round numbers, every six inches of soil weighed per acre 2-1/2
millions of pounds, which agrees tolerably well with the actual weight
per acre of the preceding soil.

"The amount of phosphoric acid and nitrogen in each six-inch layer was
determined separately, as before, when the following results were
obtained:
In Dried Soil.

First six Second Third six
inches. six inches. inches.
Percentage of phosphoric acid .159 .166 .140
Nitrogen .189 .134 .089
Equal to ammonia .229 .162 .108

"An acre, according to these determinations, contains in the three
separate sections:

First six Second Third six
inches. six inches. inches.
lbs. lbs. lbs.

Phosphoric acid 3,975 4,150 3,500
Nitrogen 4,725 3,350 2,225
Equal to ammonia 5,725 4,050 2,700

"Here, again, as might naturally be expected, the proportion of nitrogen
is largest in the surface, where all the decaying leaves dropped during
the growth of the clover for seed are found, and wherein root-fibres are
more abundant than in the lower strata. The first six inches of soil, it
will be seen, contained in round numbers, 2-1/2 tons of nitrogen per
acre, that is, considerably more than was found in the same section of
the soil where the clover was mown twice for hay; showing plainly, that
during the ripening of the clover seed, the surface is much enriched by
the nitrogenous matter in the dropping leaves of the clover-plant.

"_Clover-roots_.--The roots from one square foot of this soil, freed
as much as possible from adhering soil, were dried at 212deg., and when
weighed and reduced to a fine powder, gave, on analysis, the following
results:

Organic matter[A] 64.76
Mineral matter[B] 35.24
-------
100.00
=======
[A] Containing nitrogen 1.702
Equal to ammonia 2.066
[B] Including clay and sand
(insoluble silicious matter) 26.04

"A square foot of this soil produced 582 grains of