THE CULTURE OF FARM CROPS. 



CHAPTER XX. 

 ^ THE PHYSICAL PROPERTIES OF SOILS. 



While the later and more accurate knowledge regarding 

 the relation of soils to the growth of crops, has rendered 

 obsolete many of the former views and opinions held by 

 agricultural students in respect of the importance of this re- 

 lation, yet the practical farmer will easily recognize the 

 fact that the physical conditions of the soil ; that is, its den- 

 sity ; the fineness of its particles ; its firmness and adhesive 

 power; its capacity for imbibing and retaining moisture; 

 its color ; the amount of contraction upon drying ; its po- 

 rosity and consequent power of admitting air, and gaseous 

 substances with it : that all these are of primary importance 

 to its successful culture and worthy of careful consideration 

 and study. 



Some soils are much heavier than others ; not only in 

 reference to the ordinary sense in which the terms "heavy" and 

 "light" are used to denote clay or sandy soils; but as re- 

 gards the absolute specific gravity and the weight of equal 

 bulks. Thus a cubic foot of 



Dry sandy or limestone soil weighs 110 Ibs. 



Clay loam, half sand 95 



Heavy sandy loam 80 to 90 



Pure clay 75 



Rich garden mold 70 



Peaty soil from swamps 30 to 50 



Sandy soil, largely made up of quartz is the heaviest and 

 the weight of soil is less as the proportion of clay and veg- 

 etable matter increases. This quality of the soil is not 

 without practical importance: for the heavier a soil is the 

 less it is compressed or packed by the passage of loads or of 

 cattle over it ; the less it is washed by heavy rains ; and ac- 

 cording to a number of experiments made in Germany it 

 has been shown that the denser and heavier the soils, the 



