WHY SOILS BECOME EXHAUSTED. 149 



An inspection of the table above presented gives only a 

 faint idea of the extent to which the elements of fertility 

 are withdrawn from the soil in the regular course of crop- 

 ping. If we figure up the amount of mineral matters car- 

 ried off during the ordinary 4 course rotation of wheat, oats, 

 corn, and clover for 2 years, on a well cultivated farm, we 

 have the following results. 



Wheat. Oats. Corn. 2 years Clover. Total. 



Nitrogen 45. 52. 56. 204. 357. IbS. 



Sulphur 7.8 8.0 14.7 18.8 49.3 



Potash 27.9 * 38.1 58.0 174.8 298.8 



Soda 3.4 7.3 2.0 8.2 20.9 



Lime 10.2 11.8 15.7 172.2 209.9 



Magnesia 7.7 9.2 12.3 61.8 91.0 



Phosphoric acid.... 22.7 18.9 25.1 50.2 116.9 



Chlorine 1.9 5.5 18.8 26.2 



Silica .-111.1 94.1 54.5 13.6 273.3 



237~7 m9 238.3 722.4 1443.3 



The amount thus taken from the soil in 5 years is very 

 large, and considering that it is all derived from the stock 

 of soluble plant food existing in the soil, it is no matter for 

 surprise that 20 years of such cultivation should leave the 

 soil destitute of fertility and unable to bear the same abun- 

 dant crops. Indeed to such a condition of sterility have a 

 large portion of the cultivated lands in New England and 

 the Southern States been reduced by this process of exhaus- 

 tive culture that a larger expense will be required for their 

 restoration to even a moderate degree of fertility, than 

 would be equal to their value when thus restored. No far- 

 mer who lives by his mere labor, and who has not a large cap- 

 ital to spend in fertilizers and a slow costly process of re- 

 covery, can hope to do anything with these farms, many of 

 which are abandoned to the slow process of recovery by nat- 

 ural methods and the gradual accretion of carbon and 

 nitrogen from the sparse contributions of the atmosphere, 

 which may sustain a thin growth of weeds and humble 

 plants during a long series of years, the remains of which 

 may in time gather a sufficient provision for a new culture. 



It has been explained that some of the mineral constitu- 

 ents of a fertile soil exist in sufficient abundance for all the 

 requirements of cultivated crops for all time. Alumina and 



