Grass can be planted with the use of any capable sowing machine. Unlike other crops, it regrows over time so you don't have to sow it after each harvest. Grass yields 32,000 litres per hectare. Fertilizing your grass field doesn't have any effect on its yields.
When you want to harvest this "crop" make sure it is fully matured unlike the regular crops. The yield is highest when it is at the last stage of growth.
On easy, normal and hard difficulty, grass is worth around 200 $, 100 $ and 50 $ per 1,000 litres respectively. It can be sold in the small wooden barn on your farm, near the green grass heaps around your map or at the Biogas plant.
The grass may also be turned into silage, a form of cow fodder. The silage can be processed at the biogas plant or cow pasture.