LAND DRAINAGE 638 



of too much moisture in the soil in proportion to its 

 pore space. When water freezes it expands one-eleventh 

 of its volume. If the soil is too nearly saturated, this ex- 

 pansion is expressed at the surface of the soil by a lifting, 

 or heaving, which is exceedingly injurious to most crops 

 that pass the winter in the soil. It breaks their roots 

 and gradually lifts the smaller plants out of the ground 

 if the process is many times repeated. When the soil is 

 drained so that free air spaces are distributed through 

 the mass, the expansion of the water as it freezes is taken 

 up in these spaces without heaving at the surface. 



11. Drainage reduces erosion of soils by withdrawing 

 the water through the soil instead of permitting it to 

 accumulate to the point where it must move over the 

 surface, often with serious erosive action. In order that 

 the drains may be efficient, the soil above the drains must 

 be sufficiently porous to permit the removal of the water 

 as fast as it accumulates. 



12. Thorough soil drainage greatly increases the effi- 

 ciency of all equipment and practices used in crop produc- 

 tion on the farm. There is a longer time in which to do 

 the work, a longer season in which the crop may grow, 

 and usually less labor is required in order to fit the land 

 and keep it properly tilled. Further, the crop matures 

 more evenly and is likely to be of better quality. The 

 need for a commercial fertilizer is reduced because of the 

 higher efficiency of the soil. 



13. Prompt and thorough drainage of a wet soil results 

 in a large increase in yield and quality of crops. All the 

 common farm, garden, and orchard crops are injured by 

 a saturated condition of the soil, and the changes that 

 accompany the correction of that condition permits a 

 large growth of the plants. The fundamental nature of 



