1834.] Scientific Intelligence. 147 



XI. —European Science. 

 De Candolle's Theory of the Rotation of Crops. 



It is a well-established fact in the practice of husbandry, that a succession of 

 the same kind of crops on the same piece of ground, deteriorates not only the 

 ground, but the crops. Thus, a successive crop of wheat, barley, or oats, on the 

 same land, destroys the stamina of the ground, and renders each succeeding crop 

 less in produce and value. A succession of wheat, barley, and oats, frequently 

 repeated, will produce the same effect, though not so quickly. Even a succession 

 of green crops will affect both the crops and the soil in a similar manner, in a 

 given time. 



This deterioration of soil and crop, is most perceptible when there is no inter- 

 mediate application of manure. Manure will, no doubt, protract the period of 

 greatest deterioration ; but manure cannot constantly maintain a profitable re- 

 turn from a succession of the same kind of crop. Besides, it is impossible to ob- 

 tain a sufficient quantity of manure for frequent intermediate applications, in 

 order to counteract all the effects of deterioration. The impossibility of main- 

 taining to perfection the same kind of vegetable on the same piece of ground in a 

 well cultivated garden, illustrates, in a striking manner, the limited powers of 

 manure. In the field, where the cereal crops always ripen their seed, the power 

 of manure is still more limited. These evil effects, arising from what is em- 

 phatically and properly called over-cropping, have, therefore, been established 

 beyond doubt. 



To obviate the serious evil of deterioration of soil and crop, which neither labour 

 merely, however dexterous, nor manure, however well prepared, can prevent, the 

 adoption of a succession of different kinds of crops has been attended with bene- 

 ficial results. Tims a green crop, such as grass, turnips, or potatoes, was made 

 to succeed a corn crop ; and when this alternation of crops was substituted for a 

 successive series of corn or grain-crops, experience soon discovered that less de- 

 terioration affected any crop of the series, or the land itself. It was also found, 

 by this arrangement, that a longer period might elapse, than by the former, be- 

 tween the applications of manure, without diminishing the gross produce of the 

 intermediate crops. 



In the progress of experience, this beneficial arrangement of cropping was dis- 

 covered not to bestow all the advantages of which the alternate system was capable. 

 It was well to cause the gentler sway of the green crop to succeed the severer energies 

 of a corn one ; but it left the important question undecided, whether the particu- 

 lar corn crop selected was the most proper one by nature to follow its predecessor. 

 Thus, it would be an improvement on the old series of cropping, to make wheat 

 follow grass, barley after potatoes, and oats succeed turnips ; but is wheat the 

 best successor to grass of any of the corn crops ? and, in like manner, a similar 

 question might be asked of the rest of the series. Experience again suggested, 

 that a better arrangement might be followed. It said, let wheat follow a bare fal- 

 low, potatoes, or beans ; let barley succeed the turnip, and let oats be taken after 

 the grass. 



The trials of experience suggested yet better arrangements, to secure the great- 

 est produce of the different kinds of crops. It was soon discovered that all kinds 

 of soils were not adapted to the most luxuriant growth of all the kinds of crops. 

 Thus a clay soil was found to suit wheat better than barley ; a bare fallow better 

 than turnips ; and beans better than potatoes. A gravelly soil on the other hand, 

 was most suited to those crops which were rejected by the clay soil. 



