ROTATION OF CROPS. 109 



follow rotation. It is very evident that wheat leaves the soil in a better condition for corn 

 than it does for wheat again, and corn leaves it better for wheat. Clover, peas, and sweet 

 potatoes are among the best crops for preparing or leaving the ground for any crop. Wheat 

 does much better after Irish potatoes and tobacco in some States, than after any other grain 

 or vegetable. 



Several instances have come under my observation where sweet potatoes were raised for 

 10 to 20 years in succession, without any apparent exhaustion, but with great fertility to the 

 soil. In looking into the chemistry of this subject, we find in the analyses that wheat con 

 tains about 55 per cent, of starch, and corn 70 per cent. The gluten in the former runs from 

 10 to 19 per cent., while in the latter it is about 12 per cent. Now if the soil contains a cer 

 tain average supply of these and other inorganic substances upon which the plant feeds, and 

 the same wheat or corn crop is grown in the same soil year after year, the crops will carry off 

 some of these substances in a greater proportion than others, so that they will become rela 

 tively less every season. The result is, the soil will become so impoverished of &quot;these sub 

 stances that no crop of the same kind can be raised, although it may contain a large store of 

 other inorganic substances. When these crops are grown one after the other, one draws 

 especially upon one class of elements and the other upon another, thus keeping up the equi 

 librium of fertility necessary to support either plant. 



In connection with these operations there must be two kinds of exhaustion general and 

 special the former consisting of gradual extraction of all the essential elements upon which 

 each crop feeds, and the latter consisting of a want of one or more of these elements.&quot; 



There evidently are other reasons for the difference, in connection with the many theories 

 advanced, which are not yet understood, and which are not necessary for the farmer to under 

 stand, since he has to deal with the fact itself, and its relations to agriculture. He can afford 

 to leave the explanation of this phenomenon to the agricultural chemists, and give his atten 

 tion to the benefits that may be derived from a knowledge of the facts. We find that 



Nature Generally Follows a Course of Rotation in her various departments of 

 vegetable production. Although mowing lands part with their annual crop of hay, and by a 

 partial rest, or a pasturage of their aftermath or &quot; rowen,&quot; will remain fresh and seem to 

 retain the original plants that produced the crop, yet on a close examination it will be ascer 

 tained that the varieties of the grasses and other plants will change gradually from year to 

 year, some kinds predominating at one time and others at another, in a continuous round of 

 rotation. 



But this fact of change is more strikingly illustrated in the succession of forest trees, 

 which cannot fail to attract the attention of even the most casual observer. &quot;We distinctly 

 recall, among our childhood memories, a grand old forest of oak, walnut, and chestnut. Many 

 of these monarchs of the forest succumbed to the fate of the woodman s axe. Soon appeared 

 in their places a thick growth of white pine, which increased with remarkable rapidity. 

 These pines were subsequently cut down, and maple, chestnut, and oak came up with scarcely 

 a pine tree among them. And thus it is always found that when a forest is cut down, and 

 the roots destroyed, another growth of trees succeeds of an entirely different nature, and 

 these are followed by still another variety, completing in time a rotation all probably pro 

 duced from seeds that may have lain dormant in the soil for centuries, waiting for favoring 

 conditions to germinate. 



It is often found that when a soil becomes exhausted to a certain extent by one particu 

 lar crop, and ceases to give a sufficient return of it, it will still yield a large crop of some 

 other kind that is adapted to it, and which calls for just the elements of plant growth that 

 this soil may contain ; this is not only a fact concerning field crops, but the same is true of 

 gardening, and the culture of trees, etc. There would be found few gardeners of experience, 

 if any, who would think of cultivating cabbages, turnips, or peas, on the same piece of land 



