st 5 .01 34
August 17 .06 222
September 2 .18 634
September 17 .22 760
October 2 .21 728

NOTE VII. (p. 188).

NITROGEN AS NITRATES IN ROTHAMSTED SOILS AFTER BARE FALLOW IN LB.
PER ACRE.

------------+-----------+---------------------------+-----------+----------
| Alternate | Four-course rotation. | |
| Wheat +-----------+---------------+ |
Depth of | and | Super- | | Claycroft | Foster's
Soil. | Fallow. | phosphate | Mixed Manure. | Field. | Field.
| | only. | | |
+-----------+-----------+-------+-------+-----------+----------
| 1878. | 1878. | 1878. | 1882. | 1881. | 1881.
------------+-----------+-----------+-------+-------+-----------+----------
| lb. | lb. | lb. | lb. | lb. | lb.
1st 9 ins. | 28.5 | 22.3 | 30.0 | 40.1 | 16.4 | 14.6
2d 9 ins. | 5.2 | 14.0 | 18.8 | 14.3 | 26.5 | 24.6
3d 9 ins. | - | - | - | 5.5 | 15.9 | 17.3
------------+-----------+-----------+-------+-------+-----------+----------
Total | 33.7 | 36.3 | 48.8 | 59.9 | 58.8 | 56.5
------------+-----------+-----------+-------+-------+-----------+----------

CHAPTER V.

THE POSITION OF PHOSPHORIC ACID.

We now come to consider the position of phosphoric acid in agriculture.
The question is, however, very much simpler in its nature than that of
nitrogen, and may be consequently discussed in a much shorter space.

Most soils, as we have already had occasion to point out, are better
supplied with available ash-plant ingredients than available nitrogen
compounds. The quantity of phosphoric acid absorbed by the plant is also
less than that of nitrogen; and lastly, the different chemical compounds
of phosphoric acid occurring in the soil are not nearly so numerous as
those of nitrogen. Phosphoric acid, however, must be regarded as ranking
next to nitrogen in its importance as a soil-constituent.

_Occurrence of Phosphoric Acid in Nature._

That phosphoric acid is of universal occurrence may be assumed from the
fact of the almost universal occurrence of vegetable life on the
earth's surface