ROTATION OF CROPS. 209 



The facts regarding manures then, are, that permanent ones must consist of a combination of 

 organic and inorganic matters ; or, that the elements of organic matter must, in some way, be 

 combined with the inorganic. If fields are manured with inorganic matters, as leached ashes, 

 gypsum, etc. those fields in time cease to be fertile. Thus the farmers of Long-Island, who 

 have been in the habit of using leached ashes for a few years, find that the effects at first are 

 quite decided, yet soon they begin to decline, and after a while cease to exert a favorable 

 influence upon vegetation. There seem to be, in facts of this kind, a distant analogy in the nu- 

 triment of plants and animals : a change of diet may be required in both kingdoms ; the ap- 

 petite in animals indicates this in the animal, and the general eifects of one nutriment, long 

 continued, indicates it in the vegetable kingdom. Dogs when fed upon gelatine alone, soon 

 lose their appetite, and, if persisted in as food, they will starve upon it. Yet gelatine and 

 starch, under some conditions, is nutritious, and, for convalescents from fever, is one of the 

 safest kinds of nutriment, and one upon which the system is known to thrive, and gain flesh 

 and strength. Combination of elements, and a change also of the compounded matters, are 

 required by both classes of organized bodies. We find the organic elements in all cases in 

 the ash of the organs, both of animals and vegetables. It is true some of the lowest forms of 

 vegetation, as the mucors or moulds, according to Mulder, leave no ash or residue on being 

 burnt. These may, and must be, however, regarded as mere exceptions to a general law. 

 Those who feed animals for market know well that a change of diet is necessary to bring them 

 to the highest state of perfection. The natural rotation of crops is a fact which points to the 

 same principle. Experience then, and observation, agree in sustaining this important principle 

 of cultivation and of feeding. The dictation of an appetite, in the case of animals, should be 

 heeded ; and the deterioration of vegetables, when fed with a single nutritive element, should 

 also warn us that a change of treatment and diet is called for. 



ROTATION OF CROPS. 



A rotation of crops, as a means for increasing the products, has been regarded as one of the 

 means for sustaining and prolonging the fertility of the soil. What is the foundation of a 

 practice so general and so much approved by practical men ? Observation has brought to light 

 the fact that no crop can be sustained, for a long period, on the same area. This fact is not 

 disproved by another — that there are spots of great fertility, and abounding in nutriment^ which 

 is stored up in the soil : some of the western bottoms on the Ohio and Mississippi are ex- 

 ceedingly productive for years, even in Indian corn. These spots contain a great abundance- 

 of all the elements of nutrition required by the plant : but this is the case with very limited 

 areas only ; the greater part of the earth's surface has, at any one time, but a small amount of 

 the essential food of plants in a condition fit for the nourishment of vegetables. 



When we find, therefore, that a crop begins to be less vigorous and productive, after culti- 

 vation on the same field, we may conclude that it has exhausted one or more of the essential 

 elements of nutrition. Now, although this same plant, or crop, may not thrive, still experience 



{ACKICCLTUBAL RePOKT — VoL. III.] 27 



