Xll 



TABLE OF CONTENTS 



Sources of soil heat, 209 Factors affecting soil tem- 

 perature, 210 Specific heat, 211 Variations of spe- 

 cific heat, 212 Specific heat based on volume of soil, 

 213 Effect of water on specific heat, 214 Absorptive 

 power of soils for heat, 215 Effect of color on absorp- 

 tion of heat, 216 Effects of texture and structure on 

 heat absorption, 217 Radiation of heat by soil, 218 

 Conductivity and convection of heat in soils, 219 

 Measurement of conductivity, 220 Effect of texture 

 on conductivity of heat, 221 Effects of humus and 

 structure on conductivity, 222 Influence of moisture 

 on heat conductivity in soil, 223 Effect of evaporation 

 of water on soil temperature, 224 Effect of organic 

 decay on soil temperature, 225 Relation of slope to 

 soil temperature, 226 Heat supply and its effects, 227 

 Control of soil temperature, 228. 



CHAPTER XV 



AVAILABILITY OF PLANT NUTRIENTS AS DETERMINED BY 

 CHEMICAL ANALYSIS ...... 



Solubility of the soil in various solvents, 229 Com- 

 plete solution of the soil, 230 Partial solution with 

 strong acids, 231 Significance of a strong hydrochloric 

 acid analysis, 232 Relation of texture to solubility, 

 233 Nature of the subsoil, 234 Calcium carbonate, 

 235 Deficiency of ingredients and manurial needs, 236 

 Partial solution with weak acids, 237 Advantages 

 in the use of dilute acids, 238 The one-per-cent citric 

 acid method, 239 Usefulness of the citric acid method, 

 240 Dilute mineral acids, 241 Extraction with an 

 aqueous solution of carbon dioxide, 242 Extraction 

 with pure water, 243 Influence of absorption, 244 

 Other factors influencing extraction, 245 The soil solu- 

 tion in situ, 246 Devices for obtaining a soil solution, 

 247 Composition and concentration of the soil solu- 

 tion, 248 Variability in composition and concentration 

 of the soil solution, 249 Discussion of the theories 

 regarding soil solutions, 250. 



327-348 



