8 MASSACHUSETTS AGRICULTURE. 



tion they occur in different forms of vegetable life. It remains, 

 then, to ascertain what elements a given soil contains, and in 

 what proportion, and we are ready to apply our principle. 

 Let the elements of fertility contained in a given soil be rep- 

 resented by the letters A, B, C. We plant, for instance, a 

 vegetable which contains the same elements as are represented 

 by C. The original soil contains A, plus B, plus C. At the 

 end of the year a certain amount of C is appropriated ; and by 

 the same process repeated a few successive years, C becomes 

 exhausted. 



It is evident, as the vegetable produced contains only C, 

 that A and B still remain in the soil. Then take another 

 vegetable, the constituents of which are represented by B. 

 That the product which called for the elements of fertility 

 denoted by C can no longer be grown is no reason why a crop 

 requiring B will not turn out as well as did the former the 

 first season. And so we might go on until the sum-total of 

 the fertilizing elements denoted by A, B and C is exhausted, 

 and the soil is, in common phrase, run out. It is thus seen 

 that, under the conditions here supposed, a succession of 

 equally good crops is grown upon the same land, without any 

 addition of fertility. 



The vast economy effected in the productiveness of a given 

 piece of ground, by the observance of this rule, becomes 

 apparent upon the most cursory view. Old-time farming saw 

 necessity of fallowing where soil had ceased to be productive 

 of a given crop ; and this constant lying idle of some part 

 of the land is in reality just to what neglect of the principles 

 of rotation leads to-day. Many a farmer, year after year, by 

 preparing the same land for the same crop with an occasional 

 fallowing, goes on piling up wealth of fertilizing power, per- 

 haps only to be utilized by his more enlightened successor. 



Simple, however, as is this underlying principle of the 

 rotation of crops, it suggests problems most difficult of solu- 

 tion. It is easy to say, given the relative amount of fertiliz- 

 ing agents contained in a certain soil, determine the kind of 

 production to which it is adapted ; but it is not so easy to 

 ascertain either the elements contained, or the best combina- 

 tion of those elements, to forward as well as to insure vegetable 

 growth. We all know that different forms of food, which 



