Dry-Farming | Page 3

by what means surface evaporation may be
prevented or regulated. The soil-water, of real use to plants, is that
taken up by the roots and finally evaporated from the leaves. A large
part of the water stored in the soil is thus used. The methods whereby
this direct draft of plants on the soil-moisture may be regulated are,
naturally, of the utmost importance to the dry-farmer, and they
constitute another vital problem of the science of dry-farming.
The relation of crops to the prevailing conditions of arid lands offers
another group of important dry-farm problems. Some plants use much
less water than others. Some attain maturity quickly, and in that way
become desirable for dry-farming. Still other crops, grown under humid
conditions, may easily be adapted to dry-farming conditions, if the
correct methods are employed, and in a few seasons may be made
valuable dry-farm crops. The individual characteristics of each crop
should be known as they relate themselves to a low rainfall and arid
soils.
After a crop has been chosen, skill and knowledge are needed in the
proper seeding, tillage, and harvesting of the crop. Failures frequently
result from the want of adapting the crop treatment to arid conditions.
After the crop has been gathered and stored, its proper use is another
problem for the dry-farmer. The composition of dry-farm crops is
different from that of crops grown with an abundance of water. Usually,
dry-farm crops are much more nutritious and therefore should
command a higher price in the markets, or should be fed to stock in

corresponding proportions and combinations.
The fundamental problems of dry-farming are, then, the storage in the
soil of a small annual rainfall; the retention in the soil of the moisture
until it is needed by plants; the prevention of the direct evaporation of
soil-moisture during; the growing season; the regulation of the amount
of water drawn from the soil by plants; the choice of crops suitable for
growth under arid conditions; the application of suitable crop
treatments, and the disposal of dry-farm products, based upon the
superior composition of plants grown with small amounts of water.
Around these fundamental problems cluster a host of minor, though
also important, problems. When the methods of dry-farming are
understood and practiced, the practice is always successful; but it
requires more intelligence, more implicit obedience to nature's laws,
and greater vigilance, than farming in countries of abundant rainfall.
The chapters that follow will deal almost wholly with the problems
above outlined as they present themselves in the construction of a
rational system of farming without irrigation in countries of limited
rainfall.

CHAPTER II
THE THEORETICAL BASIS OF DRY-FARMING

The confidence with which scientific investigators, familiar with the
arid regions, have attacked the problems of dry-farming rests largely on
the known relationship of the water requirements of plants to the
natural precipitation of rain and snow. It is a most elementary fact of
plant physiology that no plant can live and grow unless it has at its
disposal a sufficient amount of water.
The water used by plants is almost entirely taken from the soil by the
minute root-hairs radiating from the roots. The water thus taken into the
plants is passed upward through the stem to the leaves, where it is
finally evaporated. There is, therefore, a more or less constant stream of
water passing through the plant from the roots to the leaves.
By various methods it is possible to measure the water thus taken from

the soil. While this process of taking water from the soil is going on
within the plant, a certain amount of soil-moisture is also lost by direct
evaporation from the soil surface. In dry-farm sections, soil-moisture is
lost only by these two methods; for wherever the rainfall is sufficient to
cause drainage from deep soils, humid conditions prevail.
Water for one pound dry matter
Many experiments have been conducted to determine the amount of
water used in the production of one pound of dry plant substance.
Generally, the method of the experiments has been to grow plants in
large pots containing weighed quantities of soil. As needed, weighed
amounts of water were added to the pots. To determine the loss of
water, the pots were weighed at regular intervals of three days to one
week. At harvest time, the weight of dry matter was carefully
determined for each pot. Since the water lost by the pots was also
known, the pounds of water used for the production of every pound of
dry matter were readily calculated.
The first reliable experiments of the kind were undertaken under humid
conditions in Germany and other European countries. From the mass of
results, some have been selected and presented in the following table.
The work was done by the famous German investigators, Wollny,