336 SYSTEMS OF MANURING CROPS [chap. 



the land — tobacco, cotton, and to a less extent sugar 

 cane — which most require manuring ; really perennial 

 crops like tea and coffee require much less manure and 

 that of a more slowly acting kind. It is only the short- 

 period crops which will respond properly to active 

 sources of nitrogen like nitrate of soda or sulphate of 

 ammonia. 



The incidence of rainfall must be closely studied. 

 No manure can be effective when the soil is either dry 

 or waterlogged ; and as the nitrogenous manures cannot 

 be expected to persist very long in the soil, their applica- 

 tion should be timed so as to be followed by a period of 

 growth with neither excessive rain nor a dry soil. 



Sugar cane. — A large number of experiments have 

 been conducted with sugar cane, and, though the results 

 naturally vary in the different countries, certain general 

 conclusions can be drawn. Before planting, a compara- 

 tively slow acting nitrogenous fertiliser should be used, 

 either the equivalent of farmyard manure or some seed 

 residue like castor pomace, to supply about lOO lb. of 

 nitrogen per acre. For the rattoon growths more active 

 forms of nitrogen are desirable — either sulphate of 

 ammonia or nitrate of soda supplying 50 lb. of nitrogen 

 per acre ; which of the two will prove the more suitable 

 depends upon the soil. Excess of nitrogen must be 

 avoided, as it induces late cane and an impure juice. 

 On many soils applications of potash salts (sulphate 

 of potash is generally the most economical form) are 

 very effective. Phosphates are less needed, though 

 superphosphate is often valuable on black alluvial soils. 



Cotton. — Cotton responds freely to fertilisers, and 

 there is evidence that the fertiliser should be a mixed 

 one but mainly phosphatic. About 4 cwts. per acre 

 of superphosphate and 2 cwts. per acre of cotton 

 seed meal or some equivalent organic source of 



