i8 



AGRICULTURE 



Differences between Sand and Clay. What have we learned 

 from these experiments with sand and clay ? We have found that 

 sand is heavier in weight than clay; it is composed of small, hard 

 grains which do not adhere closely; it holds little water, settles 

 quickly in water, and is not sticky. We have learned that clay 

 consists of very small particles which adhere closely; it holds 



much water, does not settle quickly 

 in water, and is sticky. These dif- 

 ferences are largely the result of one 

 thing, a difference in texture. The 

 texture of sand or clay, like that 

 of cloth, depends upon the size of its 

 particles and their relation to one an- 

 other. We say of clay, as* of muslin, 

 that its texture is ' fine ' and ' close,' 

 - that is, its particles are small and 

 near together; we say of sand, as of 

 bagging, that its texture is * coarse ' and ' loose,' that is, its 

 particles are large and far apart. 



Humus. But let us look at the dark-colored substance called 

 humus, which we place in a third gill measure. Humus is not 

 formed, as are sand and clay, *by the breaking down of rocks ; it 

 is formed by the decay of vegetable matter. You observe that 

 humus is light in weight, lighter than clay and much lighter than 

 sand. It is soft to the touch, because its particles are very fine. It 

 absorbs a great deal of water and dries very slowly. Its capacity 

 for absorbing and holding water and heat is a very important quality 

 of humus. Although humus is soft to the touch, it is not sticky 

 like clay, and it does not ' bake,' or dry hard. 



Effect of Humus on Sand and Clay. Now let us divide this 

 humus and add half to the sand and half to the clay. We find that 



SOIL PARTICLES, MAGNIFIED 

 162 TIMES 



