148 MANURES. VII. 



Soils deficient in lime compounds can be more suitably 

 manured with nitrate of soda. 



2. Nitrate of soda is easily washed out of the soil by rain and 



in wet seasons a considerable amount of it is lost. It 

 should only be applied when the plant can assimilate it. 

 Sulphate of ammonia, though equally soluble in water, 

 is not washed out by rain to any appreciable extent, but 

 is held by the humus and perhaps by the hydrated 

 silicates and the ferric hydroxide until nitrification 

 occurs. Sulphate of ammonia is therefore preferable in 

 wet seasons and gives the best results- when applied at 

 the time of sowing, or even before. Nitrification can 

 only take place in the presence of sufficient, and is 

 favoured by increased, moisture, short of complete 

 saturation, so that in dry seasons sulphate of ammonia 

 is not so suitable as nitrate of soda. 



3. On soils very rich in calcium carbonate, ammonium sul- 



phate, if used as top-dressing, may suffer decomposition, 

 with loss by volatilisation of ammonium carbonate, 

 especially in dry weather. This loss can be prevented 

 by ploughing or harrowing the sulphate into the soil 

 immediately after its application. 



4. Both nitrate of soda and sulphate of ammonia will only 



yield the best results when the soil is abundantly sup- 

 plied with the necessary mineral constituents of plant 

 food. 



5. Nitrate of soda, not being absorbed by any of the con- 



stituents of the soil, penetrates into the subsoil and 

 thus favours the production of deep roots, which gives 

 the plant a better chance of finding mineral food and 

 of withstanding drought. 



6. Nitrate of soda is best applied in several small dressings, 



while sulphate of ammonia may generally be applied in 

 one. The usual quantities are from 1 to l-|cwt. of the 

 former and 100 to 150R). of the latter per acre, but with 

 certain crops, e.g., mangolds and potatoes, larger quan- 

 tities may be used. 



Potassium Nitrate. This substance, though doubly valu- 



