CHAPTER VI 



CULTIVATION AND THE MOVEMENTS OF SOIL WATER 



Nature of the Film of Liquid surrounding Wet Particles of Soil. 

 Retention and Movements of Water due to Surface Tension. 

 Percolation. Rise of Subsoil Water by Capillarity. Value of 

 Autumn Ploughing. Effect of Spring Cultivations. Cooling 

 of the Land by Evaporation. Effect, of Hoeing and Rolling 

 upon the Temperature and Water-content of the Soil. Dry 

 Farming in Semi-arid Regions. Drainage and the Tempera- 

 ture of Soils. Spring Frosts. Early and Late Soils. 



Somewhat earlier in the book an experiment was 

 described (p. 91) which had for its object the deter- 

 mination of the relative powers of different soils to 

 retain water, though the water was given every 

 opportunity of draining away. It will now be necessary 

 to ask how the soils effect this retention of water, 

 because on this depend many of the properties of soils 

 which are important to the farmer. It is not easy to 

 observe what is going on in the soil itself, because the 

 particles are so small, but we can obtain a convenient 

 illustration by means of a model on a large scale. 

 Procure a dozen or so large beads and thread them on 

 three or four strings from a stick, so as to form a little 

 rectangle of beads hanging vertically and all in contact ; 

 this may be taken to represent an imaginary section of 

 the soil greatly magnified. Now dip the beads in oil 

 and lift them out to drain, or better still, dip them in 



melted wax for a few moments, so that after lifting them 

 100 



