CH. ix] Effects on Crop Production 159 



Kelp has also been examined and also certain natural 

 deposits in the Western States. From one source or 

 another no less than 32,000 tons of potash (KgO) was 

 produced in the States in 1918. 



Certain minerals, notably feldspar, phonolite, etc., 

 have been suggested as fertilisers, but they proved in- 

 effective in trials made at Woburn. Biotite and nephelin 

 were more successful in Prianischnikow's experiments. 



It is only since the "sixties" that the Stassfurt 

 salts have been on the market, but the demand grew 

 so rapidly since 1900 that nearly 10 million tons per 

 annum of the crude salts representing approximately 

 one million tons of K2O were sold before the war, 

 mainly for agriculture. Three salts were in common use 

 here: sulphate of potash, muriate of potash, and kainit. 

 The Alsatian deposits occur in the plain north of Mul- 

 house ; they are estimated at 300 million tons of salts 

 containing on an average 22 per cent. KgO^. 



Potash is particularly needed for certain special crops 

 like mangolds (Figs. 32 and 33), potatoes and flax; in- 

 deed in this country it is usually associated with dairy 

 and potato farming. A usual dressing is 2 cwt. of 

 muriate or sulphate of potash for potatoes or 4 cwt. of 

 kainit for mangolds. Also, it is often effective on grass 

 land, especially on thin soUs, and on leguminous crops. 

 It may be needed for other crops as the standard of 

 farming rises and the yields are forced up : the natural 

 supplies of potash in the soil are not always sufficient 

 for the higher crops that ought to be obtained. Thus 

 on the Rothamsted barley plots phosphates give a con- 



^ The Stassfurt deposits are described in The Potash Salts, their Pro- 

 duction and Application, Dr Groth, Lombard Press, Londoji, and the 

 Alsatian deposits in Journ. Soc. Chem. Ind. 1918, xxxvn. 291 T. 



