28 COTTON 



form of superphosphate of lime. It can be used 

 alone, but is usually more effective if employed in 

 conjunction with potash and nitrogen manures. The 

 application of superphosphate is found to check 

 coarse growth, to encourage ripening, and to improve 

 greatly the quality of the fibre. A dressing of from 

 200 Ib. to 500 Ib. of this manure is applied per acre. 



Potassium is generally less urgently required than 

 nitrogen and phosphorus. It is of comparatively 

 little value if applied alone, but often produces bene- 

 ficial results when employed in combination with 

 phosphoric and nitrogenous manures. .It is usually 

 applied either in the form of kainit or of muriate of 

 potash, from 50 Ib. to 200 Ib. per acre being used. 



Rotation of Crops. The practice which prevails 

 in many places of planting cotton year after year 

 without intermission is very undesirable, since it 

 generally results in the gradual deterioration and 

 exhaustion of the soil, and consequently diminishes 

 the size and quality of the crop. Such exhaustion, 

 in most cases, however, is only temporary, and if the 

 land is allowed to lie fallow for a few years, it gradually 

 regains its fertility. The reasons underlying the 

 advantages which accrue from a system of rotation of 

 crops are not yet thoroughly understood, but it is 

 certain that much more is involved than the mere 

 withdrawal of the nutritive constituents from the soil, 

 and it is probable that a by no means unimportant 

 part is played by changes induced in the texture of 

 the soil, and by the activity of insects, fungi, and 

 bacteria, both hostile and friendly. 



In planning a rotation, it should be remembered 

 that different plants extract the constituents of the 

 soil in different proportions, and that whilst some 

 plants are provided with long roots and obtain their 

 food from the sub-soil, others have shallow, spreading 

 roots and procure their nourishment from the surface 

 layers. Other points to be considered are the effects 

 of the different crops on the growth of weeds and on 

 the presence of insects and other organisms. Bearing 

 these various factors in mind, it is evident that a crop 

 which has long, deeply penetrating roots, such as 



