66 LAND DRAINAGE 



years ago the drainage waters were removed by gravity 

 through sluice gates in the dike opened at low tide. The 

 shrinkage of these marine marsh soils is considerable, and 

 it is probably only a matter of time when pumping sys- 

 tems for removing the drainage water must replace the 

 gravity systems already installed. 1 The rate at which 

 the saline materials disappear from these soils, after an 

 effective drainage system is installed, is rapid. Shaler 

 says, " These changes will spontaneously take place in 

 the course of 3 to 5 years after the sea is excluded from 

 the marsh, but by breaking up the surface with a plow 

 and cutting frequent ditches through the plain, a single 

 year will often suffice to bring the soil into the state where 

 any of our domesticated plants will grow upon it." 2 



95. Economic oversights. Where large areas of land 

 are wholly or largely submerged or saturated, the necessity 

 for drainage is apparent, and effective reclamation methods 

 are applied. The land is thus brought at once to a rather 

 high degree of agricultural efficiency. But there are at 

 least two classes of soils whose service is partially or 

 wholly lost to actual crop production. 



96. Areas of imperfect natural drainage. The first 

 class includes a large number of areas of soil, ranging in 

 size from a fraction of an acre to many acres, which are 

 saturated or submerged a sufficient period each year 

 seriously to affect the physical structure of the soils, and 

 therefore directly, or indirectly, to affect all their other 

 important physical conditions temperature, ventilation, 

 and capillary moisture capacity. The over-wet condi- 

 tions usually occur in the spring and thus interfere with 



1 Bulletin 240, Office of Experiment Stations, U. S. Depart- 

 ment of Agriculture. 



2 Shaler, 12th Report U. S. Geological Survey, Part 1, p. 321. 



