In the prolonged summer drought, farmers noticed that grass stayed green longer in their hayfields than in their pastures.
While hayfields kept growing, pastures turned brown. Cows ran out of grass to graze.
The difference is in the length of the roots. Grass that is grazed every day doesn't develop roots as deep as grass of the same species allowed to grow uncut for a month.
"Allowed to grow, grass roots will go down and find water," said Dennis Hancock, University of Georgia Extension forage specialist.
Hancock talked about basic biology of grass at the annual Crop Management Conference held by University of Missouri Extension in Columbia.
Forage crops can withstand the usual summer dry periods, Hancock said. But they must be given a chance to grow and develop deep roots.
The unseen loss from continuously grazed pastures is the killing of roots, he said. If leaves are continuously clipped, the roots die back. There's not enough photosynthesis to feed the roots. That's when lack of roots cuts the supply of water to the leaves.
Lack of strong roots on pasture grasses results in great loss to livestock producers.
Unmanaged grazing cuts losses further. On continuously grazed pastures, cattle get only 30 to 40% of the growth. Rotational grazing, moving livestock off the pasture before all the leaves are eaten, improves total growth.
Dividing a pasture into just four paddocks and rotating animals improves efficiency to above 60 %. "There is lots of room for improvement," the Georgia specialist said. "If you had only 30% efficiency feeding your corn, you would do something about it."
In Georgia, grazing dairies increased grazing efficiency to 80%. They rotate cows to new paddocks after every milking.