i 8 
COLORADO EXPERIMENT STATION 
plowed and the unstirred soil, making a mulch that prevents the water 
from rising through the plowed land, and it creates large air spaces 
in the soil. These tend to dry out the soil rapidly and to weaken the 
plants growing in it. 
All manure used in dry land farming should be applied as a light 
top dressing to grain, grasses or alfalfa. It then acts as a mulch, help¬ 
ing to retain moisture in the soil. The finer particles are impercept¬ 
ibly absorbed by the soil, the harrowings required by these crops 
slowly work the manure into the soil without making air spaces and 
the manure becomes as great a help as it is a detriment when plowed 
under unrotted. 
retaining moisture in the soil. 
When dry land soil has been loosened to a good depth to form 
a reservoir, and it is porous and fine grained, the water from a rain 
slowly moves downward through it until absorbed, and each minute 
grain of earth becomes covered with an invisible filrn of moisture. 
When these minute grains of soil are in close contact with one 
another, there is a constant movement of the water in the films 
surrounding them, the water flowing from a wet grain to a dryer 
one. After a rain the sun and the wind dry out the surface soil and 
carry away the moisture contained in it. Then the water from the 
damper soil below moves upward to wet the surface grains and is in 
turn evaporated. This movement continues in land not cultivated and 
extends to a depth of many feet, often, in a dry time, taking out of 
the soil, in a week moisture equal to more than an inch of rainfall. 
When the surface soil is stirred after a rain, the tiny grains are 
separated so that the water does not easily pass from one to another. 
The movement of the moisture is checked and evaporation is greatly 
reduced. Such shallow cultivation is called an earth mulch, because 
it has a similar effect in holding the moisture in the soil, as that 
effected by a mulch of straw or a covering of boards. 
The dry land farmer’s supply of moisture for his crops depends 
upon his skill and judgment in maintaining an earth mulch over his 
cultivated fields. No set rules can be given. He should study the 
principles governing the absorption and movement of water in the 
soil, as here given, until he thoroughly understands and appreciates 
them. Then he can intelligently conduct the farm operations for 
maintaining the earth mulch. 
The deeper the earth mulch, the better it will prevent evaporation 
from the soil. For cultivated crops a general rule, with many excep¬ 
tions, is to keep the mulch three inches in depth. With trees, four to 
six inches is better. Seeds must be planted below the earth mulch 
so that they will be in moist soil and the mulch must not be so deep 
as to prevent the young plants from coming up. With growing wheat 
and other grains, the mulch must not be made so deep as to put the 
roots in . dry soil. 
A good rain packs the loose surface soil and destroys the earth 
