaw's farm drains into the Derwent, south of York, a few yards from where Yorkshire Water extracts for Sheffield.

Because of that, Grey Leys Farm at Elvington has been in an NVZ since 2002.

Up to now, a two-month slurry tank has been enough. Now, he appears to need a new one, for 154 days. That, and shifting muck about to meet other elements of the compliance formula, would cost £19,000 a year, more or less – depending on some detail yet to be clarified.

He is the fourth generation of his father's family to run the farm. They came in 1876 and bought in 1911.

When Mr Shaw came back from college and work experience in 1968, it was an old-fashioned mixed farm – sheep, cows, beef steers, sows, chickens, potatoes, wheat.

But the market was in favour of specialisation and so was the Ministry of Agriculture Fisheries and Food. Mr Shaw recalls a MAFF inspector coming to check some building work and staying to help with the milking..."He said we were the people who were going to solve the country's food problem."

It's a while since Government officials talked that sort of language. But Mr Shaw has managed to stay afloat, with the help of wife Anne and two full-time employees.

His son is studying genetics at university and his daughter works as a buyer for the Co-op – an organisation he respects.

With a bit of renting, he runs 167 hectares, supporting 320 milking Jerseys, with 200 followers.

He grows barley, lucerne, maize and grass, to make himself nearly self-sufficient in feed, and sells to Longley Farm, the Holmfirth creamery which takes most of Yorkshire's Jersey production. Having been blooded early, Mr Shaw took an interest in the science behind NVZs. It has been more or less forgotten that the first concern about nitrates in water was that they might cause "blue babies".

Since the concern was raised, in 1949, there has been one blue-baby case that Mr Shaw knows of in which nitrates were implicated and the nitrates were naturally-occurring.

But, of course, the argument has moved on to absorb concerns about the effect of pollution on the things that live in the water itself. The aim is 50 parts per million. Mr Shaw recalls that 500 ppm was the level said to be harmful to babies. He suspects the World Health Organisation simply divided by 10, to be on the safe side. If anybody has a more scientific explanation, he would like to hear it.

Human sewage pours into some rivers by the tonne, he points out. But most farmers would not deliberately throw away any slurry. The idea of the revised NVZ rules is to limit the run-off from it.

Defra says 60 per cent of river pollution comes from farms. The NFU calculates that all the expensive new slurry tanks will change their nitrates contribution by less than one per cent.

Defra was quite sympathetic to these arguments for many years, which is why it had a lot of catching up to do when the EC got tough. Now, having been back through the small print, the politicians have accepted that the argument is more or less over. Mr Shaw says important details are to be finalised. In particular, the proposed limit of 170 kgs of nitrogen per hectare, for grassland, would mean cuts in stocking density even for his own free-range-style farm, and Defra did promise to keep negotiating for a derogation for a 250 kgs per hectare (kph) limit. All seems to have gone quiet on that front but it is "absolutely critical", he says.

Meanwhile, for some reason, arable land can have only 170 kph of organic fertiliser, from livestock, but as much inorganic fertiliser, from the chemicals industry, as the crop needs. Mr Shaw has argued detail on the subject for the Quality Milk Producers, Jersey Cattle Society and NFU, but even he does not understand that little loophole.

Whatever the costs are, they will have to be passed on. Dairy farmers are only just breaking even as it is, he says, and two a day are still getting out of the business and being replaced by imports.

The supermarkets are better than they were when desperate dairymen were running flying pickets through the night. The turning point, says Mr Shaw, was the intervention of the Women's Institute, which threatened a boycott of products which were not fair to farmers.

Suddenly, executives who had ignored the NFU were sat across a table asking what the problem was.

Sourcing and security of supplies have become issues. Several big chains now run their own supply groups, which means they do hear what the farmers say. "But now they are having another price war over milk when they should be talking about a sensible pricing structure," says Mr Shaw.

"I asked a Tesco representative if all this environmental legislation would cost 2p a litre. She said it would be more than that."

He suspects nitrates control is paving the way for a similar crackdown on phosphates. Most of the phosphates in the rivers, he says, come from household detergents. But farming is a source. Which will the Government tackle first, he wonders?

At 59, this is his 40th year in the dairy business. His dad kept black-and-whites. Mr Shaw milked Guernseys as a student but felt "they didn't really like one another".

He can talk about the virtues of Jerseys all day. Some black-and-whites are finished after two or three lactations. He sells Jerseys with life left in them after seven.

Meanwhile, they average 5,000 litres a year each, giving the same fat and protein as a bigger cow would in twice the milk.

In the NVZs debate, the difference between breeds was an important one, which the bureaucrats would not have recognised without the NFU, he says.

Defra's new maps of NVZs are at http://tinyurl.
com/3gquou