200 CHEMICAL FERTILIZERS 



manure, labour and risk of injury from insect pests and 

 fungoid diseases. In addition to the disadvantages of con- 

 tinuous cultivation as regards cost of labour and suscepti- 

 bility to disease, there are also many advantages in crop 

 rotations owing to the different habits of plants in their 

 root systems and in the kinds of fertilizing materials which 

 they extract from the soil. The bacterial condition of a 

 soil is also much modified by the different phases of the 

 rotation, whilst the continuous repetition of one species limits 

 the variety of bacterial flora. Rotations of crops, intended 

 to produce the largest profits, must vary widely according 

 to the conditions under which farming is practised in the 

 different localities, though there are certain guiding principles 

 which ought not to be lost sight of. 



Climate is always a very important consideration when 

 deciding the kind of crop to be grown. Rainfall, exposure 

 to winds and range of temperature have a great influence 

 on the system of farming. The important mangold crop, 

 for example, gives very high yields in the southern counties 

 of England, but only moderate crops are grown on the 

 best soils in the northern counties, and less would be 

 grown there if yield was the only consideration. A small 

 quantity of mangolds is very convenient on a farm, since 

 they keep well over the winter and are available at a time when 

 the softer turnips and swedes have become exhausted. In 

 the cool and damp climates of the more northern parts of 

 the British Isles, wheat takes longer to ripen than in the 

 southern counties, and very much longer than in the sunny 

 climate of Southern France. The long days of Northern 

 Canada permit continuous growth with a corresponding 

 diminution in the number of days from seed time to harvest. 

 The result of this delayed ripening in the British Isles is a 

 softer and inferior wheat of greater water content and lower 

 milling value. Great improvements have taken place in 

 varieties of wheat during recent years, so that we may hope 

 that some of this inferiority of British wheat may pass away. 

 Oats and turnips flourish in cool and moist climates, and are 

 therefore particularly suited to the western parts of the 



