ers.

It will be seen that all these classes of properties are necessary to
furnish all the conditions for root growth.

The proper chemical conditions require the presence of both physical
and biological properties and the biological work in the soil
requires both chemical and physical conditions.

From the farmer's standpoint the physical properties seem to be most
important, for the others are dependent on the proper texture,
moisture, heat and ventilation which are controlled largely by
tillage.

Therefore the first effort of the farmer to improve the fertility of
his soil should be to improve his methods of working the soil.

Every one of these properties of the fertile soil, and consequently
every one of the conditions necessary for the growth and development
of plant roots, is influenced in some way by every operation performed
on the soil, whether it be plowing, harrowing, cultivating, applying
manure, growing crops, harvesting, or anything else, and the
thoughtful farmer will frequently ask himself the question: "How is
this going to effect the fertility of my soil or the conditions
necessary for profitable crop production?"

MAINTENANCE OF FERTILITY

The important factors in maintaining or increasing the fertility of
the soil are:

The mechanical operations of tillage, especially with reference to the
control of soil water.

The application of manures and fertilizers, especially with reference
to maintaining a supply of humus and plant food.

Methods or systems of cropping the soil, with reference to economizing
fertility.

CHAPTER XVII

SOIL WATER

The more important tillage tools and tillage operations we studied in
Chapters XI and XII. They will be noticed here only in connection with
their influence over soil water, for in the regulation of this
important factor in soil fertility the other conditions of fertility
are also very largely controlled.

IMPORTANCE OF SOIL WATER

"Of all the factors influencing the growth of plants, water is beyond
doubt the most important," and the maintaining of the proper amount of
soil water is one of the most important problems of the thinking
farmer in controlling the fertility of his soil.

NECESSITY OF SOIL WATER

The decay of mineral and organic matter in the soil, and the
consequent setting free of plant food, can take place only in the
presence of moisture. The plant food in barn manures and crops plowed
under for green moisture,