214 



Fertilisers 



[PT. Ill 



Wheat, grain 

 ,, straw 



Barley, grain 

 straw 



Oats, grain 

 straw 



Hay 



Mangolds 



Swedes 



Potatoes 



Per 1 cwt. super- 

 phosphate or high 

 grade basic slag 



0-li bush. 

 ^5 cwt. 

 2-3 bush. 

 0-2 cwt. 

 1-3^ bush. 

 0-2 cwt. 



20 



20-40 



10 



Per 1 cwt. sulphate 



of ammonia or 

 nitrate of soda, or 

 1^ cwt. nitrohm 

 4J bush. 

 5 cwt. 

 6i bush. 



7 



6 



8-10 



32 



20 



20 



6^ cwt. 



bush, 

 cwt. 



The actual amount of the mixtures that may be used 

 is regulated by the following general rule : 



Additional manure usually gives extra crops (pro- 

 vided it is suitable) but beyond a certain point the yield 

 per cwt. of manure falls off, so that the extra crop is 

 obtained at higher cost per ton or per bushel than a 

 smaller crop would be. This is known as the Law of 

 Diminishing Returns, and it holds very generally; it is 

 just as true for the horse-power of a motor cycle as of 

 the yield of wheat. Table XIX gives an illustration 

 from the Broadbalk plots at Rothamsted: 



Table XIX. hifluence of increasing dressings of nitro- 

 genous manures on yield of wheat; Broadbalk field. 

 Average 61 years, 1852-1912 



(See Figs. 2 and 39. ) 



