Police used pepper spray and accused some participants of violence against security forces.
Thousands gathered in the Polish capital, demanding a halt to cheap imports and environmental regulations they say harm their livelihoods.
Krzysztof is one of the protesting farmers.
"What is happening now is a tragedy. Our wheat and our other products - the prices are as they were thirty years ago and the costs keep increasing."
Warsaw police said several officers were wounded and around a dozen people detained.
Farmers across the EU have been calling for changes to restrictions placed on them by the bloc's Green Deal plan to tackle climate change.
They have also been demanding changes for customs duties on imports of agricultural products from Ukraine that were waived after Russia's invasion to be reimposed.
The situation has created a delicate balancing act for Donald Tusk's government in a year where it faces both local and European elections.
It is seeking to address farmers' concerns while also maintaining its staunch support for Kyiv.
On Monday, Tusk said Poland planned to ask the EU to ban imports of agricultural products from Russia and Belarus.
The prime minister has invited farmers' leaders for talks on Saturday (March 9).
