22 BULLETIif 355, U. S. DEPAETMENT OF AGEICULTUEE. 



TILTH. 



(Ref. No. 2, pp. 277-283.) 



Soil management to produce good tilth. — Ample pore space and 

 thorough granulation in a soil are two of the most important factors 

 of good tilth. It is impossible in a brief treatise of this kind to for- 

 mulate rules for tillage covering the use of all farm implements, 

 for all farm crops, grown upon all types of soil. But a thorough 

 knowledge of the principles involved and the ends to be attained 

 is of greater value in fann practice than any set of rules. It is only 

 by experience, together with a mastery of the principles of soil man- 

 agement, that the best tilth will be secured and the best results in 

 farming produced. This is especially true of the different clay 

 soils, many of which are fertile, but all of which require intelligent 

 management. 



EXERCISES, LESSON in. 



Materials needed. — One-pound baking-powder cans; a balance or scales, 2 quarts 

 each of dry sand, clay, silt loam, clay loam, sandy loam, loam; several l-incb wooden 

 cubes; any simple apparatus to measure cubic inches of water; set of soil sieves; pie 

 tins, or saucers. 



SOIL TEXTURE. 



Heavy versus light soils. — Take two 1-pound baking-powder cans of equal weight 

 and fill one level full with air-dried sand. Fill the other with finely divided air-dried 

 clay or silt loam. Compare the weights of these two volumes of soil. Which does 

 the farmer usually consider as light soil? Why? Why is the other commonly called 

 a heavy soil? To which soil may the term fine textured be applied? Describe the 

 texture of the light soil. 



Soil classes based on size of soil grain (Ref. No. 3, p. 77). — Obtain dry samples of 

 sand, clay, silt loam, sandy loam, clay loam, and loam. Examine each class care- 

 fully with a hand lens and note the following characteristics: Comparative size of 

 soil particles; the feeling between the fingers when wet, whether gritty, sticky, or 

 velvety; kind of soil particles based on texture. 



(To THE LEADER. — A tablespoonful of each sample of soil may be placed in separate 

 small dishes and labeled to enable the members of the class to work alone or in pairs. 

 After the members have become familiar with each soil class, unknowns may be 

 passed out for identification.) 



Mechanical analysis. — Take about half of a pound baking-powder can of two or three 

 different kinds of dry soil. Weigh each sample separately and record. Take one 

 kind of soil and pour upon the coarsest soil sieve. Shake until no more of the mate- 

 rial passes the sieve. Retain the part passing through. Weigh the part retained by 

 the sieve and record the weight. Take the part passing through the sieve, repeating 

 the process as above with the next finer sieves in order and recording the weights, 

 until all the sieves have been used. Compare percentage of separates with table on 

 page 18, and try to determine the correct names for classes of soils used. 



Texture and film water (Ref. No. 2, pp. 157, 158). — (a) Take eight 1-inch cubes and 

 build them up into a 2-inch cube. How many square inches of surface does this 

 2-inch cube have? Determine the total number of square inches of surface on all 

 the smaller cubes. 



Cutting a cube in three directions increases the number of cubes how many times? 

 How many times does it increase the surface area? 



