dolomitic limestone be used magnesium is also supplied in suitable
form for plant food, Thus only nitrogen and phosphorus remain for
consideration.

Keeping in mind that systems of permanent profitable agriculture in
America must be founded upon an intelligent understanding of the
foundation principles involved, let us pray for strength to
acknowledge the truth and cease trying to deceive ourselves. The
truth is that by soil enrichment alone the average crop yields of
the United States could be doubled, with the same seed and seasons
and with but little more work than is now devoted to the fields; and
we should cease trying to deceive ourselves in the hope or belief
that the fertility of our soil will be maintained if we continue
year after year to take crops from the land and fail to make
adequate return.

Nitrogen is both the most abundant agriculturally and the most
expensive commercially of all the elements of plant food; and yet
there is a method by which it can be secured not only without money
but with profit in the process. The percentage of nitrogen in normal
soils decreases with depth, so that subsoils are almost devoid of
nitrogen. This would be more generally understood if it were known
that the supply of soil nitrogen in humid countries is contained
only in the organic matter.

This organic or vegetable matter consists of the partly decomposed
residues of plants, including the roots and fallen leaves which may
accumulate naturally, and the green manure crops, crop residues and
farm manure which may be supplied in farm practice. Thus the
nitrogen of a soil is measured approximately by its content of