180 



Supposing this land was cropped annually, and the crop 

 removed from the ground 501bs. each of potash, phosphoric acitf, 

 and nitrogen, the ground would be completely exhausted of the 

 first in 600 years, of the second in 16 years, and of the third in 

 3,000 years. 



This assumption, however, wo aid be entirely unsupported in 

 practice. The high percentage of salt is an indication that the 

 land in question is badly drained ; in fact, it is often waterlogged, 

 and the soluble salts, instead of being washed out of the ground, 

 accumulate to an alarming .extent. The roots, then, of the more 

 tender crop plants instead of feeding on a layer of soil one foot deep, 

 would rot and corrode and only penetrate to a few inches. The 

 mass of plant food revealed by chemical analysis is in practice 

 found to be beyond the reach of the crops, and, besides, whatever 

 amount of that plant food lies within reach of the shallow roots of 

 the crop is of such a crude and raw quality that it is not in a fit 

 state to act as plant food. 



DIFFERENT SOURCES OF FERTILISERS. 



According to their origin or the sort of food stuff they supply 

 to plants, manures are spoken of as : 



"Animal Manures." These are characterised by the large 

 quantity of nitrogen they contain, and the ease with which they 

 decompose and yield their fertilising matter in available form e.g., 

 guanos, desiccated blood, bones, and superphosphate. 



" Vegetable Manures," which undergo decomposition more 

 slowly ; some, as the leguminous plants, having a large percentage 

 of nitrogen e.g., green manuring, farmyard manure, sea.-weeds, 

 and oil-cakes. 



" Mineral Manures," which are extracted from minerals, and 

 yield ash constituents to plants e.g., sulphate of ammonia, of lime, 

 of potash, nitrate of soda, of potash, lime, etc. 



Then again, manures are spoken of as " general " manures 

 when they contain all the necessary elements for plant growth, or 

 " special manures " when they only supply one or several of these 

 elements. 



These elements, again, are said to be " dormant," " latent," or 

 " active," according as they are insoluble or soluble in the corroding 

 liquid which exudes from the rootlets and are thus made available 

 for plant food or are locked up in an inert form in the soils. 



Fertilisers, however, for the practical purpose of the fruit- 

 grower and farmer, should be better considered as nitrogenous, 

 phosphatic, potassic, calcareous fertilisers, according as nitrogen, 

 phosphoric acid, or potash, or lime is the predominating valuable 

 constituent. 



Nitrogen is the rarest and most costly element of plant food ; it 

 occurs in abundance in the air as free nitrogen, but is not available 



