The maximums will apply to dairy, intensive sheep and beef, commercial vegetable growing and cropping in Horizons' target catchments - the closest to Whanganui being the coastal lakes area south of Whanganui and large parts of Rangitīkei.
The new leaching limits are higher because recent science has found more nitrogen was being leached than originally supposed.
"It's just a recalibration, not an increased allowance. The same amount of farm activity is going in but different numbers are coming out. The science informing the way the leaching rights are calculated has been amended," Horizons councillor Nicola Patrick said.
People who can't meet the numbers on the new table can apply to be considered for consent if they can show not meeting the numbers isn't critical for their area and that there are other things they will do to offset their impact.
Patrick has been told those people will have to meet a high threshold.
She said the changes could be unfair to landowners who got consent because they leach less than the first numbers in the table.
Also, some of the consents that inspired environment groups Environmental Defence Society and Fish & Game to take Horizons to the Environment Court in 2017 may have been given terms they wouldn't get under this proposed plan change.
"Reviews may be necessary, to ensure fairness," Patrick said.
Fellow Whanganui Horizons councillor David Cotton voted against notifying the plan change. The environment groups have said they would prefer the matter to go straight to a Board of Inquiry or the Environment Court, and he fears it will be appealed and end up in court.
"I'm a strong believer that communities fix rivers and issues, not courts," he said.
The proposed change is now open for submissions by anyone interested. People submitting should say whether they support or oppose some or all aspects of the change. They need to include information to back up their views.
The deadline for submissions is October 21. Those making them will also have a chance to present their views and evidence to a panel of commissioners when the proposed plan change is heard.
For more information and a submission form, go to www.horizons.govt.nz.