PRACTICE XII 



-3*6- 



DETERMINATION OF APPARENT SPECIFIC GRAVITY OF 

 SURFACE SOIL UNDER FIELD CONDITIONS 



Two students may work together, one taking plowed ground, 



the other sod near by. 



Take a tube 1 similar to Fig. 4 

 and force it into the ground to 

 the depth of 6 inches. 



Remove the soil to a weighed 

 pan. Collect another sample of 

 the same soil under identical con- 

 ditions, using every precaution to 

 have the duplicate similar. Dry at 

 room temperature for a day or two 

 before placing in the oven at 100 

 C. to dry for twenty -four hours. 

 Calculate the volume of soil taken 

 and divide the weight of water- 

 free soil by this. The result is the 

 apparent specific gravity. 



The apparent specific gravity of 

 soils in the field may be taken as 

 an approximate indication of their 

 tilth, since the better the tilth the 

 lower the apparent specific gravity 

 for the same kind of soil. This is 

 due to the fact that soils in good 

 tilth are looser on account of the 

 presence of a larger proportion of 

 organic matter and better granu- 

 lation. The apparent specific 

 gravity of a continuously cropped 

 soil is higher than that of one on 

 which proper rotations have been 



, n practiced. Why ? 



if It will be well to collect samples 



under varied conditions and have 



each student secure the results from a number of others and 

 tabulate in his guide for purposes of comparison. 



-8*- 



1 An iron or brass tube 2 or 3 inches in diameter, with a cutting edge. 



26 



