26 SOILS 



THE WEIGHT OF SOILS 



This depends upon their composition and com- 

 pactness. It is of interest to the farmer chiefly as 

 an indication of the amount of vegetable matter 

 that a soil contains, because this influences its value 

 for cropping. The coarser the grains, the heavier 

 the sou; humus makes a soil lighter. A heavy 

 soil one weighing over 80 Ibs. per cubic foot is 

 likely to be benefited by the addition of humus. 

 As the term is commonly used, however, a heavy 

 soil is one that is tenacious, and refers to texture, 

 not to weight. 



Schubler gives the average weight of a cubic 

 foot of dry soil as follows : 



Sand 100 Ibs. 



Garden Soil rich in humus 70 Ibs. 



Peat Soil 30 50 Ibs. 



The weight of the soil on an acre of land is so 

 great 'that if a very small percentage of it is plant 

 food this may amount to a very large quantity per 

 acre. An acre of clay loam, nine inches deep, 

 weighs about 3,000,000 to 3,500,000 Ibs. Suppose 

 this soil contains only one-tenth of one per cent, of 

 nitrogen, which is an average amount of that plant 

 food; the acre would contain, in the first nine 

 inches only, 3,000 to 3,500 Ibs. of nitrogen. Com- 

 pared with this amount, the 30 to 75 Ibs. of 

 nitrogen that we apply as a fertiliser to an acre of 

 impoverished land is a mere bagatelle. 



THE MINERAL CONTENTS OF THE SOIL 



The basis of most farm soils is rock that has been 

 ground into very fine particles by frost, air, water. 



