246 CROP PRODUCTION 



free water of the soil. Such free water fills the pores 

 between the soil particles, and unless there is natural 

 or artificial drainage, it is likely to remain and keep the 

 ground so wet that the soil becomes stagnant and then 

 the roots of most plants cannot grow. Consequently, 

 in productive soils there must be either natural or 

 artificial drainage to permit this free water to run away. 



The great majority of sandy and loamy soils are so 

 situated that there is natural drainage by means of which 

 the free soil water seeks lower levels without help from 

 man. But in many clay soils, and in other soils which 

 are underlaid by hard pan, it is necessary to provide 

 artificial drainage to lower the level of this free water 

 in the soil. The simplest way to provide drainage is to 

 dig through the middle of a field a ditch deep enough so 

 that the water will readily be carried away. This ditch 

 may be left open, but in this case it takes up much room 

 and is inconvenient. A better plan is to lay drain 

 tiles along the bottom of the ditch and then fill in the 

 ditch with earth over the tile. This is called tile drain- 

 age, and it is the best method of improving wet soil. 



Such soils are improved by tile drainage because the 

 surplus water runs away quickly, leaving the pores be- 

 tween the soil particles open to air and root growth. 

 Consequently, the field can be worked earlier in spring, 

 so that the crops get an earher start -and the roots go 

 deeper. 



Capillary Moisture 



If you take a handful of soil from a drained field and 

 squeeze it tightly, you are likely to find that it is quite 

 moist. Obviously the free water in the soil in this case 



