AGRICULTURE AND RURAL ECONOMY. 537 



noted that in a loose soil a great deal of water may evapo- 

 rate from points below the top. Commonly, the looser the 

 soil is, the more surface will it expose to evaporation. 



Effect of Loosening the Surface of the Soil upon Evaporation. 



The above considerations help us to understand better 

 why it is that, as Nessler has shown, " the general opinion 

 that a loose soil dries faster than a compact one is not al- 

 ways correct. There are two processes to be distinguished: 

 in the first place we have the evaporation from the top of the 

 soil, and in the second place that from layers below the top. 

 Loosening the top of the soil helps the second process by ex- 

 posing more surface to the air, but it may hinder the first 

 process by decreasing capillarity. With loose materials, like 

 a sandy soil, cultivation, while increasing the surface, might 

 not decrease capillarity very much, and so might increase 

 evaporation. 



" In the majority of cases, however, loosening the upper 

 layers seems, so far as experiments have been made, to de- 

 crease the rate of evaporation by decreasing capillarity. ISTot 

 only would the water be transmitted less readily by the loose 

 portion, but it would pass with difficulty from the fine in- 

 terstices below to the laro;e ones above. 



" Loosening the upper layer would seem likely to affect 

 especially a soil composed of porous materials, or one which, 

 like a clay, is broken up by tillage into porous fragments, by 

 decreasing the number of points of contact." 



Influence of Hoeing and Rolling the Soil. 



In the article on the present status of agricultural physics, 

 elsewhere referred to, Von Liebenberg discusses the effects 

 of the use of the hoe and the roller upon the moisture in 

 the soil, and concludes that " hoeing, although confined to 

 the surface, tends to retain the moisture in the soil ; rolling, 

 to remove it two facts which, though apparently in conflict 

 with the ordinary assumption in practice, are, nevertheless, 

 true. The advantages of rolling are incontestable, and the 

 roller cannot be dispensed with, only its good effect does not 

 depend, as is commonly held, upon its holding the water in 

 the soil. In most cases, aside from those in which it is used 

 to break down lumps and even-off the ground before drill- 



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