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 >he 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 views 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 with 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. 



