LIMING. 303 



CHAPTER VI. 



OF MINERAL MANURES OR STIMULANTS. 



At.i the organic manures, when burned, leave ashes composed of 

 earthy and sahne substances. The action of these substances upon 

 vegetation is quite unquestionable, and it is certain that an organic 

 manure, were it ever so rich in azotized principles, and ever so as- 

 similable, would still be imperfect did it not further contain the truly- 

 mineral matters which plants require to meet with in the soil, in 

 order to complete their growth and bring their seeds to maturity. 

 The most active organic manures are always abundantly provided 

 with inorganic principles. Farm dung (dry) contains about one- 

 fourth of its weight of such substances, and the water which is used 

 for irrigation invariably holds saline matter in solution. 



Nevertheless, repeated cropping will often end by depriving the 

 soil of the mineral substances which plants require ; the salts con- 

 tained in the manure supplied are sometimes inadequate to meet 

 the demands of successive crops, and then the return falls off. It 

 IS consequently necessary in certain cases to furnish the soil anew 

 with saline matters, in order to supply the continued drain that is 

 made upon it, or to meet the exigencies of particular crops which 

 are known to require an unusually large quantity of salts for their 

 successful cultivation. It is in this way that clover, lucern, and 

 sainfoin require plaster, (gypsum ;) the cereals, silica, and certain 

 calcareous salts ; the vine, potash, &c. 



Practice got the start of science in tlie application of mineral ma- 

 nures or stimulants. If their useful influence cannot be denied, as 

 it cannot, if the circumstances in which it is advantageous to admin- 

 ister them, if the conditions and the doses in which they ought to be 

 given to the ground have been the subject of long and careful obser- 

 vation with farmers, it must still be admitted that we are far from 

 understanding exactly in what way they act ; this is another motive 

 for continuing to study them with perseverance. 



CALCAREOUS MANURES. • 



In certain soils we have said that the calcareous element is either 

 wanting, or present in very small and inadequate quantity ; other 

 soils, again, abound in calcareous matter, and observation appears to 

 prove that the presence of carbonate of lime in a soil adds unequivo- 

 cally to its fertility. The majority of the good wheat lands hitherto 

 examined have been found to contain a notable quantity of this earth 

 or earthy salt. 



It is usual to put lime into the ground in the state of caustic or 

 quick-lime ; this is liming, properly so called. But it is also ap- 

 plied in the state of carbonate, as when we make use of chalk or 

 marl, or shell-sand from the sea-shore. 



