III.] 



WATER RETAINED BY THE SOIL 



75 



culty in escaping, so that even after long-continued 

 rain the pore space does not become entirely rilled 

 with water. 



The following table shows the water contained 

 in a few field soils sampled a day or two after the 

 cessation of long-continued rain, and calculated as 

 percentages of the wet soil by weight : 



Sand at Water Level . 

 Rothamsted Wheat Land, 



Light Loam above Chalk 



unmanured .... 

 manured with artificials 

 manured with dung for 26 years 



Per cent, of 



Water 

 in Wet Soil. 



18.4 

 23-0 

 247 

 37-6 

 20-3 



Hellriegel has shown that the optimum proportion 

 of water in the soil for the growth' of the plant is 

 40 to 50 per cent, of the maximum required for satura- 

 tion. 



Flozv of Water through Soils. 



The freedom with which water will move through 

 soils under the action of gravity or other force will 

 depend not only on the pore space, but upon the 



