South Canterbury farmers are grappling with Environment Canterbury's new rules on further intensification of land.
ECan's Land and Water Regional Plan caps nitrogen discharges from farms, based on a four-year average from 2009-13.
The plan's architect, Peter Constantine, spoke to about 70 farmers and industry agents in Waimate last week.
It would take more than eight generations for water quality to be restored, he said.
A reference group of farmers is looking at how to allocate the nitrogen load, after a strong reaction against initial proposals from the South Canterbury Coastal Streams zone committee.
The allocation of nitrogen is higher for land within the Hunter Downs and Waihao Downs irrigation schemes' 27,000 hectare uptake area.
ECan scientist Ned Norton said the extra tonnage of n-losses in the two irrigation schemes was being revised "because part of the community wants high emitters to do more work, and to increase flexibility for low emitters.
"We can't afford to have everybody in the zone moving up to ten. If that happened the increase in the load associated with that would completely blow out our environmental outcomes.
"We need to find a way of allowing the intensification ... an allowance for dairy support might be a way of doing that."
Farmers told the Central South Island Farmer dryland dairy support farms in the upper Waihao discharge about 9kg of nitrogen/ha/yr. A dairy farm on the same soil would discharge 18kg/ha.
ECan has said it's not interested in properties leaching less than 10kg/ha/yr.
All other farms must comply with nutrient management rules, or apply for resource consent. Development is permitted, but "the development can't cause an increase in nitrogen loss below the root zone and therefore eventually to water".
In addition, properties need farm environment plans identifying risks to water quality, and goals to reduce these.
Farmer Sue Wigley said the proposed limits were unfair.
"What about the people doing everything by the book and they can't do more because their baseline average is low, yet the person next door doing 35kg can carry on? It's inequitable."
Zone committee chairman Robin Murphy said the proposed limits were designed around values including ensuring economic and community growth.
Constantine said every property should have a baseline calculation now.
"We've had conversations with banks and they're very interested in these numbers because they will influence how much they will lend on properties."
- The Timaru Herald