26 



SOIL COMPOSITION, CLASSES AND TYPES 



Demonstrations. — Materials Needed, — Four large, clear-glass bottles; a 

 small amount of clean sand, silt, some clay, and two or more tablespoonfuls 

 of loam. 



To Show the Comparative Rate of Settling of Sand, Silt and Clay Particles 

 Out of Water. — Procedure.—'E&-ve prepared 4 large, clear-glass bottles and fill 

 each about three-quarters full of water. Place in one some sand, in another 

 some silt, in the third some clay, and in the fourth a tablespoonful or more 

 of loam. Cork. Shake each thoroughly, invert, and note the rate of settHng 

 of the soil particles. 



Questions, — (a) Why should the banks of a stream which overflows often 

 be higher than the land farther back? 



(6) A river flows southward. In the middle of the stream is a sand island 

 which becomes covered at high water. On which end (north or south) of the 

 island wiU the fine sand be found? Why? 



(c) During a heavy rainstorm a gully was formed on a sloping field of 

 heavy silt loam soil. Below the mouth of the guUy on the field below consider- 

 able sand was deposited. Where did the sand come from? 



Laboratory Exercises. — Matenals Needed. — ^A hand lens; a high power 

 microscope if avaOable; a dozen tumblers or other dishes; a small baking 

 powder can; 2 to 4 quarts of each of the eight important soil classes, also muck 

 and peat; a balance; soil maps; state map showing township and range. 



To Examine the Building Material of Soils. — Procedure. — With the aid of 

 a hand lens examiae a pinch of sand and a pinch of loam. Distinguish between 

 sand, silt and clay particles. (Set up a high power microscope if convenient.) 



Questions. — ^What are sand particles? Silt? Clay particles? 



To Study Soil Structures. — (Arrangement of soil particles.) Procedure. — 

 With the aid of a hand lens examine the structure of a mass of clay. Of sand. 

 Of crummy silt loam. Illustrate observations with drawings. 



Questions. — (a) Of what materials are soil crumbs composed? 



(b) What binds the soil particles into cnunbs or granules? 



To Study Texture of Soils. — Procedure. — ^Place in tiunblers or in other 

 convenient dishes, dry and tj^pical samples of the eight important classes of 

 soil (based on texture). Vary the color as much as possible, and have duph- 

 cates of some of the classes. Provide a moist sample of each. Include muck 

 and peat in this exercise- Record results as follows: 



SoO classes named in 



order according to 



texture 



How distinguished * 



Per cent 

 sand 



Per cent 

 silt 



Per cent 

 clay 



Characteristics 



Note "feel," whether 



gritty, velvety or sticky 



* Teacher should supply percentage ranges of sand, silt and clay. 



Questions. — (a) Explain this statement — "A sand is not necessarily 

 all sand. "^ 



(h) Give meaning of "A clay must contain at least 30 per cent clay." 



(c) What is a loam? 



(d) What is a loamy soil? 



(e) What makes a soil loamy? 



(f) What is a heavy silt loam? 



