CHAPTER XXIII 



COMMERCIAL FERTILIZERS 



As treated in this volume, manures include all those 

 substances, with the exception of water (the function and 

 application of which is discussed in par. 167), that are 

 added to soils to make them more productive. There are 

 several ways in which manures applied to soils may in- 

 crease plant growth : (1) by addition of the nutrient mate- 

 rials utilized by plants, which is the chief function of 

 most of the so-called commercial fertilizers; (2) by im- 

 provement of the physical condition of a soil, which 

 usually results from the application of lime and the in- 

 corporation of organic matter ; (3) by favoring the action 

 of useful bacteria, which is one of the beneficial results 

 of farm manure and also of lime; (4) by counteracting 

 the effects of toxic substances — as, for instance, the 

 conversion of sodium carbonate into sulfate by gypsum, 

 or the neutralization of acidity, or possibly the destruc- 

 tion of toxic organic substances by certain salts ; (5) by 

 catalytic action, either on chemical processes in the soil 

 or by its influence on those bacteria that exert a favorable 

 influence on soil fertility or by direct stimulation of the 

 plant. 



410. Early ideas of the function of manures. — 

 Manures were at one time supposed to pulverize the soil, 

 and the French word manoeuvrer, from which the word 

 manure comes, implies to work with the hand. This 



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