8 SOILS AND FERTILIZERS 



nitrification, the nitrogen supply of crops, and on the 

 increase and decrease of the nitrogen of the soil when 

 different crops are produced, has had a most important 

 bearing upon maintaining the fertility of soils. 



" The general plan of the field experiments has been 

 to grow some of the most important crops of rotation, 

 each separately, for many years in succession on the 

 same land, without manure, with farmyard manure, 

 and with a great variety of chemical manures, the 

 same kind of manure being, as a rule, applied year after 

 year on the same plot. Experiments with different 

 manures on the mixed herbage of permanent grass 

 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, Bous- 

 singault, Liebig, and Lawes and Gilbert, a great 

 many others have contributed to our knowledge 

 of the chemistry of soils. The work of Pasteur, while 

 it did not directly relate to soils, indirectly had a great 

 influence upon soil investigations. His researches 

 upon fermentation made it possible for Schlosing to 

 prove that nitrification was the result of the workings 

 of living organisms which have since been isolated 

 and studied by YYarington and Winogradsky. 



Many of the more recent investigations relating to 

 the chemistry of soils are reviewed in the following 

 chapters. Our knowledge regarding the chemistry, 



