1921.] Notes on Manures for December. 833 



Calcium carbonate (CaCO$) : Limestone, ground limestone, 

 chalk, ground shells, lime mud, chance mud, and other lime 

 wastes from factories. Some of the English limestones are 

 yery pure, running up to 90 or even 95 per cent, of purity, 

 100 lb. having the same value as 50-53 lb. of calcium oxide 

 (CaO). Fineness of grinding is an important consideration 

 here. The waste limes naturally vary considerably. 



Potassic Fertilisers and Crop Yields. — During the War 

 farmers had to do without much potassic fertiliser and many 

 of them suffered less than they expected. The idea arose in 

 some cases that perhaps potassic fertilisers are not as necessary 

 as had been thought. This, however, is not a correct deduc- 

 tion. The withholding of potash does not usually show 

 immediately on the crop; it produces its effects later. The 

 number of lb. of potash (K 2 0) removed from an acre of ground 

 are as follows : — 



K 2 removed (lb.). 





Yield 



In 



In 



Total. 



Equivalent to 





per acre. 



grain. 



air aw. 





sulphate of potasl 

 lb. per acre, 



Wheat 



36 bush. 



12 



24 



m 



67 



Barley 



40 „ 



10 



2P> 



3d 



67 



Oats 



50 p 



10 



42 



52 



96 



Clover hay 



2 tons 







84 



155 



Swedes 



u „ 



Roots 



only 



64 



11 ( J 



Mangolds 



30 „ 



>> 





300 



555 



Potatoes 



12 „ 



Tubers only 



153 



283 



Assuming that land is in fair condition to begin with a 

 farmer might go through a war rotation without much risk, 

 but if after that he has taken a potato crop he has probably 

 fairly heavily depleted the store of potash in the soil. Lack 

 of potash shows itself in a variety of ways, but when liberal 

 nitrogenous manuring is given a common indication is a 

 tendency to disease. Most good farmers are supplying nitro- 

 genous fertiliser more liberally than they used to do. Before 

 the War the total consumption in the United Kingdom of 

 sulphate of ammonia and nitrate of soda used to be 140,000 

 tons per annum; in 1920 it was 237,000 tons. If farmers 

 simultaneously reduce the consumption of potassic fertilisers 

 they run the risk of inducing undesirable effects such as lack 

 of vigour in their crops. This point has been definitely tested 

 with a glasshouse crop. Dr. W. F. Bewley showed at the 

 Cheshunt Experimental Station that the number of tomato 

 plants affected by the " stripe disease " was, out of a total 

 of 120 in each plot : — 



B 



