Clover as a Preparatory Croj) for Wheat. 
413 
let, 6 inches. 2ud, 6 inches. 3i J. 6 Inches. 
Moisture 17-1I) .... 18-24 .... lG-(i2 
Phosphoric acid -198 .... -109 .... -143 
Nitrogen -134 .... -07.5 .... -053 
Equal to ammonia '162 .... -091 .... -004 
lbs. lbs. lbs. 
Weight of 1 foot square of soil .. (iO .. .. Gl .. .. G3 
Calculated per acre, the absolute weight of 1 acre of this land, 
6 inches deep, weighs : 
lbs. 
1st G inches 2,013,600 
2nd „ 2,057,160 
3nd „ .. .. 2,746,280 
No great error, therefore, will be made if we assume in the 
subsequent calculations that 6 inches of this soil weigh 2J millions 
oi pounds per acre. 
An acre of land, according to the preceding determinations, 
contains : — 
1st, 6 inches. 2nd, 6 inches. 3rd, 6 mches. 
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 6 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 in- 
sufficient for the production of a good corn-crop. However, 
when calculated to the acre, we find that 6 inches of surface soil, 
in an acre of land, actually contain over 2 tons of phosphoric acid. 
An average crop of wheat, assumed to be 25 bushels of grain, 
at 60 lbs. per bushel, and 3000 lbs. of straw, removes from the 
land on which it is grown 20 lbs. of phosphoric acid. The 
clover-soil, analysed by me, consequently contains an amount 
of phosphoric acid in a depth of only 6 inches, which is equal to 
that present in 247^ average crops of wheat ; or supposing that, 
by good cultivation and in favourable seasons, the average yield 
of wheat could be doubled, and 50 bushels of grain at 60 lbs. a 
bushel and 6000 lbs. of straw could be raised, 124 of such heavy 
wheat-crops would contain no more phosphoric acid than actually 
occurred in 6 inches of this clover-soil per acre. 
The mere presence of such an amount of phosphoi'ic acid in a 
soil, however, by no means proves its sufficiency for the produc- 
tion of so many crops of wheat ; for, in the first place, it cannot 
be shown that the whole of the phosphoric acid found by analysis 
occurs in the soil in a readily available combination : and, in 
the second place, it is quite certain that the root-fibres of the 
wheat-plant cannot reach and pick up, so to speak, every particle 
■of phosphoric acid, even supposing it to occur in the soil in a 
form most conducive to " ready assimilation by the plant." 
