CHAPTEE XVI. 



MANURIAL VALUE OF FEEDING STUFFS. 



413. Essential constituents of fertilizers. Only three of the 

 constituents which plants remove from the soil need be considered 

 in this chapter, viz., nitrogen, phosphoric acid and potash, for 

 all the others are usually held in such abundance that no thought 

 need be given them. While it is possible for the legumes to 

 gather nitrogen indirectly from the air, the supply from this source 

 is not always sufficient, and it is often necessary to add nitrogen 

 compounds to the soil for the purpose of enriching it. Phosphoric 

 acid and potash are the two mineral compounds which are not 

 always held by the soil in sufficient quantity to give profitable 

 crops and must be supplied in the form of manures or fertilizers. 



Farm-yard manures may benefit the soil because the vegetable 

 matter they contain acts as a mulch and forms humus, but so far 

 as feeding the plants is concerned their worth rests upon the nitro- 

 gen, phosphoric acid and potash they contain. 



414. Fertilizing constituents of feeding stuffs. The quantity of 

 nitrogen, phosphoric acid and potash found in the various feed- 

 ing stuffs is given in Table III of the Appendix. The examples 

 presented below are abstracted from that table for the purpose of 

 illustration: 



Table showing fertilizing constituents in 1,000 pounds of common 

 feeding stuffs From Table III of the Appendix. 



