Briefly explain why the tyres of tractor are large and wide?
To reduce pressure on the ground in order to prevent wheels sinking into soft ground.
Large and wide tyres have a larger surface area. Pressure is inversely proportional to surface area. So for a given force the pressure will be reduced with a larger surface area.
Reducing pressure reduces the damage that the wheels do to the ground. Thus the amount that the wheels sink into the ground will be reduced. For a tractor this is useful because they are often driven over soft ground.