SOIL IMPROVEMENT 8/ 



and need only to have the surplus water removed to make them very 

 productive. 



Benefits of Drainage. Let us consider some of the ways in 

 which drainage benefits soils and crops. 



First: Drainage gives plant roots more room. The roots of few 

 agricultural plants can penetrate airless, water-filled soil. As 

 water is drawn off, air is admitted. The plants are not drowned 

 by standing water in wet weather ; in dry weather they have the 

 advantage of larger areas from which to collect food and water. 



Second: Drainage makes the soil warmer. In wet soils a large 

 part of the heat waves are used to convert the surplus water into 

 vapor. On these cool, wet lands, plants grow slowly. Drainage 

 lessens evaporation by drawing off the surplus water; it also warms 

 the soil by admitting air. 



Third: Drainage, by warming the soil and admitting air, favors 

 processes which produce plant food. As you learned, bacteria 

 which prepare nitrogen for plant use work best in varm, rich, 

 moist, well-drained soils. In wet, ill-drained land, bacteria thrive 

 which destroy nitrogen and form acids injurious to crops. 



Fourth: Drainage, by drying the soil, makes it workable earlier 

 in the spring. Crops can be planted earlier, and thus" get the benefit 

 of a longer, and usually of a more favorable, growing season. 



Fifth: Drainage prevents washing on light and rolling land. 

 The particles of such soils do not adhere closely, and heavy rains 

 carry away the plant food and even the soil itself. Have you 

 not seen thin, unproductive hillsides scarred with gullies ? Fring- 

 ing these hills is often a rank growth of weeds and briers, which 

 shows where their fertility has gone. 



Methods of Drainage. Sandy and light soils are naturally 

 drained, unless the water table is near the surface. Clay soils 

 and those with clay subsoil often need artificial drainage. 



