92 WATER IN SOILS 



ture makes them all the more thrifty. Truck crops, orchards and 

 other fruit plantations usually thrive better under such protection. 



One objection which is often raised to the growing of wind 

 breaks near fields or crops is the drying effect of the trees on the 

 soil very near them. This is sometimes prevented by digging a 

 trench two or three feet deep between the trees and the growing 

 crop. This should be a few feet from the tree trunks. Surface 

 roots are thus cut and prevented from drawing moisture from the 

 soil beyond the ditch. The roots of trees will send out many 

 fibrous branches where they have been cut, and it will require 

 several years for them to draw moisture from a distance beyond 

 the ditch. Of course the ditch is not left open. It may be reopened 

 every five or six years and closed immediately. By this method 

 the roots of the growing wind break are turned and the moisture 

 is conserved for the use of the money crop. 



In prairie countries the wind break may be made wide enough 

 to produce a crop of its own. Such may be made wide shelter 

 belts and produce timber for posts, poles, lumber and fuel. It is 

 believed that such shelter belts will be profitable in themselves, 

 aside from the benefits they give to the adjacent cultivated fields. 



FIELD AND LABORATORY EXERCISES 



1. Distribution of Rainfall. Obtain weather reports covering your region 

 and find the average annual rainfall. In what months does most of the rain 

 occur? What are the dry months for your section? What years in the last 

 ten have been considered wet years and what ones were dry years? If the hot, 

 dry months are during the growing season, what is the conclusion regarding 

 the need of saving moisture in the soil? 



2. Depth of Water Table. During the wet season of the year dig a post 

 hole in the field or yard and determine, if possible, the depth of free water. 

 Protect the post hole from being filled up by placing a board or flat stone over 

 it. From time to time examine and see if the free water has disappeared or 

 has reappeared during the changes of weather. 



3. Capillary Action of Soils. Compare two samples of soil in their capil- 

 lary action. Use sand for one and clay for the other. Place them in two lamp 

 chimneys, with a cloth tied at the bottom of each to hold the soil. Place both 

 at the same time in a dish of water and note the rise of water in each. Is this 

 water climbing in the soil capillary water, free water or hygroscopic water? 



4. Moisture in Dust. Take a sample of dry road dust. Put it in a test 

 tube. Place a little wad of paper in the mouth of the tube to partially exclude 

 the air, and heat the sample over a flame. Note the moisture which collects 

 near the top of the tube because it is the coolest part. Such moisture when 

 found in dry road dust or other dry soil is called hygroscopic moisture. The 

 films on the soil grains are finer than in capillary moisture. 



5. Percolation in Different Soils. Place a sample of clay and a sample of 

 sand packed alike in two lamp chimneys of the same size, and having cloth 

 tied under each to hold the soil. Set them in a dry pan, and pour water in 



