54 LAND DRAINAGE 



DRAINAGE EFFECTS 



The steps in soil improvement to be expected from 

 proper tile drainage are summarized in the following para- 

 graphs. They are presented here to bring the facts into 

 perspective. 



77. Effects of the permanent removal of standing water. 

 It has been shown that no matter how excellent the 

 structure of a soil may be, the excellence cannot be main- 

 tained if the soil is subjected for a time to a state of satura- 

 tion. It has been shown why, and to what an extreme, the 

 packing or puddling may proceed under such adverse 

 moisture conditions. It might seem that where the clay 

 loams and clays have been subjected to the presence of 

 standing water for years, or even throughout the major 

 part of each year for a series of years, the soils would be- 

 come so compacted as to render it impossible to develop 

 in them the physical conditions so essential to crop pro- 

 duction. This, however, is not the case. The rapidity 

 with which these desirable physical conditions develop, 

 after provision has been made for the quick removal of 

 all gravitational or standing water, is frequently surprising. 



78. The way in which the changes take place. When 

 the ground water is permanently lowered to three or four 

 feet below the surface, where previously it stood almost 

 permanently at or near the surface, one of the first 

 effects of the lowering is the development of many cleav- 

 ages or cracks, such as are seen in Fig. 21. These cleav- 

 ages occur because of the shrinking of the soil as it gives 

 down the excess of water filling its pore space. This 

 statement may seem to contradict the statement in para- 

 graph 67 concerning the degree to which the pore space 

 is reduced in persistently saturated soils. All saturated 



