Plant Food in the Soil 



We will now examine the sources of various plant foods, 

 and will first deal with nitrogen. 



We have explained that nitrogen exists as 



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from which our crops must derive it, it must 



be in some combination, and that the final form in which 

 plants use it is in combination of nitric acid with a base, 

 forming a nitrate of Hme, potash, or some other base in 

 the soil. When it is reduced to this available form it is 

 so readily soluble that it washes out of the soil more rap- 

 idly than any other form of plant food, and hence must be 

 more frequently renewed in the soil. Then, too, when 

 the vegetable matter in the soil is rapidly oxidized or burnt 

 up by the continuous cultivation of one crop year after 

 year on the same land, as our cotton farmers and the 

 wheat farmers of the Northwest have been doing, there is 

 a serious loss into the air more than through the cropping. 

 Nitrogen, when purchased in any form, is always the most 

 costly of all the plant foods that make up our commercial 

 fertihzers. It is found in all decay of vegetable or animal 

 matter, and is then known as organic nitrogen. A soil 

 abounding in humus or vegetable decay is usually supplied 

 with nitrogen more or less available. One special value 

 of stable manure is in the organic matter which is applied 

 with it, and which, having to pass through the process of 

 nitrification in the soil through the agency of bacteria, 

 makes the more lasting effect of such treatment. We also 

 get nitrogen in an organic form more readily available in 

 the dried blood from the great slaughterhouses. When 

 this is carefully dried and is of a red color it is far more 

 valuable than that which has heated and has turned to a 



