Most agricultural vehicles are legally prohibited from entering Slovak motorways and expressways.
Otherwise they need an e-vignette up to 3.5 tonnes and use the MYTO if they are over 3.5 tonnes.
Exemptions can be made if pre-registered with the National Motorway Company (e.g. vehicles performing specific maintenance, rescue, or state-ordered agricultural tasks).
Related articles:
What vehicles need a Slovak e-vignette?
Do company vans need a Slovak e-vignette?
Where can I buy the Slovak motorway e-vignette?
Where can I register for the MYTO and get the on-board unit (OBU)?