CHAPTER IV 

 DRAINAGE AND IRRIGATION 



From what has already been said it is clear that the mois- 

 ture in the soil is an important item. If a soil has too much 

 moisture we try to get rid of the surplus by drainage; if it 

 has too little, we apply water to the soil, that is, irrigate it. 



Kinds of Drains. — All drains may be grouped in two 

 classes — open and closed drains. Of the open drains we have 



(1) the surface drain, made by plowing a furrow up through 

 the low place in a field to allow the water to run away. 

 Sometimes these surface drains are made by plowing the 

 field in narrow *' lands," thus having many *'dead" furrows. 



(2) The open ditch. This differs from the open drain only 

 by being wider and deeper. The surface drain lasts only one 

 year or until the field is plowed again. The open ditch lasts 

 usually for several years. Muck beds are often drained by 

 open ditches. In many parts of our country there are large 

 open ditches put through by the authority of the county or 

 state. These extend for miles in length and serve as an out- 

 let for all other kinds of drains. They are frequently called 

 county ditches. Sometimes they are called dredge ditches, 

 because a dredge has been used for removing the dirt and 

 making the channel. 



By closed drain or under-drain is meant that kind of 



drain in which a trench or ditch has first been dug and some- 



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