123 



Physics of the Soil. 



Shubler gives the weight of a cubic foot of dry soil as 

 follows: 



Dry calareous or siliceous sand 110 Ibs. 



Half sand and half clay 96 Ibs. 



Common arable soil 80 to 90 Iba. 



Heavy clay 75 Ibs. 



Garden mould rich in vegetable realtor 70 Ibs. 



Tcut soil 30 to 50 Ibg. 



As a number easy to remember it may be taken as a 

 safe figure that the mean weight of the surface four feet 

 of field soils is, in round numbers, 4,000,000 Ibs. per acre- 

 foot. 



150. Heavy and Light Soils. These terms are used moro 

 with reference to the ease with which soils may be worked 

 than to their weight per cubic foot. A soil that is nat- 

 urally mellow and easily stirred is called a light soil, 

 while one that becomes hard when dry and which tends to 

 form clods is often called heavy.. Sandy soils, as shown in 

 (149) are among the heaviest we have while the clayey va-- 

 rieties are the lightest by weight except. the humus types. 

 The prairie loams which contain much humus and the 

 black swamp soils when drained are among the most mellow 

 of all soils, the large amount of humus preventing the soil 

 grains from adhering and baking. 



