Strangely
enough, this is not true of the irrigated farms, operating under
like soil and climatic conditions. This behavior of crop production
under dry-farm conditions has led to the belief that the question of
soil fertility is not an important one to dry-farmers. Nevertheless,
if our present theories of plant nutrition are correct, it is also
true that, if continuous cropping is practiced on our dry-farm soils
without some form of manuring, the time must come when the
productive power of the soils will be injured and the only recourse
of the farmer will be to return to the soils some of the plant-food
taken from it.
The view that soil fertility is not diminished by dry-farming
appears at first sight to be strengthened by the results obtained by
investigators who have made determinations of the actual plant-food
in soils that have long been dry-farmed. The sparsely settled
condition of the dry-farm territory furnishes as yet an excellent
opportunity to compare virgin and dry-farmed lands and which
frequently may be found side by side in even the older dry-farm
sections. Stewart found that Utah dry-farm soils, cultivated for
fifteen to forty years and never manured, were in many cases richer
in nitrogen than neighboring virgin lands.
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