n6 RELATIONS OF SOIL TO WATER 



from a soil similarly circumstanced but without litter. Taking 

 the evaporation from a saturated soil during the six summer 

 months as 100 outside the forest, it amounted to 47 within the 

 forest, and to 22 when the soil within the forest was covered 

 by litter. The moss which covers the ground in pine forests 

 when light gains access, acts equally as a mulch. It may, 

 however, become injurious if it attains too great a thickness. 

 Rain is then retained by the moss instead of entering the soil. 

 The forest litter of dead leaves, &c., does not become injurious 

 by accumulation, as it forms by decay a new surface soil in 

 which the roots of trees distribute themselves. On a steep 

 hill-side both moss and leaf-litter discharge another beneficial 

 function, retaining the water of heavy rains which would else 

 be lost. 



The effect of tillage on evaporation has been already partly 

 discussed. Any loosening of the texture of the surface soil 

 favours the more rapid drying of the disturbed layer, but 

 may, as we have seen, preserve the store of water beneath. 

 When tillage is performed with this end in view the layer of 

 soil loosened must be shallow ; any deep tillage in summer 

 time is out of place if the preservation of soil water is an 

 object. 



The effect produced by rolling after harrowing requires 

 some notice. Rolling consolidates the soil, and the result is 

 that for a time the quantity of water at the surface is 

 increased. It is obvious that the consolidation of a loose soil 

 increases the quantity of water in a given volume. By rolling 

 the surface soil is also brought into more intimate contact 

 with the moist subsoil, and the transference of water becomes 

 easier. Moreover we have just seen that a solid soil does not 

 become dry at the surface so quickly as a loose one, owing 



