628 SOILS: PROPERTIES AND MANAGEMENT 



subsoil ; and the tendency of the soil to puddle and bake 

 when dry. When the wetness is prolonged, the accu- 

 mulation of organic matter in the surface soil imparts a 

 dark color. Poor drainage causes a mottled color in the 

 subsoil, and in extreme cases a pale gray color resulting 

 from excessive leaching. When the land is in crops the 

 wet places are recognized by their miry condition in early 

 spring and after rains, and by the slow starting of the 

 crop. In meadows the grass is often winterkilled, leaving 

 only those weeds that can withstand the conditions. 

 Heaving of soil is another indication of wetness. In tilled 

 crops the wet spots are often marked by the small growth 

 of the plants and by curled, wilted leaves in dry periods. 

 In orchards weakened and missing trees are in many 

 cases an indication of defective drainage, especially in the 

 subsoil, where the roots of older trees seek to develop. 



Steeply sloping hill land may need drainage quite as 

 much as flat land if it has a compact subsoil overlaid by a 

 porous topsoil. Water is then trapped in the soil, and is 

 removed very slowly by percolation on top of the hard 

 subsoil and by evaporation. It is wet land in need of 

 drainage. 



531. Extent of drainage needed in humid regions. - 

 The amount of farm land in need of some drainage is very 

 large. Besides the land commonly designated as swamp 

 and marsh, there are very large areas of land devoted to 

 crop production, the yields from which are reduced by the 

 excess of water that they contain at certain seasons of the 

 year. The extent of swamp land varies in different coun- 

 tries, but is likely to aggregate about five per cent of the 

 total area. The cropped land in need of some drainage is 

 very much larger, and roughly aggregates three-fourths of 

 the tocal improved land surface. The temporary wetness 



