IX.] BAD TILTH DUE TO FERTILISERS 253 



experiments with water cultures, it can also be extracted 

 from the soil of the Rothamsted plots which have for 

 many years been manured with nitrate of soda. Small 

 as the amount may seem to be, it is quite sufficient to 

 account for the deflocculation of the clay and the 

 defective tilth observed on heavy land after nitrate of 

 soda has been used. 



The bad repute of nitrate of soda as exhausting or 

 scourging the land, is less due to any sensible diminution 

 in the stock of plant food in the soil that follows its use, 

 than to the deflocculation it sometimes induces, and the 

 consequent deterioration of the texture of the soil. 

 As a remedy lime is not effective, since it is an alkali 

 itself; instead the nitrate of soda should be used in 

 conjunction with acid flocculating manures like super- 

 phosphate, or a mixture of nitrate of soda and sulphate 

 of ammonia should be used as a nitrogenous manure, 

 because the two manures will act upon the soil in 

 opposite ways, the nitrate of soda as an alkali and the 

 sulphate of ammonia as an acid. Dressings of soot are 

 also effective; not only does it assist the soil mechanically, 

 but also the small percentage of sulphate of ammonia it 

 contains possesses some power of flocculating the clay. 



Other fertilisers which give rise to an alkaline 

 reaction in the soil are sulphate of potash, common 

 salt, and other soluble salts of sodium and potassium, 

 which as has already been noticed (p. 217) interact 

 with calcium carbonate in the soil, and give rise to a 

 little soluble alkaline carbonate. The injurious effects 

 of sulphate of potash upon the tilth of the heavy soil 

 at Rothamsted is very evident on the mangold field, 

 where the plots receiving this fertiliser every year 

 become excessively sticky and clinging in wet weather, 

 and dry, with a hard caked surface. It has often been 

 noticed that applications of potash salts and common 



