152 SOIL CONDITIONS AND PLANT GROWTH 



organic matter was rapidly oxidised away, leaching and erosion in- 

 creased considerably when the cover of vegetation was removed, while 

 the compound particles that had slowly been forming through the ages 

 soon broke down. Nothing was returned to the soil, the grain and 

 other portable products were sold and the straw burnt. The result 

 has been a rate of exhaustion unparalleled in older countries, and 

 wholly beyond the farmer's power to remedy, consequently he left the 

 land and moved on. The excellent experimental studies of Hopkins 

 (139) at the Illinois Experimental Station, of Whitson (307) at Wis- 

 consin, and other American investigators, have shown that additions of 

 lime, of phosphates and sometimes of potassium salts, with the intro- 

 duction of rotations, including grass and leguminous crops, and proper 

 cultivations will slowly bring about a very marked improvement. 



