110 



LAND DRAINAGE AND IRRIGATION 



The free movement of air, possible only in a well-drained soil, 

 aids materially in warming it. 



The most effective soil-warming agent is warm rain water. 

 We all know how quickly the dormant vegetation starts growing 

 in early spring when a warm rain sinl<:s mto a well-drained soil. 

 Water-logged soils are not benefited in this way by warm rains, 

 because all the rain water is forced to run away as surface water. 



■=^->fe 





-^--i-^Trt^rccie^rSo//- 



A 





Fig 45 — A crop on a well-drained soil has a better moisture supply than when planted 

 on a wet soil A, diagram showing root development m a wet soil W, high water-table, 

 B, diagram showing root development m the same soil but tile drained, T, tile, M, lowered 

 water-table (Page 95 ') 



2. Roots Grow Deeper and Stronger. — Plants growing in soils 

 that are wet oi; water-soaked develop shallow root systems (Fig. 

 45). Marsh grasses and tamarack, for example, are shallow 

 rooted. Corn and other crops will not send their roots into a 

 water-soaked subsoil, but will develop them near the surface. 

 Drain a marsh, and the wild grasses and the tamarack die, because 

 the surface soil dries out, and the shallow roots are left without 

 water — capillary rise not being rapid enough to supply sufficient 

 moisture from lower depths. This helps to explain why corn 

 planted on land that is wet during the early growing period suffers 

 for want of water during the simimer when the land becomes dry. 

 It seems strange, but it is true, that crops are able to get a better 



