Land Drainage and Soil Efficiency 



1823 



4. Drainage results in a higher average temperature of the soil and 

 in a quicker warming in the spring. The difference in warmth between 

 sandy and clay soils is due to their different capacities to hold water. 

 Either kind of soil is cold, and slow in becoming warm, when saturated 

 with water. A low temperature hinders the starting of seed and the 

 growth of plants. A drained soil will probably be eight or ten degrees 

 warmer than the same soil undrained. 



5. The supply of available plant-food is increased by the better ven- 

 tilation, higher temperature, deeper root penetration, better tilth, better 

 moisture supply, and more active and favorable bacterial growth in 

 the soil — all of which conditions result from improved drainage of a wet 

 soil. The organisms that cause the decay of roots and manure and those 

 that use the free nitrogen of the air are particularly affected in a beneficial 

 way. All these benefits help to reduce the need for commercial fertilizers, 

 thereby effecting a material saving to the farmer, which saving goes on 

 from year to year. 



6. The winter heaving of plants is largely prevented by drainage. 

 Heaving is due to the freezing of water in a saturated soil. Water 

 in freezing expands, and, since in the process it cannot expand in any other 

 direction, expansion is manifested by a lifting of the surface. The frozen 

 soil carries small plants with it. When the ground thaws the soil falls 

 back around the roots of the plants. Each time the freezing is repeated, 

 the heaving is in- 

 creased; and on wet 

 land in some seasons, 

 tap-rooted plants, such 

 as clover, may be raised 

 to the extent of twelve 

 or fifteen inches, and 

 literally spewed out of 

 the soil and left on the 

 surface to dry up. All 

 winter crops are partic- 

 ularly subject to this 

 type of injury, which 

 is frequently called 

 "winterkilling." Wet- 

 ness of the soil is its cause and drainage its remedy 



Fig. 46. — Area of land nearly level, but having compact 

 subsoil with undulating subsurface, thereby causing wet 

 pockets that force plants to form short roots. Weeds 

 are abundant in such areas. Drainage removes the water 

 and permits deeper penetration of the plant roots, thtis 

 enlarging their feeding zone 



PURPOSE OF DRAINAGE 



The object of drainage is to remove quickly from the root zone of the 

 soil the excess of water above that which may be retained in thin films 



