198 THE FARMER OF TO-MORROW 



"The researches of the several experiment 

 stations throughout the world and the inves- 

 tigations of our engineers on the amount of 

 material carried in solution and in suspen- 

 sion in our principal rivers and borne by the 

 wind establish the fact that loss through nat- 

 ural leaching and erosion removes far more 

 mineral plant food elements than do culti- 

 vated crops.* In cropping soils, therefore, 

 and removing the crop from the land, we re- 

 move an inconsiderable amount of mineral ma- 

 terial compared with normal losses to which 

 the soil is adjusted through natural laws. 



"The second point opposed to this book- 

 keeping system of accounting for the plant- 

 food constituents is that in a small majority 

 of analyses reported in this country and 

 abroad, where both soils and subsoils have been 

 examined, the upper soil, from which pre- 

 sumably the roots of annual plants take most 

 of their mineral matter, has a content of 

 potash and phosphoric acid higher than the 

 subsoil. 



"From the meager information to be found 

 in the works of the early agricultural writers 

 of Greece and Italy it seems probable that 

 the yields per acre obtained at the present 

 time are not much different from those ob- 

 tained in the earlier historic times. There are 



"The Mississippi River removes enough silt annually to cover 

 225,000 acres one foot deep. 



