CHAPTER VI 



THE POTASSIC FERTILISERS 



Early Use of Wood Ashes — The Stassfurt Deposits — Manufacture 

 and Composition of commercial Potash Fertilisers — The 

 Retention of Potash by the Soil — The Function of Potash in 

 the Nutrition of the Plant — Dependence of Carbohydrate 

 Formation upon Potash, as illustrated in the Barley and Man- 

 gold Crops — The Action of Nitrate of Soda upon insoluble 

 Potash Compounds in the Soil — Potash Fertilisers as promot- 

 ing the Growth of Leguminous Plants— Efifects of Potash 

 Starvation upon Vegetation — Potash as a Preventive of 

 Fungoid Disease — Potash as prolonging the Growth of the 

 Plant— Destruction of the Tilth of Clay Soils by Potash Salts 

 — Soils deficient in Potash. 



Although the water cultures already described, 

 coupled with the results of the Rothamsted experiments 

 even in their early years, showed that of the alkali 

 metals found in the plant's ash only potassium was 

 indispensable, for a long time the salts of potash could 

 not be obtained in quantities or at a price appropriate 

 to agricultural requirements. Almost the only source 

 of potash was the crude carbonate or " potashes," which 

 was obtained by dissolving the soluble salts found in 

 wood ashes ; and though this was to a small extent 

 supplemented by the nitrate of potash or saltpetre 

 obtained from India, and by a certain amount of 

 sulphate of potash obtained from " kelp " — the ashes of 

 seaweed — no widespread use could be made of potash 



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