244. . GEOLOGICAL SURVEY 
amount of potash; and clover, with all the pea tribe, and tobacco, require much lime. Plants thus 
constituted are obviously those that should succeed each other in a rotation. 
The following table from Liebig’s investigations will render this still more obvious. 
The crops given were found to abstract from 2.47 acres of land the quantity of salts in the table. 
Alkaline Salts. Salis of Lime and Silica. 
Magnesia. 
‘A crop of wheat, - - - 1203 Ibs, 784 lbs. 260 lbs. 
A crop of peas, - - - 198f “ Bye AG 
A crop of beets, without leaves, 361 “ 372 “ _ 
And the quantity of phosphates taken up are, 
Peas. Wheat. Beets. 
117 Ibs. 112 Ibs. 373 Ibs. 
Now from these numbers it is plain, that if any one of these plants. be cultivated in a soil that 
supplies annually an amount of these salts short of what the plant requires, there must be a failure 
of the crop. ‘Thus a soil that cannot afford a large annual amount of alkaline salts is unfavorable 
to the growth of the beet, at the-same time that both wheat and peas may grow quite well. Peas, 
it is evident, can only be raised where salts of lime and magnesia are abundant, while both wheat 
and beets may flourish. 
There is no want of silica in any soil, and seeing the large quantity of this taken up by wheat, 
one might naturally enough suppose it the least impoverishing of all crops, yet the reverse of this, is 
the fact, for it is well known that the grain crops are of all others the most exhausting. 
Bousingault, who unites the rare qualifications of a profound chemist, and practical agricultu- 
rist, and therefore whose deductions are entitled to the utmost confidence, has explained this, both 
by experiment in the laboratory, and in the farm on the large scale. 
He raised wheat on a soil deprived artificially of its nitrogen, and found that it only contained the 
amount of that gas that was in the seed, showing that it acquired none from the atmosphere, while 
peas raised under similar circumstances, contained much more nitrogen than the seed, proving that 
it took the surplus from the atmosphere. And thus it is that the grain crops exhaust, by deriving 
all their nitrogen from the soil. 
fis experiments on the large scale were as follows: 
Wheat was raised two successive years with manure, and one year of fallow, giving for the pro- 
duce 4318 kilogrammes of wheat and.7500 of straw per hectare, at an expense of 20,000 kilogrammes 
of manure. 'These when dried gave the following results. 
Wet. dry. Carbon. Hydro. Oxyg. Nitro. Ashes. 
Wiheats Zeta as 2836_- =. . 1087.4. -. 164-5. == 1230.8. --65.2.- 6821 
Sirawjes- a aa 5550Leec4 2686.2....294.2_. 2159.0. --22.2.. 388.5 
Notaleeeene sce. Sobran ee 3723.6. _.458.7_ --3389.8_ .-87.4_. 456.6 
Manure,. .--.----4140___._1482.1___173.9. -1068.1. .-82.8_ 1333.1 
Difference, ----__ 4246... Q2241.5...284.8. -.2321.7... 4.6... 876.5 
It appears from this table, that all the ingredients of the crop were greatly increased above those 
found in the manure, excepting the nitrogen, which is nearly equal in both. 'The carbon is nearly 
trebled, proving the truth of the theory that ascribes this constituent to the atmosphere. ‘The hydro- 
