Manures and Manuring 159 



soil. It would, however, be unwise to apply kainit to a soil carrying grow- 

 ing crops, as the salt and other impurities are likely to injure the tender 

 rootlets. 



The best time to apply kainit is a few weeks before the crop is to be 

 sown or planted. The salt in it, being readily soluble, will be washed down 

 into the soil out of reach of the roots, and the potash will be left behind 

 evenly distributed amongst the soil particles. From 2 to 4 cwt. per acre 

 is a fair dressing for kainit. 



Muriate of Potash. This is another name for a more or less impure 

 chloride of potassium. It is manufactured from carnallite, which is found 

 in enormous quantities in the German potash deposits. It contains from 

 70 to 98 per cent of pure potassium chloride, and its chief impurity is 

 common salt, which may vary from a mere trace to 20 per cent. Small 

 quantities of magnesium chloride and magnesium sulphate are also present. 

 The standard commercial muriate of potash usually contains 80 per cent 

 of pure potassium chloride, which is equivalent to 50'5 per cent of potash. 

 One ton of "muriate" thus contains as much potash as 4 tons of kainit. 

 In practice it may be used in the same way as kainit, but only one-fourth 

 of the quantity is needed about 56 to 112 Ib. per acre. 



Sulphate of Potash. This is a whitish crystalline salt manufactured 

 from natural deposits in the German potash mines. As a manure, the best 

 samples contain 98 per cent of sulphate of potash, equal to over 52 per cent 

 of pure potash. Inferior samples contain about 90 per cent of sulphate 

 of potash, equal to 48 per cent of pure potash. The double sulphate of 

 potash magnesia, which contains a good deal of magnesium sulphate, is 

 often called sulphate of potash, but it is inferior in potassic value. It 

 contains about 50 per cent of sulphate of potash, equal to 27 per cent of 

 pure potash. 



Sulphate of potash has gained a great name as a potato manure. It 

 is considered to produce tubers of better quality, but this would depend 

 largely upon the character of the soil. 



7. CALCAREOUS MANURES 



These are of a most important nature, and consist of lime in some 

 form, such as quicklime, slaked lime, chalk, marl, gas lime, and lime 

 shells. Lime is not only an essential plant food (see p. 108), but it plays 

 an important part in the generation and activity of bacteria in the soil, 

 and must be present to ensure fertility. Some soils are naturally of a 

 calcareous nature, while others may be deficient. In a fertile soil it has 

 been estimated that there are about 120,000 Ib. of lime to the acre, but 

 the quantity is very much less in others. In the Broadbalk Field at 

 Rothamsted, which had not been manured for fifty years, as much as 

 62,250 Ib. of lime is given for an acre of ground. 



Since the advent of so many chemical manures the ancient practice 



