194: HANDY-BOOK OF HUSBANDRY. 



acid that they constantly throw off in respiration ; this the new 

 plant must get again from the air. A part has been resolved 

 into water, and has been thrown off from the lungs or skin, or 

 has evaporated in the escaping moisture of the manure ; this 

 must be taken by the new plant from the water of its sap. 

 Another part has been sold away in milk, wool, flesh, and bone ; 

 and this, (the part which demands the attention of the farmer,) 

 the new plant must take from the soil. 



If the crop of a field is fed to milch cows, and lOO lbs. of 

 phosphoric acid is sold away in the product, the manure must 

 contain lOO lbs. less of this necessary ingredient than the food 

 did, and if the whole of the manure is returned to the field, it 

 Still gets back lOO lbs. less than it gave. The next crop must 

 contain less phosphoric acid, — and so be smaller, — or it must take 

 a fresh supply from the soil. In time, the quantity in the soil, 

 however large it may have been at the outset, must be reduced 

 so low that the crop can take up, during its limited period of 

 growth, only a part of what it requires, and its quantity must shrink 

 in proportion to the decreasing supply. 



It may be in ten years, or it may be in a hundred, but the day 

 must inevitably come, when the constant removal of more than 

 is returned will lessen the ability of the soil to produce. 



This is the theory of the exhaustion of the soil, and it is based 

 on a law so simple, and yet so inexorable, that no man can deny 

 its existence, or reasonably hope to escape the penalty of its in- 

 fraction. The recuperative power of the soil is very great, and 

 we have many means for amending or postponing the injury o^ 

 excessive cropping ; but the use of green crops, fallows, thorough 

 and deep cultivation, exposure to frost, and the whole array of 

 processes through which we are provided relief, are only so many 

 means for more complete exhaustion in the end. 



To what extent it is advisable to increase the immediate fer- 

 tility of the soil, without the use of manure, must be decided by 

 each man according to his circumstances. Any process by which 

 this may be accomplished is a process of discounting future fer- 

 tility. No farm from which more of the earthy constituents of 



