any time.

To mix manures and organic matter with the soil. The more thoroughly
manure is distributed through the soil the more easily plants will get
it and the greater will be its effect on the soil.

To destroy the insect enemies of the plant by turning them up to the
frost and the birds.

To kill weeds. Weeds injure crops:

They waste valuable moisture by pumping it up from the soil and
sending it out into the air through their leaves. In this way they do
their greatest injury to crops.

They crowd and shade the crop.

They take plant food which the plant should have.

Spading and plowing bring about conditions necessary for the sprouting
or germination of seeds.

Spading and plowing also tend to bring about conditions necessary for
the very important work of certain of the soil bacteria.


PARTS OF A PLOW

It will be found that a good farm plow has the following parts (Fig.
50):