LAND DRAINAGE 33 



form, from which crop roots are chiefly supplied. In fact, in 

 such regions from one-fifth to more than one-half of the rainfall 

 ultimately drains into the streams. 



On any soil of a dense structure, such as clay, and on loamy 

 and lighter soils having a compact sub strata, and also where 

 the soil may be loose and porous, but shallow, due to the near 

 approach of bed rock, this surplus water is held too long in the 

 root zone near the surface of the soil. Such land needs drainage. 

 This condition may, and frequently does, occur on quite steep 

 slopes. A hillside is no guarantee that good soil drainage exists. 



Another type of wet land is of the springy sort. For one 

 reason or another, the general underground flow of this surplus 

 water is brought to the surface by some impervious strata and 

 appears as springs of greater or less persistence and value. No 

 fixed rules for their occurrence can be laid down beyond that 

 already stated. The observations and experience of the average 

 individual will indicate to him that they may occur on a broad 

 flat as well as on a hillside or in the more common position at 

 the foot of a slope. 



Then there is the wet land due to the overflow of streams at 

 periods of high water and the land that is wet because it is so 

 near the level of the surface of the water in some adjacent 

 stream, pond, lake or even the ocean; for there are thousands 

 of acres of tidal marsh land. Wet land may be divided into two 

 general types, namely (a) swamp or marsh land and (b) mod- 

 erately or intermittently wet land. 



Extent of wet land. — The total area of wet farm land in the 

 United States is very large. Swamp and marsh land aggregates 

 something like twelve thousand square miles, or upwards of 

 seventy-five million acres. The very much larger area of wet 

 land falls in the second or intermittently wet group. This area 

 is included in farms and is more or less under cultivation. East 

 of the eastern line of Kansas the area of farm land now being 

 cultivated that is giving inadequate returns because of poor 

 drainage aggregates several times the area of swamp and marsh 

 land. Every farmer should understand that his first problem is 

 to drain this wet land on which he is expending money for labor, 

 materials and interest to grow poor crops. This is the really big 

 farm drainage problem in any part of the world having a rain- 

 fall similar to the eastern half of the United States. The inter- 

 mittent wetness of such land is even more injurious than is con- 

 stant wetness because it results in wider extremes of moisture 

 supply to the crop. 



