CONTENTS 



INTRODUCTION 



Early uses of manures and explanation of their action by alche- 

 mists ; Investigations prior to 1800 : Work of De Saussure, Davy, 

 Thaer, and Boussingault ; Liebig's writings and their influence ; 

 Investigations of Lawes and Gilbert ; Contributions of other in- 

 vestigators ; Agronomy ; Value of soil studies. Pages i-S. 



CHAPTER I 



Physical Properties of Soils. Chemical and physical properties 

 of soils considered ; Weight of soils ; Size of soil particles ; Clay ; 

 Sand ; Silt ; Form of soil particles ; Number and arrangement of 

 soil particles ; Mechanical analysis of soils ; Crop growth and phys- 

 ical properties. Soil types Potato and truck soils ; Fruit soils ; 

 Corn soils ; Medium 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 ; Hydro- 

 scopic water ; Loss of water by percolation, evaporation and trans- 

 piration ; Drainage influence of forest regions ; Influence of culti- 

 vation upon the water supply of crops ; Capillary water and culti- 

 vation ; Shallow surface cultivation ; Cultivation after rains ; Roll- 

 ing ; Sub-soiling ; Fall plowing; Spring plowing ; Mulching; Depth 

 of plowing ; Permeability of soils ; Fertilizers and their Influence 

 upon moisture content of soils ; Farm manures and soil moisture ; 

 Relation of soils to heat ; Heat from chemical reactions within the 

 soil ; Heat and crop growth ; Organic matter and iron compounds ; 

 Color of soils ; Odor and taste of soils ; Power to absorb gases ; 

 Relation of soils to electricity ; Importance of physical properties 

 of the soil. Pages 9-44. 



CHAPTER II 



Geological Formation and Classification of Soils. Agricultural 

 geology ; Formation of soils ; Action of heat and cold ; Action of 

 water ; Glacial action ; Chemical action of water ; Action of air and 

 gases ; Action of micro-organism ; Action of vegetation ; Combined 

 action of the various agents ; Distribution of soils ; Sedentary and 



