524 IOWA DEPARTMENT OF AGRICULTURE. 



regarding drainage operations. This lack of definite information is a 

 serious drawback to the drainage of lands which would be immeasurably 

 improved by the removal of surplus water. 



Therefore we have endeavored to collect from various sources, facts and 

 suggestions regarding the drainage of clay, gumbo, muck and peat soils. 

 Soils of these classes are found in large areas in Iowa and the drainage of 

 these tracts is a work of the greatest economic importance. 



For ordinary farm crops it is not often necessary to lower the soil water to 

 a depth to exceed four feet. Frequently the lowering of the water table 

 may be less. Experiments have shown that the roots of winter wheat, bar- 

 ley and oats penetrate a heavy clay soil and subsoil to a depth of fully four 

 feet. In the same type of soil the roots of the corn plant reached an equal 

 depth. Therefore it is usually deemed advisable to place tiles at a depth of 

 three and a half to four feet. Unless this is done it is impossible to put the 

 soil in the best condition for crop production from the standpoint of circula- 

 ion of air, the activity of the soil bacteria and the most favorable moisture 

 conditions. 



All sandy and loamy soils are readily drained and rarely present trouble- 

 some problems in regard to the depth or distance apart of drains. It is well, 

 however, to note the following facts in regard to the drainage of sandy and 

 gravelly soils. Water percolates readily through sand or gravel, but there 

 are a few cases when such lands require drainage. A basin-like area of 

 sandy soil frequently is found where the surface soil rests upon clay. In 

 such a case adequate drainage is essential aud can usually be secured by 

 the judicious use of a few deep drains. Further, where the top soil is under- 

 laid by a sandy subsoil, tile should not be placed so as to draw the water far 

 down into the sand because in this type of soil the force of capillarity can 

 not carry water upward rapidly but a short distance. We have conducted 

 laboratory experiments which conclusively prove this point and it is one 

 which must not be overlooked in the drainage of sandy soils. Again, if the 

 ground water surface is carried below the limit of rapid capillary movement 

 not only is there a reduction in the amount of ground water available for the 

 crop, but there is also a reduction in the amount of summer rainfall which 

 the crop can make use of, owing to the fact that when heavy rains occur a 

 considerable portion of the water which is thus brought to the soil percolates 

 downward beyond the limit of the root zone before the crop is able to 

 utilize it. 



In contrast with the open, porous, sandy and gravelly soils, we have the 

 compaot clay through which water seems scarcely to percolate at all. But 

 the fact that the clay has water in it makes it evident that this soil is not 

 really impervious to water and therefore can be drained successfully. About 

 the only soils we may properly term impervious are those which have been 

 puddled. In brief, any soil which has been exposed to air, water and frost, 

 is permeable to water to a greater or less degree and hence we may conclude 

 that the upper stratum of practically any soil will allow water to pass through 

 it to such an extent that a drainage system which has been properly installed 

 will prove effective in time . 



Many landowners question the wisdom of tiling tenacious clay soils to a 

 good depth. Our study of this subject leads to the conclusion that there is 

 ample evidence to justify the drainage of even the stiffest clay soils. If time 



