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receive the following proportions of phosphoric acid, 

 potash, lime, magnesia, and silicic acid : 



Phosphoric p-*...!, Lime and Silicic 

 Acid. Potash. Magneala Acld> 



Wheat (corn and straw) ...... 1 2'0 0'7 6-7 



Potatoes (tubes) ............... 1 3'2 0'48 0'4 



Oats (corn and straw) ......... 1 21 1'03 6'0 



Clover .............................. 1 2-6 4-0 1-0 



Average ........ . _ l_ fc 2-5 T5 3'0 



" Supposing wheat, potatoes, oats, and clover to be culti- 

 vated in a field for four years in succession, each of these 

 plants will absorb from the soil the proportion of mineral 

 constituents which it requires ; and the sum total, divided 

 by the number of years, viz., four, shows the average 

 relative proportion of all the nutritive substances which 

 the soil has lost. 



Phosphoric p ftfaa >, Lime and Silicic 

 Acid. rotash. Magnesia> Aci(lt 



If in the formula ...... n(l'0 2'5 1-5 3-0) 



we determine the value of w, which is meant here to 

 designate the number of kilogrammes of phosphoric acid 

 which the four crops have received from the soil, we find 

 for the wheat crop 26 kilogrammes of phosphoric acid, 

 for the potato crop 25 kilogrammes, for the oat crop 27 

 kilogrammes, and for the clover crop 36 kilogrammes. 

 Altogether 114 kilogrammes; multiplying the above 

 proportional numbers by this number, we obtain the sum 

 total of all the nutritive substances extracted from the 

 soil by the four crops. With the help of these propor- 

 tional numbers, we are better able than before to give 

 some more accurate explanations. 



" Suppose that the soil of a certain field contains, in 

 an available state, the requisite quantities of phosphoric 

 acid, potash, lime, and magnesia to supply the four 



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