t 574 1 



not be used as a top-dressing. The inferior kinds of salt 

 are better for manurial purpose. Neither Na nor Cl is essen- 

 tial for plant life, and Na with S (/. e. Na 2 SO 4 ) is therefore of 

 more value as a manure. Impure salt contains also Na- 

 2COs, NaNOs, KNOs and other substances which are also 

 useful as manure. NaCl has however an indirect manurial 

 action on the soil, especially on soil rich in lime. As gypsum 

 pushes out potash, magnesia and ammonia from the hydrous 

 double silicates, so also common salt replaces lime first and 

 then magnesia, potash and phosphoric acid. Wolff grew a 

 quantity of buckwheat upon a field one half of which was 

 manured heavily with common salt, while the other half was 

 left unmanured. On analysing the ashes of the buckwheat 

 straw, he found that the portion of the crop which had 

 received the salt contained less soda but more potash, than 

 the other. An application of common salt to the land might 

 thus exert a decided fertilizing action, by merely pushing out 

 lime and potash from the surface layers of the soil and 

 sending them down to where the roots of the crop are. 

 The disintegrating effect of lime and salt on rocks and soil 

 particles is of great importance in the formation of soils 

 and, the, growth of vegetation. 



956. Salt is injurious to leguminous crops generally. 

 To cereal crops it often does good, especially when there is 

 any tendency for a crop running to straw and producing 

 a small proportion of grain. It toughens the straw of cereals. 

 Chloride of magnesium and chloride of potassium have the 

 same effect of reducing the tendency of a crop running to 

 straw. Tobacco grown with salt as manure produces 

 tougher and more flexible leaves. Hemp produces a larger 

 amount of better fibre with salt used as manure. Potatoes 

 have a tendency to become waxy when salt is used as 

 manure. 



957. For cotton salt is a very useful manure on soils 

 fairly rich in lime. It makes cotton bear longer in the 



