Bradley found that the
soils of the great dry-farm wheat belt of Eastern Oregon contained,
after having been farmed for a quarter of a century, practically as
much nitrogen as the adjoining virgin lands. These determinations
were made to a depth of eighteen inches. Alway and Trumbull, on the
other hand, found in a soil from Indian Head, Saskatchewan, that in
twenty-five years of cultivation the total amount of nitrogen had
been reduced about one third, though the alternation of fallow and
crop, commonly practiced in dry-farming, did not show a greater loss
of soil nitrogen than other methods of cultivation. It must be kept
in mind that the soil of Indian Head contains from two to three
times as much nitrogen as is ordinarily found in the soils of the
Great Plains and from three to four times as much as is found in the
soils of the Great Basin and the High Plateaus. It may be assumed,
therefore, that the Indian Head soil was peculiarly liable to
nitrogen losses. Headden, in an investigation of the nitrogen
content of Colorado soils, has come to the conclusion that arid
conditions, like those of Colorado, favor the direct accumulation of
nitrogen in soils.
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