Dry-Farming : A System of Agriculture for Countries under a Low RainfallWidtsoe, John Andreas
Science
Dry-Farming : A System of Agriculture for Countries under a Low Rainfall
Widtsoe, John Andreas
Dry farming
The great loss of soil moisture due to an accumulation of water in
the upper twelve inches is well brought out in the experiments
conducted by the Utah Station. The following is selected from the
numerous data on the subject. Two soils, almost identical in
character, contained respectively 17.57 per cent and 16.55 per cent
of water on an average to a depth of eight feet; that is, the total
amount of water held by the two soils was practically identical.
Owing to varying cultural treatment, the distribution of the water
in the soil was not uniform; one contained 23.22 per cent and the
other 16.64 per cent of water in the first twelve inches. During the
first seven days the soil that contained the highest percentage of
water in the first foot lost 13.30 pounds of water, while the other
lost only 8.48 pounds per square foot. This great difference was due
no doubt to the fact that direct evaporation takes place in
considerable quantity only in the upper twelve inches of soil, where
the sun's heat has a full chance to act.
Any practice which enables the rains to sink quickly to considerable
depths should be adopted by the dry-farmer. This is perhaps one of
the great reasons for advocating the expensive but usually effective
subsoil plowing on dry-farms. It is a very common experience, in the
arid region, that great, deep cracks form during hot weather. From
the walls of these cracks evaporation goes on, as from the topsoil,
and the passing winds renew the air so that the evaporation may go
on rapidly. The dry-farmer must go over the land as often as needs
be with some implement that will destroy and fill up the cracks that
may have been formed. In a field of growing crops this is often
difficult to do; but it is not impossible that hand hoeing,
expensive as it is, would pay well in the saving of soil moisture
and the consequent increase in crop yield.
How soil water reaches the surface
It may be accepted as an established truth that the direct
evaporation of water from wet soils occurs almost wholly at the
surface. Yet it is well known that evaporation from the soil surface
may continue until the soil-moisture to a depth of eight or ten feet
or more is depleted. This is shown by the following analyses of
dry-farm soil in early spring and midsummer. No attempt was made to
conserve the moisture in the soil:--
Per cent of water in Early spring Midsummer
1st foot 20.84 8.83
2nd foot 20.06 8.87
3rd foot 19.62 11.03
4th foot 18.28 9.59
5th foot 18.70 11.27
6th foot 14.29 11.03
7th foot 14.48 8.95
8th foot 13.83 9.47
Avg 17.51 9.88
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