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CHAPTER VIII. 



Beneficial Effects of Vegetation on Soils after Drainage Action of Drains in 

 Light Soils Action of Drains on Retentive Soils Smith's System 

 Elkingtou's System Advantages of Drainage Improvement of Land by 

 Trench Ploughing Sub-soiling Clay-Burning Claying Marling 

 Chalking Warping Ordinary Cultivation. 



WITHOUT reverting to the various reasons why land drain- 

 age is beneficial, there is one important point which has been 

 omitted, namely, the action of vegetation, which no doubt 

 tends to modify soils and to improve them after they have 

 been freed from surplus water. The free ingress of the air 

 has been mentioned, and the oxidizing effect which it exerts 

 not only upon sour matters in the soil, but especially on sour 

 matters in the sub-soil ; the effect being, as was pointed out, 

 pulverization of the sub-soil as well as of the soil, and that 

 down as far as the depth of the drains. So that if we imagine 

 the case of a thoroughly stiff soil resting upon a thoroughly 

 stiff sub -soil, the tendency after thorough drainage is to 

 modify, pulverize, and oxidize the whole of the section of 

 sub-soil above the drain, and to cause it to assume in some 

 degree the character of a free soil. Now it is just at this 

 point that the action of vegetation comes in ; the roots have 

 freer ingress as well as the air ; the altered and improved 

 ndition of the soil increases the depth available for plants, 

 d we have not only pulverization taking place, but the 



rmeation of the ground by vegetable roots, which as they 



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