OTHER CONDITIONS AND PROBLEMS 



159 



to collapse. One considerable area of muck soil on the 

 Michigan Agricultural College farm had so seriously settled 

 in this way in twelve years, that the tile in the whole area 

 had to be relaid. Except where truck-farming is prac- 

 ticed, therefore, tile should be laid more than three feet 

 deep in muck soils, if outlet conditions will permit. 

 210. Gravitational water in irrigated lands. Much 



FIG. 68. Plan for moving surface water by way of silt-basin and the 

 tile system, adapted from Bulletin No. 199, Wisconsin Agricultural 

 Experiment Station. 



has been said and written of the injury done to lands by 

 seepage waters. It has almost invariably been charged 

 that these waters, coming from higher areas, where they 

 have been used in excess to water lands, or by seepage 

 from supply canals, passing down or out to lower areas, 

 become charged with alkali salts ; that, as they come to 

 the surface of these lower areas, and evaporate, they leave 

 their burden of salts to incrust the surface and later to 

 work injury or death to crops planted thereon. In 1890 

 Shaler described the destruction of the very fertile area 



