THE I SOIL IN RELATION TO PLANT GROWTH 131 



stand for, remain untouched. A distinction is therefore made between 

 the temporary fertility or " condition " within the cultivator's control, 

 and the " inherent " fertility that depends on the unalterable ultimate 

 particles. Of course the distinction is very indefinite and, in practice, 

 wholly empirical, no proper methods of estimation having yet been 

 worked out, but it is of importance in compensation and valuation 

 cases. 



Serious soil exhaustion did not arise under the old agricultural 

 conditions where the people practically lived on the land and no 

 great amount of material had to be sold away from the farm. Phos- 

 phate exhaustion was the most serious occurrence, and as the original 

 supplies were not as a rule very great, it must have become acute by 

 the end of the eighteenth century in England, for remarkable improve- 

 ments were, and still are, effected all over the country by adding phos- 

 phates. Then began a process, which has gone on to an increasing 

 extent ever since, of ransacking the whole world for phosphates ; at 

 first the search was for bones, even the old battlefields not being 

 spared if we may believe some of the accounts that have come down ; 

 later on (in 1 842) Henslow discovered large deposits of mineral phos- 

 phates to which more and more attention has been paid. 



The crowding of the population into cities, and the enormous 

 cheapening of transport rates, led during the nineteenth century to the 

 adoption in new countries, particularly in North America, of what is 

 perhaps the most wasteful method of farming known : continuous arable 

 cultivation without periodical spells of leguminous and grass crops. The 

 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. 



