No. 4.] NITROGEN AND FERTILITY. 169 



lirought results of great practical importance. When it is 

 considered that the whole commercial fertilizer industry, 

 involving thousands of pounds of plant food, worth millions 

 of dollars, rests upon this theory ; that the business is of 

 such importance that fertilizers are sold under close police 

 regulations, based upon chemical analyses, — one compre- 

 hends how sweeping these generalizations are, and how they 

 have entered into practical agriculture. 



This explanation is so simple and seemed so rational that 

 it is a thousand pities that it will not account for all of the 

 phenomena. It seems to serve better for everything else 

 than for nitrogen. Even Liebig saw that he could not sat- 

 isfactorily account for this element by known facts ; but he 

 and his successors confidently expected that new chemical 

 facts would be found that would explain and correlate the 

 peculiar facts observed about this element. 



Plant Food not All Available. 



Chemical analysis of the soils, however, showed that even 

 the meanest soil contained enough of nitrogen, Y)hosphoric 

 acid and potash to grow many crops. As ordinary soils 

 would not produce such crops, this plant food was supposed 

 to be unavailable, l)ut that in some way, by exposure to the 

 air, to water, etc., this unavailable plant food would by 

 chemical changes become available. That no known method 

 of soil analysis would indicate the fertility of soils was soon 

 learned ; and the so-called soil tests with fertilizers were in- 

 troduced, so as to overcome the limitations of the chemist's 

 knowledge, and put the "question directly to the soil it- 

 seh"." 



The inadequacy of the chemical method of the soil test is 

 shown by the fact that, while the top foot of a good soil 

 carries more than 3,500 pounds of nitrogen per acre, and a 

 crop of potatoes removes not more than 75 pounds of nitro- 

 gen in tubers and tops, it is frequently necessary to supply 

 more than that amount of nitrog-en in a fertilizer in order to 

 obtain a crop. It is much the same as though a man had 

 $3,500 on deposit in a bank, but before he could have his 

 draft for $75 honored he must make an additional deposit 

 of perhaps $150. 



