24 BULLETIN 995, U. S. DEPARTMENT OF AGRICULTURE. 



ditches will run lengthwise of the field, thereby avoiding the crossing 

 of the ditch in the usual farming operations. The size and depth of 

 the open ditch will depend upon the length and fall of the ditch, 

 the location of the subsoil, the amount of water to be carried, and 

 the position of the outlet. The drainage ditch should always be deep 

 enough to prevent any interference of the water table with the crop 

 to be grown. 



The Mind ditch. — The most satisfactory method of artificial drain- 

 age is the blind ditch. In the construction of this ditch tile is used 

 most commonly. Many fields that otherwise would not yield profit- 

 able crops have been reclaimed by the blind ditch. These ditches 

 should be laid out very carefully with reference to direction, depth, 

 and slope, so that the entire area under consideration will be drained 

 thoroughly. The size of the tile is very important. Tiles that are 

 too small must never be used. This is false economy, and it fre- 

 quently results in added expense in that the small tiles must be taken 

 up and replaced with larger ones. The tile should be large enough to 

 carry off the water quickly in times of excessive rainfall, deep enough 

 not to be disturbed by the plow or other implements, and laid so 

 carefully that the ends will fit against each other evenly and a gentle 

 and continuous fall should be provided, without depression or ele- 

 vation. The outlet of the blind ditch should be kept open, that the 

 water may flow freely. 



SEEPAGE. 



Seepage is closely related to drainage. Many fields or areas that 

 otherwise might be profitable for crop production are rendered use- 

 less by seepage. This is especially noticeable in those areas where 

 irrigation is practiced. Seepage is detrimental to the soil in several 

 ways : (1) As a loss of water, especially in cases where water has been 

 stored for irrigating purposes, and (2) through a loss of the use of 

 the land, either because the soil is too wet for crop production or be- 

 cause of the accumulation of soluble minerals which are brought to 

 the surface through seepage. The injurious soluble minerals usually 

 are known as alkali. 



Seepage from streams. — Some streams are so located naturally 

 that a portion of the water seeps into the adjacent soil, form- 

 ing marshes or waste places due to excessive moisture; this is 

 especially true Avhere the fields adjacent to the stream are low, 

 level, or underlain with an impervious subsoil. The nature of the 

 bank of the stream is of importance in this connection. If the 

 overflow at flood time is prevented by the construction of dikes the 

 land may be made productive by drainage. Usually these marsh- 

 lands when drained are very fertile and produce good crops, though 

 they are not always the best for sugar-beet production, since they 

 sometimes produce large roots low in sugar. 



