EVAPORATION FROM BARE SOIL 115 



water present determined. If we look at the mean water 

 contents of the soils in the five weeks in the summer when 

 the untouched soil was driest, we shall perceive most clearly 

 the effect of these various attempts to preserve the water 

 in the soil. The average water contents in the driest portion 

 of the season was as follows : 



Water per 100 of Dry Soil 



Untouched Soil. Surface k%)t stirred to : Oat Straiv. 



half an inch, two inches. four inches. one inch. 

 16-9 ... 19-0 ... 19.2 ... 20.3 ... 22-8 



Thus keeping only half an inch of the surface stirred had 

 a very distinct effect in preventing evaporation. The effect is 

 increased, but not very greatly, by a deeper stirring. The 

 maximum result is gained by the mulching with straw, one 

 inch of straw proving far more effective than four inches of 

 loose soil. The excess of water in one foot of the mulched 

 soil was about equal to one inch of rain, and the influence of 

 the mulch would doubtless be felt in both the second and third 

 foot. Mulching should not be too deep, else slight showers 

 will be retained by the mulch and never enter the soil. 

 Mulching has the further advantage of effectually preventing 

 the puddling of a clay soil by heavy rain. 



The accumulation of dead leaves, seed vessels, &c., upon 

 the soil of a forest, is of great importance to the fertility of the 

 land, and its maintenance is one of the cares of scientific 

 forestry. One of the benefits derived from this layer of forest 

 litter is a diminution in the evaporation from the surface ; it 

 acts in fact as a natural mulch. Ebermayer, in the experiments 

 already referred to (p. in), found that the evaporation from 

 an artificially saturated soil within the forest when covered by 

 litter, was in the summer months only 46 per cent, of that 



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