48 Effective Farming 



Under drainage. Usually in underdrainage, short sections 

 of burned clay tile are placed end to end in a ditch which is 

 immediately filled with earth. Thus the land above the tile 

 can be farmed. Before laying the tile, the bottom of the ditch 

 is smoothed and accurately graded. The water enters the 

 tile through the joints and, encountering a smooth channel, 

 flows to the outlet. Tile drains operate best if the grade is 

 one or two feet in a hundred, but they will operate satisfactorily 

 if the grade is only three or four inches in a hundred feet, pro- 

 vided it is uniform. The depths of drains should be from two 

 feet for a clay loam or other moderately heavy soil to three and 

 one-half feet for an open soil like a sandy or gravelly loam. 

 The penetration of roots in clay loam is less deep than in the 

 more open soil. The distance between the drains is governed 

 largely by the kind of soil and its wetness. For general farm- 

 ing, there should never be more than one hundred feet between 

 the drains ; if the soil is heavy and badly in need of drainage the 

 distance should be much less. The outlet of the ditch usually 

 requires protection. The tile here are often exposed and, to 

 avoid breakage, a length of iron pipe can be used advanta- 

 geously in place of the last few tile or the outlet can be pro- 

 tected by a wall of masonry. 



24. Air in soil. Oxygen, carbon dioxide, and nitrogen of 

 soil air are needed in plant growth. Oxygen must be pres- 

 ent, as seed will not sprout nor plants grow without it. A 

 soil saturated with gravitational water does not contain oxy- 

 gen, because the water has crowded out the air and occupies 

 all the pore spaces. A plant kept even for a relatively short 

 time in a water-logged soil will die for want of oxygen about 

 its roots. Water standing on a field for even a few days is 

 likely to result in the loss of the crop. 



The oxygen is also needed for the oxidation of the organic 

 matter in the formation of humus. If this did not take place 

 in the soil, there would soon be more undecayed organic matter 

 than live plants on the earth. A sod turned under in a soil 



