WATER CAPACITY OF SOILS. 



147 



old, 24.79 percent; spruce 60 years old, 23.39 per cent; spruce 120 years 

 old, 30.01 per cent; naked soil, 22.39 per cent. 



Hence, take it altogether, the naked soil contains considerably less 

 water than the forest-covered soil. But the distribution of the water 

 through the difterent layers of the soil is different in the two cases; the 

 naked soil, due to rapid evaporation, no doubt, contains the least 

 amounts in its upper strata, where the forest soil with its absorptive 

 coA'cr preserves the largest amount. Measurements of the stratum 

 from 2 to 6 inches would probably have shown the preservative effect 

 still more prominently. 



The water capacity of soils and soil covers in general has been re- 

 ferred to as an element of interception. With reference to the run off, 

 this capacity becomes influential in determining the manner of run-off". 

 As soon as the soil cover and the upper soil strata are saturated, and 

 especially when the latter are more or less impermeable and the rain 

 continues, either uo water or only a small part gradually can find en- 

 trance into the soil, and the run off" becomes in the main suiierlicial, or, 

 if the ground be not slo])ing, stagnant water results. 



For every watershed, no matter what its conditions, there may, there- 

 fore, come a time when the rain or snow-melting continuing, the entire 

 run off becomes superticial, the soil being unable to take up more. 



It is evident that this time must occur later in the forest than on 

 the unfoiested and especially naked soil, because the water capacity 

 of the soil cover as well as of the protected soil in the forest is greater 

 than that of the naked soil or that covered with field crops. 



The water capacity of litter, which Wollny investigated, depends on 

 its nature and, of course, its thickness to a certain degree, and is quite 

 considerable, much greater than that of soils. 



The water capacity of various litters was found to be as follows in 

 volume per ceut: 



No soil cover was found so variable in water contents as moss, while 

 litter would hold two or three times as much water as moss and twice 

 as much as the soil. 



The variation of water capacity at dififerent depths appears from the 

 following figiues : 



