Agricultural Chemistrij. 



285 



cannot be explained by supposing' the natural sources of nitrog^en 

 to be incapable of supplying to these plants enough of nitrogen for 

 a full crop, because the cultivation of green crops proves that 

 these natural sources can supply from twice to four times as 

 much nitrogen as is required for a full crop of wheat. We must 

 seek elsewhere, in other relations, for the true reason of this 

 necessity. 



The views on this subject, to which I was led in 1843, were 

 not a little fortified when, in 1846, by means of the analyses of 

 twenty-two soils which I caused to be made in my laboratory in 

 Giessen by Dr. Kroker, now Professor in Breslau, I acquired the 

 conviction that one acre of the most unfruitful soil, taken to the 

 depth of only 10 inches, contains more than a hundred times, and 

 one acre of fertile soil as much as from five hundred to a thousand 

 times, more nitrogen than is required for the heaviest crop of 

 wheat, or than is given to it in the most liberal supply of manure. 

 (See my ' Agricultural Chemistry,' 4th edition, p. 275.) 



The fact of the presence of this enormous amount of nitrogen 

 in the soil has been confirmed by the researches made at the 

 instance of the Royal College of Rural Economy in Berlin (' An- 

 nalen der Landwirthschaft,' vol. xiv. p. 2). The College of 

 Rural Economy caused land of apparently uniform quality to be 

 selected in fourteen different localities in Prussia for these experi- 

 ments. At ten or twelve different points of each of these fields 

 an equal quantity of earth was taken by the spade from the entire 

 depth of the arable soil ; these portions, in each case, were 

 thoroughly mixed, and from the mass samples were taken. 



In each sample the amount of nitrogen was determined by 

 three different chemists sejmratelg^ and from their results have been 

 calculated for one acre of land, to tlie depth of one foot (the 

 specific gravity of the soil being taken at 1"5), the following 

 quantities of nitrog^en, expressed however in pounds of ammonia 

 (17 lbs. of ammonia contain 14 lbs. of nitrogen) : — 



No. 

 1. 



4. 



5. 



6. 



7. 



8. 



5). 

 10. 

 11. 

 12. 

 13. 

 14. 



Soil 



I^icality. IJjs. of Ammonia. 



om HavixLoc 18,040 



lUirj^wesi'lebcu .. .. 17,220 



Tur<^ait.schoii .. .. 14, .'^50 



Walhip 13,120 



Ikesdau 7,790 



Turwo 7,3S0 



DalluMm (),970 



Jjaasoin 5,740 



Eldc'iKv 5,330 



]Uir;ibonih(.ini .. .. 5,330 



Ni'ucnnmii<l .. .. 4,510 



I'VankciiR'ld .. .. 4,100 



Nt'uhof 4,ii20 



Cart Ion 2,870 



