340 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



4 per cent, nitrogen, and 10 per cent, potash, costing $25.00 per 

 ton. The average of the four crops is as follows : 



The first 500 pounds fertilizer produced an increase of 23.3 

 bushels potatoes, a cost of 27 cents per bushel for fertilizer. The 

 last 500 pounds produced 6.0 bushels at a cost of $1.04 per bushel 

 for. the fertilizer. 



Secondary Actions of Fertilizers. The supplying of available 

 plant food is the primary action of fertilizers. They have other 

 secondary actions upon the soil, which may not be unimportant at 

 times. 



Reaction. Sulphate of ammonia leaves an acid residue in the 

 soil, which unites with lime, increases the loss of lime, and may 

 cause a soil not rich in lime to become acid. This has taken 

 place at the Woburn (England) Experiment- Farm, where the 

 plot which receives sulphate of ammonia has become acid and will 

 not grow barley. Addition of lime corrects the acidity. 



Acid phosphate may also have a slight tendency towards caus- 

 ing soil acidity. Nitrate of soda leaves a basic residue in the soil, 

 and hence has a tendency to correct acidity. Organic nitrogenous 

 fertilizers do not affect the reaction of the soil. 



Physical Structure. Acid phosphate tends to flocculate a clay 

 soil. Nitrate of soda tends to cause it to puddle or run together. 

 Potash salts vary somewhat in their action, according to the 

 nature of the soil. 



Fertilisers Conserve Moisture. Fertilizers may decrease trans- 

 piration and reduce the quantity of water required to produce 

 growth. For example, Widstoe reports the quantity of water 



