EXPERIMENTS ON CLOVER-SOILS. 151 



" In separate portions of the three layers of soil, the proportions 

 of nitrogen and phosphoric acid contained in each layer of six 

 inches, were determined and found to be as follows : 



Soil dried at 212 deg. Fahr. 

 lat MX KJ, mx 3d nix 

 inches, inches, inches. 



Percentage of phosphoric acid 249 .1^4 .172 



Nitrogen 1.62 .092 .064 



Equal to ammonia 198 . 112 .078 



" In the upper six inches, as will be seen, the percentage of both 

 phosphoric acid and nitrogen, was larger than in the two follow- 

 ing layers, while the proportion of nitrogen in the six inches of sur- 

 face soil, was much larger than in the next six inches ; and in the 

 third section, containing no visible particles of root-fibres, only 

 very little nitrogen occurred. 



" In their natural state, the three layers of soil contained : 



1st six 2d kix 3d six 

 indies, inches, inches. 



Moisture 17.16 18.24 16.62 



Phosphoric acid 198 .109 .143 



Nitrogen 131 .075 .053 



Equal to ammonia 1CU .091 .064 



Ibs. Z&. ibs. 

 Weight of one foot square of soil GO 61 63 



" Calculated per acre, the absolute weight of one acre of this 

 land, six inches deep, weighs : 



Lbs. 



1st six inches 2,613,600 



2d six inches 2,657,160 



3d six inches 2,746,280 



" No great error, therefore, will be made, if we assume in the 

 subsequent calculations, that six inches of this soil weighs two and 

 one-half millions of pounds per acre. 



" An acre of land, according to the preceding determinations, 

 contains : 



1st six inches, 2d six incJws, 3d six inches, 

 Lbs. Lb\ Lbs. 



Phosphoric acid 4,950 2,725 3,575 



Nitrogen 3,350 1,875 1,325 



Equal to ammonia _i- 050 g ' 275 



" The proportion of phosphoric acid in six inches of surface soil, 

 it will be seen, amounted to about two-tenths per cent ; a propor- 

 tion of the whole soil, so small that it may appear insufficient 

 for the production of a good corn-crop. However, when calcu- 

 lated to the acre, we find that six inches of surface soil in an acre of 

 land, actually contain over two tons of phosphoric acid. An aver- 

 age crop of wheat, assumed to be 25"bushels of grain, at 60 Ibs. per 



