CHAPTER IV. 



NITROGEN. DECOMPOSITION OF NITROGENOUS 

 COMPOUNDS. 







The nitrogenous foods of plants are next in importance to carbon 

 dioxid and water. Plants cannot grow without nitrogen, and they 

 need it in larger quantity than any other mineral foods. The ni- 

 trogenous fertilizers have commonly a more noticeable effect in 

 stimulating crops than other minerals. The amount of material 

 in the world that can serve directly as nitrogen food for plants is 

 decidedly limited, and therefore it is expensive. For these as well 

 as other reasons, the problem of continued soil fertility is more 

 closely bound up with the matter of nitrogen than any other chemical 

 element. 



SOURCES OF NIROGENOUS FOOD. 



Plants take their nitrogen from the soil, chiefly in the form 

 of nitrates. While it is true that they can utilize ammonium 

 salts also, under ordinary conditions ammonia furnishes little 

 food directly to the plant, the far larger part being furnished 

 by soil nitrates. The amount of nitrate in any soil is however, 

 very limited, there being only from o.i per cent, to 0.2 per cent, 

 in ordinary soils. As crop after crop is grown, the small amount in 

 the soil is gradually used up and must be replaced if the soil is to 

 continue yielding crops. The farmer buys nitrates in the form of 

 commercial fertilizers to replace the amount taken from his soils by 

 his crops. These commercial nitrates, however, are also limited 

 in amount. They are confined to a few deposits of nitrates, chiefly 

 in warm dry regions. The best known come from Chili, whose 

 nitrate mines to-day furnish the greater part of the nitrates for the 



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