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CHAPTEE VII. 

 MANURES. Continued. 



IN the previous chapter the chief organic manures have 

 been described ; it remains to consider the other substances, 

 generally of mineral or artificial origin, which are employed 

 as fertilisers. They may be conveniently divided into four 

 groups : 



I. Nitrogenous manures. 

 II. Phosphatic manures. 



III. Potash manures. 



IV. Miscellaneous. 



Many of the organic manures already described contain 

 variable quantities of all the chief manurial substances, but 

 those about to be dealt with are, as a rule, intended to supply 

 only one important item of plant food. Their employment 

 gives the farmer, therefore, the pow r er of applying exactly what 

 he thinks may be necessary, without the introduction of other 

 plant food with which his land may already be abundantly 

 provided. Their general introduction into farming practice 

 has thus rendered easy a far more scientific treatment of the 

 soil than was possible with complex manures only. 



I. NITROGENOUS MANURES. These include the two 

 important substances sodium nitrate and ammonium sulphate, 

 also the less abundant and more expensive potassium nitrate. 



Sodium Nitrate, " Chili Saltpetre," occurs in the enormous 

 nitrate deposits of Peru, Chili, and Bolivia. It is found in 

 rainless districts and comparatively near the surface, covering 

 a huge desert devoid of both animal and vegetable life. The 

 raw product, known as caliche, is found beneath a covering 

 consisting of two layers, the upper one of sand and gypsum 

 and the lower of baked clay and gravel ; beneath the caliche is 

 a soft earth known as cova. The thickness of the caliclie varies 



