18 



IV. The Prece])ts of Practical Wi-iters. 



The points advanced by practical writers as Thaer, Low, Stephens and Rham, as the 

 principles of rotations are of considerable moment, especially in the field, but are no more than 

 sm-mises for the most part. They may be resolved into the three following assertions and precepts : 



1. That each plant requires a particular food and should therefore be repeated at as long 

 intervals as possible. 



2. That seed crops being peculiarly exhausting are to be interchanged with green or forage 

 crops and roots. 



3. That plants which require hoe tillage, being cleaning crops, should follow those which are 

 sown broadcast and encom-age weeds. 



In these positions we recognize the imperfect observations of farmers ; each one is true within 

 certain limits, and excepting the last, Avhicli is only a practical expedient, it is impossible through 

 them to reach any general principle. That each plant requires a particular food is an assertion 

 merely which, so far from carrying conviction, is altogether denied by some practical men and, 

 whether true or false, is beyond the means of these writers to prove. The second assertion, that 

 seed crops are exhausting, is sustained by experience ; but in what way they are exhausting is not 

 stated, and without this information the assertion is of little value. As we have remarked, the third 

 position is a practical expedient only, because both seed and forage plants may be hoed crops, as 

 corn, beans, cotton — tobacco, turnips, cabbages. 



Hence the precepts of practical writers resolve themselves into the two points, that the same 

 and allied species should be cultivated at as long intervals as expedient and that seed plants are to 

 be as seldom introduced as possible. Both these positions are of practical value, but they do not 

 merely labor under the defect of conveying no precise information, but may be used in forming 

 schemes of rotation of no economy whatever. Thus the following plan is perfectly conformable 

 with these precepts, but very objectionable. 



Manure, corn, tobacco, oats with clover, wheat, beans. 



or, as in the rotation for clay lands, by Mr. Rham, 



Manure, roots, oats with clover, beans, wheat. 



In the first a seed crop is followed by a foliage crop, but both of these are exhausting ; in 

 the second, beans are succeeded by wheat, both exhausting, but — and this is the imperfection of 

 such arbitrary precepts — ^the exhaustion in every case is not of the same kind or degree. We 

 are informed that certain crops are exhausting, but not of what ; they impoverish the earth, yet we 



