106 TILLAGE— MOVEMENTS OF SOIL WATER [chap. 



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 

 roots, if any, are so close to the surface that the whole 

 crop will perish if the top layer is allowed to dry. The 

 effect of rolling is to increase the capillary lifting power 

 of the top soil, so maintaining it in a moister condition, 

 although the land as a whole is made dryer by the extra 

 evaporation which must accompany the rise of subsoil 

 water to the surface. It is a maxim in farming on the 

 chalk, where there is always a store of subsoil water at 

 some depth or other, and where also the surface soil is 

 peculiarly liable to become open in texture through the 

 action of worms and the rapid decay of dung, that the 

 land will become moist if it can only be got "tight" 

 enough. On any light cultivated land it is easy to 

 notice how much moister the soil remains when it has 

 been consolidated by a foot mark ; a gardener again, 

 whose rich and deeply-worked soil is apt to get very 

 open, always treads the ground as solid as possible in 

 preparing a seed bed for onions and other small seeds. 

 The following figures given by King as mean values 

 from a number of measurements show how rolling dries 

 the soil as a whole when samples are taken down to 2 



