xiv TABLE OF CONTENTS 



CHAPTER IV 



PAGES 



SAVING WATER BY CULTIVATION 40-63 



The run-off, 40 The upward movement of water, 42 

 Intensity of evaporation, 44 Conditions determining 

 evaporation, 46 Mulching to check evaporation, 49 

 Self-mulching soils, 52 Time of cultivation, 53 

 Depth of cultivation, 55 Frequency of cultivation, 58 

 Cultivation and soil fertility, 59 Rolling, 62. 



CHAPTER V 



SOIL CHANGES DUE TO IRRIGATION WATER .... 64-107 



Contraction and moisture film, 64 Cohesion of soil 

 particles, 65 Volume changes of soils, 67 Effect on top 

 soil, 69 Successive wetting and drying, 70 Natural 

 packing of soil, 70 Soil temperature, 71 Water a 

 universal solvent, 72 Humid and arid soils contrasted, 

 73 Continuous solubility of soils, 74 Absorption by 

 soils, 76 Composition of drainage water, 78 Concen- 

 tration of soil moisture, 79 Loss by drainage, 79 

 Upward leaching, 81 Salinity of river waters, 82 

 Salinity of lake waters, 86 Salinity of mineral springs, 

 86 Soil moisture and natural waters compared, 87 

 Ash constitutents added by irrigation water, 87 Use of 

 concentrated waters, 89 Need of water surveys, 90 

 Composition of natural waters, 90 Classification of 

 natural waters, 92 Plant-food value of irrigation 

 water, 93 Suspended matter in river water, 95 Sea- 

 sonal variation of suspended matter, 98 Suspended 

 matter added to soil by irrigation, 100 Suspended 

 matter derived from surface soils, 100 Composition of 

 river sediments, 101 Physical effects of sediments, 

 102 Cultural treatment of sediments, 103 Effect of 

 sediments on crop-yields, 104 Water and soil life, 

 104. 



