CONTENTS 



PAGES 



INTRODUCTION i-io 



Early uses of manures and explanation of their action 

 by alchemists ; Investigations prior to 1800 : Work of De 

 Saussure, Davy, Thaer, and Boussingault ; Liebig's writ- 

 ings and their influence ; Investigations of Lawes and Gil- 

 bert ; Work of Tull ; Contributions of other investigators ; 

 Agronomy; Value of soil studies. 



CHAPTER I 



PHYSICAL PROPERTIES OF SOILS n-53 



Chemical and physical properties of soils considered ; 

 Weight of soils ; Pore space ; Specific gravity ; Size of soil 

 particles ; Clay ; Sand ; Silt ; Form of soil particles ; Num- 

 ber and arrangement of soil particles ; Mechanical analysis 

 of soils ; Crop growth and physical properties. Soil types : 

 Potato and truck soils ; Fruit soils ; Corn soils ; Me- 

 dium grass and grain soils ; Wheat soils ; Sandy, clay, 

 and loam soils. Relation of the soil to water ; Amount of 

 water required for crops ; Bottom water ; Capillary water ; 

 Hydroscopic water ; Loss of water by percolation, evapo- 

 ration, and transpiration ; Drainage ; Influence of forest 

 regions ; Influence of cultivation upon the water supply 

 of crops ; Capillary water and cultivation ; Shallow surface 

 cultivation ; Cultivation after rains ; Rolling ; Subsoiling ; 

 Fall plowing ; Spring plowing ; Mulching ; Depth of 

 plowing ; Permeability of soils ; Fertilizers and their in- 



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