1st six 2d six 3d six
inches. inches. inches.
Percentage of phosphoric acid .249 .134 .172
Nitrogen 1.62 .092 .064
Equal to ammonia .198 .112 .078

"In the upper six inches, as will be seen, the percentage of both
phosphoric acid and nitrogen, was larger than in the two following
layers, while the proportion of nitrogen in the six inches of surface
soil, was much larger than in the next six inches; and in the third
section, containing no visible particles of root-fibres, only very
little nitrogen occurred.

"In their natural state, the three layers of soil contained:

1st six 2d six 3d six
inches. inches. inches.
Moisture 17.16 18.24 16.62
Phosphoric acid .198 .109 .143
Nitrogen .134 .075 .053
Equal to ammonia .162 .091 .064
Lbs. Lbs. Lbs.
Weight of one foot square of soil 60 61 63

"Calculated per acre, the absolute weight of one acre of this land, six
inches deep, weighs:

Lbs.
1st six inches 2,613,600
2d six inches 2,657,160
3d six inches 2,746,280
=========

"No great error, therefore, will be made, if we assume in the subsequent
calculations, that six inches of this soil weighs two and one-half
millions of pounds per acre.

"An acre of land, according to the preceding determinations, contains:

1st six 2d six 3d six
inches, inches, inches,
Lbs. Lbs. Lbs.
Phosphoric acid 4,950 2,725 3,575
Nitrogen 3,350 1,875 1,325
Equal to ammonia 4,050 2,275 1,600
===== ===== =====

"The proportion of phosphoric acid in six inches of surface soil, it
will be seen, amounted to about two-tenths per cent; a proportion of the
whole soil, so small that it may appear insufficient for the producti