Gullies would more likely form on ground that is plowed and devoid of plants. This is because the top soil on ploughed ground is loose and directly exposed to the two main agents of erosion namely water and wind which easily carry it away when the weather is windy or wet.
The soil gets washed away by run off water gradually causing gullies to form on the ground.
A field covered with thick grass resists erosion because the roots of grass hold the soil firmly in place, and the leaves of the grass protect the soil from direct exposure to the sun, wind and rain.
