CHAPTER VIII. 



THE MODE OP OPERATION BY WHICH CALCAREOUS EARTH IN- 

 CREASES THE FERTILITY AND PRODUCTIVENESS OF SOILS. 



PROPOSITION 3. The fertilizing effects of calcareous earth are 

 chiefly produced by its power of neutralizing acids, and of com- 

 bining putrescent manures with soils } between which there would 

 otherwise be but little, if any, chemical attraction. 



PROPOSITION 4. Poor and acid soils cannot be improved durably ', 

 or profitably, by putrescent manures, without previously making 

 them calcareous, and thereby correcting the defect in their con- 

 stitution. 



It has already been made evident that the presence of calcareous 

 earth [in small proportion, or not in too great excess], in a natural 

 soil, causes great and durable fertility. But it still remains to be 

 determined, to what properties of this earth its peculiar fertilizing 

 effects are to be attributed. 



Chemistry has taught that silicious earth, in any state of divi- 

 sion, attracts but slightly, if at all, any of the parts of putrescent 

 animal and vegetable matters.* But even if any slight attraction 

 really exists when this earth is minutely divided for experiment in 

 the laboratory of the chemist, it cannot be exerted by silicious 

 sand in the usual form in which nature gives it to soils ; that is, 

 in particles comparatively coarse, loose, and open, and yet each 

 particle impenetrable to any liquid, or gaseous fluid, that might be 

 passing through the vacancies. Hence, silicious earth can have 

 no power, chemical or mechanical, either to attract enriching 

 manures, or to preserve them when actually placed in contact and 

 intermixed with them ; and soils in which the qualities of this 

 earth greatly predominate, must give out freely all enriching mat- 

 ters which they may have received, not only to a growing crop, but 

 to the sun, air, and water, so as soon to lose the whole. No por- 

 tion of putrescent matter can remain longer than the completion 

 of its decomposition j and if not arrested during this process, by 

 the roots of living plants, all will escape in the form of gas (the 

 latest products of decomposition), into the air, without leaving a 

 trace of lasting improvement. With a knowledge of these pro- 

 perties, we need not resort to the common opinion that manure is 



* Davy's Agr. Chem. page 129. 



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