1 1 8 T1LLA GEMO VEMENTS OF SOIL WA TER [chap. 



arable field the ground below will generally be found 

 cool and damp. The vineyards of the Rhine, etc., are 

 generally set on steep slopes very thoroughly drained 

 and exposed to the sun ; it will be noticed that the 

 utmost care is taken to keep the surface of the soil 

 covered with the broken slaty rock. 



Effect of Rolling. 



Though it has been pointed out that maintaining a 

 loose tilth on the surface is the most effective means 

 possessed by the farmer of saving the soil water and 

 minimising losses by evaporation, yet one of the funda- 

 mental acts of husbandry in the spring consists in roll- 

 ing and otherwise consolidating the land. Particularly 

 is this the case on the chalk and similar light soils ; when- 

 ever a spell of dry weather prevails in the early part of 

 the year the farmer will be observed rolling his seeds, 

 or his spring corn, or his newly sown turnip land, as 

 the case may be ; he will even take a heavy cart 

 wheel down between the drills when the roller will 

 not give him pressure enough. The result of the 

 consolidation of the surface soil thus effected is to 

 improve its power of lifting the soil water from below 

 by capillarity, because the pore space is diminished 

 and the wide intervals across which the water film 

 cannot exist are largely closed up ; just as the motion 

 of water through surface tension almost ceases in a 

 thoroughly loose soil, it is, per contra, increased when 

 the particles are brought more closely together. 

 Hence, on the rolled land there will be a greater lift 

 to the evaporating surface and subsequent loss of 

 water, but the farmer faces this loss in order to keep 

 the upper few inches of soil supplied with moisture. 

 Rolling is only done on land occupied by germinating 

 seeds, young spring corn, or a young ley, where the 



