CHAPTER VIII 



THE POWER OF THE SOIL TO ABSORB SALTS 



Retention of Manures by the Soil — The Absorption of Ammonia 

 and its Salts ; of Potash ; of Phosphoric Acid — Chemical and 

 Physical Agencies at Work — The Non-Retention of Nitrates 

 — The Composition of Drainage Waters — Loss of Nitrates 

 by the Land — Time of Application of Manures. 



Many of the substances employed as manures are 

 soluble in water, hence it becomes important to ascer- 

 tain what is likely to be their fate in the soil, when 

 their application is followed by sufficient rain to cause 

 percolation into the subsoil. Of substances contain- 

 ing nitrogen, nitrate of soda, the salts of ammonia, 

 urea, and kindred bodies, are freely soluble in water; 

 superphosphate alone of the compounds of phos- 

 phoric acid commonly used as manure is soluble; but 

 sulphate, chloride, and carbonate of potash are easily 

 soluble. 



Not long after the principles underlying the nutri- 

 tion of plants had been established, Thompson and Way 

 showed that ordinary soil possesses the power of with- 

 drawing most of the above substances from solution, 

 and so saving them from washing away into the subsoil 

 or the drains. Some of the salts, like sulphate of 

 ammonia, are decomposed, the base alone being re- 



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