ROTATION OF CROPS. 985 



existing in the soil, and the removal ot" these matters by other 

 crops, which are sold away, must inevitably lessen the total amount 

 of them contained in the soil. 



The fact that within a few years, or even within a few genera- 

 tions, their supply may not be reduced to so low a point as to 

 prevent the cultivation of valuable crops is no argument in favor 

 of a blind dependence upon them. As surely as two and two 

 make four, and two taken from four leave only two to be taken 

 again, just so surely will it, sooner or later, be found that from 

 a given, (limited,) quantity of phosphoric acid in the soil, a yearly 

 quantity cannot be taken without reducing the amount that is 

 left. And if, by the growth of clover, we succeed in hunting out 

 the last hiding-place of an atom of phosphoric acid, and placing it 

 within the reach of a crop of wheat that is to be sold, we shall 

 render the ultimate exhaustion of the soil complete ; whereas, by 

 a judicious return of what is taken away, we might make most 

 valuable and repeated use of the soil's constituents. If we depend 

 upon it alone and return nothing but what it contains, we shall 

 finallv reach a point where not even clover, where no crop can 

 be grown, and from which it will be impossible to regain fertility 

 without the expenditure of more money than the land would be 

 worth, 



I should be glad if I could add to the completeness of this book 

 by specifving certain rotations as being the best to adopt under 

 certain circumstances, and I have tried hard in an examination of 

 the rotations followed in different regions to do this. But the re- 

 sult of my investigations has been simply to convince me that 

 there are so many circumstances of soil, climate, locality, market, 

 home supply, and need of selling crops in order to get money for 

 special uses, and, after all, so much to be left to the fancy or 

 whim of the farmer, that it is not safe to do more than to state 

 general principles, which bear equally on all cases, and, in view 

 of which, each cultivator should select for himself, after due con- 

 sideration, the system of cultivation that it will be best for him to 

 adhere to. 



This selection, however, should not he made without such con- 



