COMMEMCIAL FERTILIZERS 523 



It should not be drilled in with the seed, as the action of 

 the chlorides in direct contact with the seed may injure 

 its viability. In addition to the potassium added to the 

 soil by kainit, there are also in this fertilizer magnesium 

 and sodium. The magnesium may be objectionable if 

 there is much already present in the soil (see par. 458). 

 Sodium may to some extent replace potassium in the soil 

 economy, and in that way may be beneficial. 



Silvinit contains its potassium both as chloride and as 

 sulfate. It also contains sodium and magnesium chlorides. 

 Potash constitutes about 16 per cent of the material. 

 Owing to the presence of chlorides, it has the same effect 

 on plants as has kainit. 



The commercial form of potassium chloride generally 

 contains about 80 per cent of potassium chloride or 50 

 per cent of potash. The impurities are largely sodium 

 chloride and insoluble mineral matter. The possible 

 injury to certain crops from the use of the chloride has 

 already been mentioned. For crops not so affected, potas- 

 sium chloride is a quickly acting and effective carrier of 

 potassium, and one of the cheapest forms. 



High-grade ' sulfate of potassium contains from 48 to 

 50 per cent of potash. Unlike the muriate it is not in- 

 jurious to crops, but is more expensive. 



There are a number of other Stassfurt salts, consisting 

 of mixtures of potassium, sodium, and magnesium in the 

 form of chlorides and sulfates. They are not so widely 

 used for fertilizers as are those mentioned above. 



442. Wood ashes. — For some time after the use of 

 fertilizers became an important farm practice, wood 

 ashes constituted a large proportion of the source of supply 

 of potassium. They also contain a considerable quantity 

 of lime and a small amount of phosphorus. The product 



