162 ELEMENTARY AGRICULTURE 
it time to decay and become well mixed- with the soil 
particles. 
We can not rely on livestock for the production of all 
the humus needed on the farm. We must grow such 
crops as peas, clover, soy beans, and vetch and plow the 
crops under while they are green. This is known as green 
manuring. Some farmers let their land lie out to grow 
up in weeds in order that they may turn under the weeds 
to add organic matter to the soil. 
Fig. 120.—A ootton field washing away. 
Stubble, roots of plants, and old straw may be plowed 
under in the fall, and they add much organic matter to 
the soil. 
Some farmers prefer to “hog down” or “pasture off the 
crop” grown for green manure and then plow under the 
refuse and manure. By doing this, greater profit is made 
from the crop. 
Importance of Good Drainage.—Plants do not grow 
well on poorly drained soils. When free water is too 
near the surface soil, it prevents the circulation of air 
and heat into the soil and subsoil This causes the roots 
