594 THE HOME, FARM AND BUSINESS CYCLOPAEDIA. 



Rye-grass is not a good preparation for wheat, and two white straw crops 

 are not, as a rule, likely to succeed. Red clover refuses to grow after a 

 previous crop or crops of the same plant, and it is well known that pota- 

 toes and turnips may be grown too frequently on the same field. This may 

 be best explained upon the theory of rivalry for similar food constituents. 

 De Candolle, the eminent French botanist, advanced the theory of root- 

 excretions, to account for the difficulty of growing certain plants in suc- 

 cession, but the latest investigations upon this subject have yielded only 

 negative results. 



5. Besides the foregoing scientific reasons for varying the cropping of 

 6 elds and following a well-devised rotation, there are several practical 

 considerations which confirm their usefulness. (1) they promote cleanli- 

 ness or freedom from weeds ; (2.) They give a continuous supply of food 

 for stock, as well as grain for man ; (3) they divide the labour of the farm 

 over the entire year ; (4) give a system to farming operations ; (5) and 

 diminish a farmer's risks. 



ABUSES OF ROTATIONS. They are, however, liable to abuse when un- 

 duly strained. No rotation can be suitable to all soils and to all conditions 

 of the market, and therefore, a degree of latitude should be allowed, espe- 

 cially upon large farms, where soils and climates vary. 



INFLUENCE OF SOIL IN DETERMINING ROTATIONS. The general out- 

 line of a rotation may be thus drawn : 



Fallow : grain.: forage : grain. 



The fallow may be naked or cropped, and the cropping of a fallow is ca- 

 pable of many modifications, according to the quality of the land. Simi- 

 larly the grain crops and forage crops will be selected according to the ca- 

 pabilities and adaptabilities of the soil. 



On the most retentive clays wheat and beans will be the predominating 

 cereals, and bare fallows relieved by the limited cultivation of rape, vetches 

 will constitute the fallow portion. 



On strong clay loams wheat and beans still hold their place, but the 

 fallow will be cropped with mangels and part swedes, in addition to the 

 crops cultivated on the stiffer clays. 



On loamy soils any crop is suitable a fact which makes them particu- 

 larly valuable. Potatoes may be mentioned as especially suitable for this 

 class. 



On sandy loams and sandy soils, white turnips are more suitable than 

 swedes in England, forage crops are very succesful, and these soils being 

 easily worked are kept constantly under crop, and require the consolidat- 



