The whole question of maintaining the
supply of plant-foods in the soil concerns itself in the main with
the supply of these three substances.
The persistent fertility of dry-farms
In recent years, numerous farmers and some investigators have stated
that under dry-farm conditions the fertility of soils is not
impaired by cropping without manuring. This view has been taken
because of the well-known fact that in localities where dry-farming
has been practiced on the same soils from twenty-five to forty-five
years, without the addition of manures, the average crop yield has
not only failed to diminish, but in most cases has increased. In
fact, it is the almost unanimous testimony of the oldest dry-farmers
of the United States, operating under a rainfall from twelve to
twenty inches, that the crop yields have increased as the cultural
methods have been perfected. If any adverse effect of the steady
removal of plant-foods has occurred, it has been wholly overshadowed
by other factors. The older dry-farms in Utah, for instance, which
are among the oldest of the country, have never been manured, yet
are yielding better to-day than they did a generation ago.
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