Other parties who want to join the court proceedings have until 5pm on Friday to register their interest. Mr Carlyon expects Federated Farmers and others will join, as they did the last time the One Plan was in the Environment Court.
The court action may be causing confusion and doubt among farmers, but the council is still issuing resource consents.
There was little likelihood people would have to redo them as a result of the court action, Dr Peet said.
The council has taken legal advice about what it can do if people refuse to get resource consent.
A decision by the Environment Court could make Horizons revisit the One Plan, and begin a long legal process.
Dr Peet was disappointed about that, because he said the council had been making steady progress on implementing the One Plan for three years.
"The frustrating part for the council is that we've seen significant nitrogen reductions."