A man was arrested by police after 12,000 litres of liquid manure was sprayed outside the office of Quebec's professional farmers' union on Monday, police said.

A 56-year-old man from Henryville, south of Montreal, was arrested by Longueuil police and taken to hospital for an evaluation.

According to police, a tractor pulling a tank of the semi-liquid manure sprayed the substance in the parking lot of the Union des Producteurs Agricoles (UPA) office about 6:30 a.m.

Patrice Juneau, a spokesman for the union, said the suspect is a dairy farmer who is facing financial difficulties and the union didn't wish to file a criminal complaint against him.

Longueuil police said he could still face a mischief charge, but the exact motivation for his alleged actions remained unclear.

Police said there was no danger to people living nearby, but cleaning the product from the lot and the building gave off a strong and nauseating odour.