TMK MOlSirKK IN THK SOIL 



()1 



hftnl upon the Hiirfiioi' that tin* water of riiiiifall iievtT can pUHH 

 <lu\vn. By placing th<« drains t>liallo\v, the soil is rendfri*«l nicllow 

 and p<irous, water passes down readily, the level of free water is 

 raised, and the surplus is removed. 



7G/>. Tile distanee apart at whicli drains should l.e placed is 

 varialde, l>ut HO feet is usually eonsidercd most advisalijc. The 



FiK I' !• 



■ Ic i>|«"ii (litph. 



level of the free water tends to rise higher at a point midway 

 between drains, as shown in Ki^. 8. If the drains are tot. far 

 apart, this tendency may l>e jjreater than the tendency to move 

 toward the drain. In soils through which the water moves some- 

 what readily, the tirains may be farther lemoved than in close, 

 impervious soils. 



7S<i. In the sprint;, on tnidrained soils, free water remains 

 for a considerable time near the surface: consequently the plant 





Vxu 1 1 SliteK IfNj Dle^p. 



roots cannot penetrate deeply into the soil. When the droupht 

 conns the surface is fii-'*t afTt«cte<l, and the plants suffer at once. 

 It is n well-known fact that tap-rooted plants are admimbly 

 fitted to withstand «lr>- weather. Their feetlers are deep in the 

 soil. It is this condition which is obtained to n certain extent liy 

 underdrninnjfi-. The soil a>>ove the drain is made porous, the 

 wafer which cannot W held by capillarity is quickly removed, the 

 air penetrates, the s«>il becomes warm and oonirenim Fhiis 



