uit may be checked in its work of
seed production by insects and diseases, and to secure good fruit it
is in many cases necessary to spray the fruits just as the leaves
are sprayed, to keep these insects and diseases in check.

The fruits of most plants, like the leaves, need light and air for
their best development, and it sometimes happens that the branches of
the fruit trees grow so thick that the fruits do not get sufficient
light and air. This makes it necessary to thin the branches or in
other words to prune the tree. Some trees also start more fruit than
they can properly feed and as a result the ripened fruits are small
and the tree is weakened. This makes it necessary to thin the fruits
while they are young and undeveloped.

PART II

Soil Fertility as Affected by Farm Operations and Farm Practices

THE FIRST BOOK OF FARMING

PART II

_Soil Fertility as Affected by Farm Operations and Farm Practices_

CHAPTER XVI

A FERTILE SOIL

What is a fertile soil?

The expression a fertile soil is often used as meaning a soil that is
rich in plant food. In its broader and truer meaning a fertile soil is
one in which are found all the conditions necessary to the growth and
development of plant roots.

These conditions, as learned in Chapter II, are as follows:

The root must have a firm yet mellow soil.

It must be well supplied with moisture.

It must be well supplied with air.

It must have a certain amount of heat.

It must be supplied with available plant food.

In order to furnish these needs or conditions the soil must possess
certain characteristics or properties.

These properties may be grouped under three heads:

Physical properties; the moisture, heat and air conditions needed by
the roots.

Biological properties; the work of very minute living organisms in the
soil.

Chemical properties; plant food in the soil.

PHYSICAL PROPERTIES OF A FERTILE SOIL

Three very important physical properties of a fertile soil are its

Power to take water falling on the surface.
Power to absorb water from below.
Power to hold water.

The fertile soil must possess all three of these powers. The relative
degrees to which these three powers or properties are possessed
determine more than anything else the kind of crops or the class of
crops that will grow best on a given soil.

These powers depend, as we learned in Chapter IV, on the texture of
the soil or the relative amou