22 BULLETIN 355, U. S. DEPAETMENT OF AGRICULTURE. 
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 farm 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 HI. 
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 1-inch 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? 
