8 SOILS AND FERTILIZERS 



land, on the effects of fallow, and on the actual course 

 of rotation without manure, and with different manures 

 have likewise been made." 4 



In addition to Davy, Thaer, DeSaussure, Boussin- 

 gault, Liebig, and Lawes and Gilbert, a great many 

 others have contributed to our knowledge of the prop- 

 erties of soils. The work of Pasteur, while it did not 

 directly relate to soils, indirectly had great influence 

 upon soil investigations. His researches upon fermen- 

 tation made it possible for Schlosing to prove that 

 nitrification is the result of the workings of living 

 organisms. These have since been isolated and studied 

 by Warington and Winogradsky. 



The importance of the physical condition of the soil 

 and its relation to crop production was recognized by 

 agriculturists at about the same time that the sources 

 of plant food were being investigated. Jethro Tull 

 published in 1829 a work entitled "The Horse-Hoeing 

 Husbandry," which emphasized the importance of 

 thorough cultivation of the soil. That increase in the 

 yield of crops, destruction of weeds, reduction of rust 

 and blight of wheat, and general improvement of the 

 soil, are all results of improved tillage is clearly set 

 forth in Tull's work. Tull was inclined to believe that 

 tillage could take the place of manure. " All sorts of 

 dung and compost contain some matter which, when 

 mixed with the soil, ferments therein ; and by such fer- 

 ment dissolves, crumbles, and divides the earth very 

 much. This is the chief and almost only use of dung." 



