In connection with the subject of fertilization the terms 

 manures, fertilizers, commercial fertilizers, chemical fertilizers, 

 indirect fertilizers, natural fertilizers, artificial fertilizers, super- 

 phosphate, complete and incomplete manures, etc., are used, and 

 as there is often a misunderstanding of the meaning of some of 

 these I will give a few definitions which may help us in the fol- 

 lowing pages. 



K fertilizer is any substance which furnishes deficient plant 

 food in an available form. 



Fertilizers are oithex natural or artificial ; the former includ- 

 ing manures, or the solid and liquid excrement of animals and 

 green crops plowed in to increase fertility. 



The latter, (artificial fertilizers) including commercial fertil- 

 izers, sometimes called prepared fertilizers, and chemical fertil- 

 izers, or those mixed from crude fertilizing chemicals. 



A fertilizer is complete, sometimes called general, when it 

 contains nitrogen, phosphoric acid and potash, and incomplete, 

 sometimes call special, when furnishing only one or two of these 

 deficient forms of plant food. Mixed animal manures are all 

 complete, or general, fertilizers. Green crops plowed under are 

 complete. The artificial fertilizers, whether commercial or 

 chemical, are complete or incomplete, according as they are 

 mixed from raw materials containing the three forms of plant 

 food above mentioned, or as they lack one or more of these. A 

 fertilizer is said to be indirect when it does not contain deficient 

 plant food, but in some way acts on the soil so as to hasten the 

 change of unavailable plant food in the soil into available, that 

 is, they increase the natural capacity of the soil. Lime, gypsum, 

 salt, etc., so far as they have any action, belong to this class ; 

 others, like ashes, and especially leached ashes, are both direct 

 (furnishing plant food) and indirect. 



SOURCES OF PLANT FOOD. 



We are now in position to inquire about the sources of plant 

 food, and for our present purposes only the deficient plant food 

 will receive attention, that is, nitrogen, phosphoric acid and 

 potash. 



Farm yard manure is the chief source of plant food in mix- 

 ed agriculture. It consists of two parts, solid and liquid, the 

 solid portion represents that part of the food which is not di- 



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