INORGANIC ELEMENTS OF MANURES AND CROPS. 373 



ported should not leave the dung-hill with less than that constant 

 quantity of mineral substance which it ought to contain. A crop 

 whicli abstracts from the ground a notable proportion of one of its 

 mineral elements, should not be repeatedly introduced in the course 

 of a rotation, which depends on a given dose of manure, unless by 

 the effect of time mineral element has been accumulated in the land. 

 A clover crop takes up, for example, 77 lbs. of alkali per acre. It 

 the fodder is consumed on the spot, the greater portion of the potash 

 and soda will return to the manure after passing through the cattle, 

 and the land eventually recover nearly the whole of the alkali. It 

 will be quite otherwise if the fodder is taken to market ; and it is to 

 these repeated exportations of the produce of artificial meadows 

 that the failure of trefoil, now observed in soils which have long 

 yielded abundantly* is undoubtedly due. Accordingly, a means has 

 been proposed of restoring to these lands their reproductive power, 

 by applying alkaline manure.* If under such circumstances carbo- 

 nate of soda would act as favorably as carbonate of potash or wood- 

 ashes, the soda salt, in spite of its commercial value, might prove 

 serviceable, and deserves a trial. 



The lime manures naturally promote the growth of plants of 

 which calcareous salts form a constituent ; but here a capital distinc- 

 tion must be made. A soil may contain from 15 to 20 in the 100 of 

 lime, and still be unable to dispense with calcareous manure ; be- 

 cause the lime is in some other state than as it exists in chalk, as 

 in the rubbish of pyroxene, mica, serpentine, and the like. A soil 

 of this kind, although replete with lime, might still require gypsum 

 for artificial meadow, and chalk for wheat and oats. It is from the 

 carbonate that plants of rapid growth derive the lime essential to 

 them, as was established by the researches of Rigaud de Lille, re- 

 searches which have been censured by agricultural writers to whom 

 they were unintelligible. I advocate the opinion of Rigaud, be- 

 cause in the Andes of Riobamba I have seen lucern growing in au- 

 gitic rubbish, very rich in calcareous matter, and yet greatly bene- 

 fited by liming. 



The operation of gypsum is to introduce calcareous matter into 

 plants. This I have endeavored to demonstrate from the analysis 

 of the ash on the one hand, and on the other, from the consideration 

 that finely divided carbonate of lime, as it exists in wood-ashes, acts 

 with equal efficacy upon artificial meadows. By what means gyp- 

 sum, if it does not enter the vegetable as a sulphate, parts with its 

 sulphuric acid, is at present conjectural. It appears highly proba- 

 ble that calcareous matter is chiefly beneficial from the particular 

 action it exercises on the fixed ammoniacal salts of the manure, 

 transforming these successively, slowly, and as they may be wanted, 

 into carbonate of ammonia. In the most favorable condition, the 

 earth is only moist, not soaked with water, but permeable to the air. 

 New researches will perhaps illustrate the utility of ammoniacal va- 

 pors thus developed in a confined atmosphere, where the roots are 



* Information communicated by M. Schattenmann. 

 32 



