OUTLINE AND TABLE OF CONTENTS XV 



PAGE 



(4) Improves the aeration (113). 



(5) Raises the average temperature (114). 



(6) Influences the growth of organisms (115). 



(7) Increases the food-supply (116). 



(8) Enlarges the root-zone (117). 



(9) Reduces "heaving" (118). 



(10) Removes injurious salts from alkali- soils 



(119). 



(11) Reduces erosion (120). 



(12) Increases crop-yields and improves sani- 



tary conditions (121). 



(b) Principles of drainage (122). 



(1) Open or surface drains (123). 



(2) Covered or under-drains (124). 



2. Other types of drainage (125). 



3. Surface culture (126). 



C. Plant Nutrients of the Soil 267 



I. Solubility of the soil through natural processes 267 



II. Solubility of the soil in various solvents 268 



a. Complete solution of the soil (127). 



b. Digestion with strong hydrochloric acid (128). 



1. Interpretation of results of analysis of hydro- 

 chloric acid solution (129). 



(a) Permanent fertility and manurial needs (130) 



(b) Relation of texture to solubility (131). 



(c) Nature of subsoil (132). 



(d) Calcium carbonate (133). 



(e) Estimation of deficiency of ingredients (134). 

 (J) Conclusions (135). 



c. Extraction with dilute organic acids (136). 



1. Advantages in showing manurial needs (137). 



2. Usefulness of citric acid (138). 



d. Extraction with aqueous solution of carbon dioxid 



(139). 



e. Extraction with pure water (140). 



1. Influence of absorption (141). 



2. Other factors (142). 



