x CONTENTS. 



Ground Water most Favorable to Crops, 228. Moisture Supplied by Tap 

 Roots, 229. Reserve of Capillary Water, 229. Injurious Rise of Bottom 

 Water from Irrigation, 230. Consequences of the Swamping of Irrigated 

 Lands ; Prevention, 231. Permanent Injury to certain Lands, 231. 

 Reduction of Sulfates, 232. Ferruginous or Red Lands, 233. 



CHAPTER XIII. 



WATER OF SOILS ; THE REGULATION AND CONSERVATION OF SOIL MOIST- 

 URE ; IRRIGATION, 234. Loosening of the Surface, 234. Effects of 

 Underdrains ; Rain on Clay Soils, 235. Winter Irrigation, 236. 

 Methods of Irrigation, 236. Surface Sprinkling, 237. Flooding, 237. 

 Check Flooding. Furrow Irrigation, 237, 238. Figure Showing Pen- 

 etration, 239. Figure Showing Faulty Irrigation in Sandy Lands, 239. 

 Distance between Furrows and Ditches, 241. Irrigation by Lateral 

 Seepage, 242. Basin Irrigation of Trees and Vines ; Advantages and 

 Objections, 243. Irrigation from Underground Pipes, 245. Quality of 

 Irrigation Wafers, 246. Saline Waters ; Figures of Effects on Orange 

 Trees, 246. Limits of Salinity, 246. Mode of Using Saline Irrigation 

 Waters ; Apparent Paradox, 249. Use of Drainage Waters for Irrig- 

 ation, 250. " Black Alkali " Waters, 250. Variations in the Salinity 

 of Deep and Shallow Wells, 250. Muddy Waters, 251. The Duty oj 

 Irrigation Waters, 251. Causes of Losses, 252. Loss by Percolation. 

 Figure, 252. Evaporation, 253. Tables Showing same at California 

 Stations, 255. Evaporation in Different Climates ; Table, 255. Evapo- 

 ration from Reservoirs and Ditches, 257. Prevention of Evaporation ; 

 Protective Surface Layer, 257. Illustrations of Effects of Tillage ; 

 Table, 258. Evaporation through Roots and Leaves, 262. Weeds 

 waste Moisture, 264. Distribution of Moisture in Soils as Affected by 

 Vegetation, 264. Forests and Steppes, 265. Eucalyptus for Drying 

 Wet Lands, 265. Mulching; Effects on Temperature and Moisture, 266. 



CHAPTER XIV. 



ABSORPTION BY SOILS OF SOLIDS FROM SOLUTIONS. ABSORPTION OF GASES, 

 AIR OF SOILS, 267. Absorption of Solids, 267. Desalation, 267. Deco- 

 lorization, 267. Complexity of Soil-Action, Physical and Chemical, 

 268. " Purifying" Action of Soils on Gases and Liquids, 269. Waste 

 of Fertilizers, 269. Variation of Absorptive Power, 270. Generalities 

 Regarding Chemical Action and Exchange, 270. Drain Waters, 271. 

 Distinctions not Absolute, 272. Absorption or Condensation of Gases 

 by the Soil, 272. Proof of Presence of Carbonic and Ammonia Gases in 

 Soils, 273. Absorption of Gases by Dry Soils. Figure, 274. Composi- 

 tion of Gases Absorbed by Various Bodies from the Air. Table, 275. 

 Discussion of Table, 277. The Air of Soils, 279. Empty Space in 

 Dry Soils, 279. Functions of Air in Soils, 279. Insufficient and Ex- 

 cessive Aeration, 280. Composition of the Free Air of Soils, 280. Car- 

 bonic Dioxid vs. Oxygen, 281. Relation to Bacterial and Fungous 

 Activity, 281. Putrefactive Processes, 282. 



