The Rotation of Crops 



to sustain a crop. Obviously this mode of procedure is unprofitable 

 and tends of necessity to exhaustion, although it must be confessed 

 that utter exhaustion of any soil is a thing at present almost 

 unknown. But, instead of following a practice which impoverishes, 

 let us enrich the soil with manure, and change the crops on the 

 same plot, so that when one crop has largely taxed it for one class 

 of minerals, a different crop is grown which will tax it for another 

 class of minerals. Take for a moment's consideration one of the 

 necessary constituents of a fertile soil, common salt (chloride of 

 sodium). In the ash of a Cabbage there is about six per cent, of 

 this mineral, in the Turnip about ten per cent., in the Potato two to 

 three per cent., in the Beet eighteen to twenty per cent. On the 

 other hand the Beet contains very little sulphur, but both Turnip 

 and Beet agree in being strongly charged with potash and soda. It 

 follows that if we crop a piece of ground with Cabbage, and wish to 

 avoid the failure that may occur if we continue to crop with Cabbage, 

 we may expect to do well by giving the ground a dressing of common 

 salt and potash salts, and then crop it with Beet. 



The whole subject is not exhausted by this mode of viewing it, 

 for all the facts are not yet fully understood by the ablest of our 

 chemists and physiologists, and crops differ in their methods of 

 seeking nourishment. We might find two distinct plants nearly 

 agreeing in chemical constitution, and yet one might fail where the 

 other would succeed. Suppose, for instance, we have grown Cab- 

 bage and other surface-rooting crops until the soil begins to fail, 

 even then we might obtain from it a good crop of Parsnips or 

 Carrots, for the simple reason that these send their roots down to a 

 stratum that the Cabbage never reached ; and it is most instructive 

 to bear in mind that, although the Parsnip will grow on poor land, 

 and pay on land that has been badly tilled for years, yet the ashes 

 of the Parsnip contain thirty-six per cent, of potash, eleven per cent. 

 of lime, eighteen per cent, of phosphoric acid, six per cent, of sul- 

 phuric acid, three per cent, of phosphate of iron, and five per cent, 

 of common salt. How does the Parsnip obtain its mineral food 

 in a soil which for other crops appears to be exhausted ? Simply by 

 pushing down for it into a mine that has hitherto been but little 

 worked, though Cabbage might fail on the same plot because the 

 superficial stratum has been overtaxed. 



Having attempted a general, we now proceed to a particular 

 application. In the first place, good land, well tilled and abun- 

 dantly manured, cannot be soon exhausted; but even in this case 



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