FERTILIZERS. 
243 
wanting, its failure is readily accounted for on this supposition. If a soil is destitute of lime 
and potash, the addition of calcareous matter will not restore fertility, and the effect would be 
imperceptible. Facts seem to prove that the soil of Long-Island is destitute of the alkalies 
particularly potash ; on this view of the matter, the failure of gypsum is rationally accounted for. 
Time when gypsum may be laid upon the soil. Experience proves that the spring is the 
most favorable period. It may be sown upon a soil after or before the seed is sown ; or it 
may be sown upon the crop after it has appeared above the soil : the weather should be dry, 
but many prefer to sow it just before a rain. It is applied directly to hoed crops, as potatoes 
and maize. To render gypsum useful to wheat, it is never applied directly, but to a clover 
crop which precedes the wheat. It is, therefore, apparently indirectly, but really directly use¬ 
ful to wheat. Clover, as I have before observed, is both a lime and potash plant, but plaster 
is particularly beneficial to clover; it is a fact supported by observation. The clover in this 
way furnishes the potash which the wheat requires, and which it does not seem capable of 
doing itself, directly ; it is constitutionally impossible for wheat to get a supply of potash, 
except in newer grounds, without artificial aid. Phosphoric acid is another substance which 
clover furnishes, and is made available to the wheat crop which is to succeed it. 
The increased products arising from the use of gypsum, have been repeatedly determined by 
direct experiment. Allowing for the variablity of the seasons, or the liability to partial failures 
from drought, it has been shown that plaster, in an ordinarily favorable season, increases the 
product to twice its amount. This increase, however, holds good only in the case of clovers— 
the white and red. Admitting that the increase is less, the use of gypsum is still important. 
The influence of gypsum is not entirely dependent upon the rains of the season, inasmuch as it 
has often been observed that where clover appeared feeble, and plaster has been applied, the 
good effects of it have preceded the fall of rain. No doubt the evening dews were sufficient to 
dissolve and furnish plaster to the roots of the growing plant. While the general effects of 
plaster have been acknowledged, there is, and has been, a want of unanimity in regard to its 
mode of operating; or different views have been taken of its action. Of these view's only 
three appear to be important, and indeed it will not be absurd, even if we choose to maintain 
that each and all of them are right. Sir Humphrey Davy maintained that gypsum entered 
into the constitution of the plant, or its tissues, or is an essential substance in the chemical 
constitution ; hence it becomes, according to this view, an aliment in itself, and in its own in¬ 
tegrity, without undergoing decomposition. Liebig maintains, on the contrary, that its effects 
are indirectly obtained; that it first absorbs carbonate of ammonia from the atmosphere, which 
it fixes, undergoing at the same time decomposition itself, by losing its sulphuric acid, which 
goes to the ammonia, and forms w'ith it sulphate of ammonia. Experiments conducted under 
favorable circumstances, prove the chemical changes which Liebig asserts. Gypsum in a stable 
removes at once the smell of ammonia; and analysis of it subseqently proves the changes it 
has undergone. Boussingault is inclined to take a third view of the question, and maintain 
that clover and other plants, whose growth is so much promoted by gypsum, obtain sulphur 
from and by decomposition. Now, to a certain extent, each view is undoubtedly correct. 
