8 BULLETIN 521, U. S. DEPARTMENT OP AGRICULTURE. 



and other plants were noted? Did you note any particular effects 

 of the work of animals ? To what agents do you attribute whatever 

 crumbling of surface rocks you have seen ? Why should the farmer 

 understand the forces and agents which are making and moving soils ? 

 Can the farmer do anything to aid the formation of soils? Can he 

 do anything to hold the soil where it is needed ? 



Lesson 4. — Physical Nature of Soils. 



1. Fineness of soils. 



2. Texture of soils. 



3. Weight of soils. 



4. Color of soils. 



Lesson 5. — Water-holding Capacity of Soils. 



1. The soil as a reservoir for water. 



2. Forms of soil moisture. 



3. Relation of capacity to nature of soil. 



4. Relation to depth of soil. 



Exercise 5. — A Study of the Water-holding Capacity of Soils. 



Purpose: To test the capacity of soils of different types to take 

 in rainfall or irrigation water. 



Directions: Tie cheesecloth over the small ends of five student- 

 lamp chimneys, which should then be mounted in a rack with the 

 covered ends each placed in a glass tumbler. (If the lamp chimneys 

 can not be procured, long-necked bottles, such as vinegar bottles, may 

 be used after the bottoms have been removed in the following manner : 

 File a groove parallel with the bottom. Lay a poker heated red hot 

 upon the groove. As soon as a small crack* is started draw the poker 

 around the bottle and the crack will follow.) Fill the chimneys or 

 bottles to the same height with the following kinds of soil : (1) Gravel, 

 (2) sand, (3) loam, (4) clay, and (5) peat or leaf mold. The soil 

 should be made firm by jarring the rack three or four times. Pour 

 water into each of the chimneys just rapidly enough to keep the sur- 

 face of the soil covered and note the exact time before it begins to 

 drop into the tumbler below. 



To show the effects of packing take two chimneys with an equal 

 quantity of the same kind of soil, packing it firm in one chimney 

 and leaving it loose in the other. Repeat the water-pouring process, 

 noting the time as before. 



To show which soil drains the more readily empty and replace each 

 tumbler as soon as all free water has disappeared from the upper 

 surface of the soil above it. After the water has ceased dripping 

 from all the chimneys measure and compare the water in each tumbler, 

 making a record of the order in which they cease dripping. 



To determine which soil will store up the greatest quantity of 

 moisture weigh each chimney before and after filling it with dry 

 soil, and again after the water has ceased dripping from it. The 



