EXERCISE 15 



THE TILTH OF SOILS 



Statement. The presence of organic matter in the soil has the property of causing the soil grains 

 to cling together in aggregates, making the soil mellow and crumbly. Therefore, a soil rich in organic 



matter is usually a soil of fine tilth. The presence of organic mat- 

 ter in sandy soil increases its water-holding power without de- 

 stroying its open or porous structure. The presence of lime 

 makes the soil mellow by causing soil aggregates to form. 



Object. To show the effect of the presence of organic matter 

 and lime upon the structure and tilth of soils. 



Materials. Clay soil ; dry, finely pulverized barnyard ma- 

 nure ; three shallow pans ; three flowerpots or tin cans ; seeds of 

 corn or beans; two eight-inch test tubes or slender bottles, as 

 olive or pickle bottles; tablespoon; teaspoon; one-half pint of 

 air-slaked lime. 



Directions, i. Stir a pan of clay and water until a smooth 

 batter is formed. Pour each of the three shallow pans almost full 

 of this batter. To one add 

 one-fourth pint of pulverized 

 barnyard manure and stir it 

 into the batter. To the second 

 pan add a tablespoonful of 

 lime and stir it into the bat- 

 ter. Leave the third pan of 



batter untreated. Set them all aside, and when they are dry, 



compare the ease with which they crumble. Compare the crumb 



structure under the microscope. 



2. Fill three flowerpots each three-fourths full of clay. Fill 

 one of them the remainder of the way with pulverized manure. 

 Pour out the clay and manure, thoroughly mix and replace 

 them in the pot. To the clay in another pot add .two table- 

 spoonfuls of lime and stir well into the soil. Leave the other 

 pot untreated. Plant seeds of corn or beans in each pot, and 

 water as necessary. Compare the rapidity of growth. Explain 

 the difference. 



3. Place one-half teaspoonful of finely pulverized clay soil in 

 each of the two test tubes, and to one add one-fourth teaspoon- 

 ful of powdered, air-slaked lime. Fill both with water and 

 stir vigorously. Set them aside and note which clears first, 

 ence in the rate at which the soil settles in the two tubes, 

 and why? 



Questions. Which pot of soil is the best aerated? Why? How does organic matter affect soil 

 structure ? How did lime influence the structure of the soil particles ? 



References. Waters, H. J. Essentials of Agriculture, p. no. Ginn and Company. 

 Soils, pp. 103-108. Orange Judd Company. Lyon, Fippin, Buckman. 

 ment, pp. 150-160, 190-193, 218. The Macmillan Company. 



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Fig. 19. A soil of excellent tilth 



FIG. 20. A soil which lacks tilth 



Explain the reason for the differ- 

 Which soil has the better tilth, 



Burkett, C. W. 

 Soils, their Properties and Manage- 



