THE SOIL IN RELATION TO PLANT GROWTH 321 



away from the farm. Phosphate exhaustion was the most 

 serious occurrence because there was no way of meeting it, 

 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 improvements were, and still are, 

 effected all over the country by adding phosphates. 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 battle-fields not 

 being spared, if we may believe some of the accounts that 

 have come down; later on (in 1842) Henslow discovered 

 large deposits of mineral phosphates, to which more and more 

 attention has been paid. Phosphate supplies may yet become 

 the factor that will determine the course of history. 



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, particu- 

 larly 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 increased 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 Hop- 

 kins (138) at the Illinois Experimental Station, of Whitson 

 (307) at Wisconsin, and other American investigators, have 

 shown that additions of lime, of phosphates, and sometimes of 

 potassium salts, with the introduction of rotations including 

 grass and leguminous crops, and proper cultivations will 

 slowly bring about a very marked improvement. 



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