THE SOIL 



its growing season. Some it gets from the air, but for the greater 

 portion it depends upon its storehouse, the soil. 



Soil Water. If you dig down into the soil, you find it moist 

 below the dry surface, even when there has not been rain for sev- 

 eral days. Each particle of this moist soil is surrounded by a 

 film of water. Around these particles is air. The finer the 

 particles of soil, the more numerous are the water films and 

 the air spaces. Fine-grained clay can contain three or four 

 times as much water and air as can coarse-grained sand. 

 Careful experiments prove that under average weather condi- 

 tions there is in twelve inches of well-tilled loam about four 

 thousand barrels of water to the acre. Near or far below the 

 surface, a depth is reached where the soil spaces are filled with 

 water instead of air. This is called the ' water table.' 



The water in the soil is always in motion. 

 Sometimes it is drawn downward by the force 

 of grav'i ty. Sometimes it is drawn upward by 

 the force of cap'il lar'i ty. 



Gravity. Gravity is the tendency of particles 

 or bodies toward a center of attraction. It is 

 this force which makes the apple fall and 

 which makes the rain sink into the wet earth. 

 Coarse, sandy soils offer little resistance to grav- 

 ity and allow water to sink freely, but fine clay 

 soils hinder its action. If this force worked 

 alone, all water would sink into the earth out capillary water held 

 of reach of plant roots. 



Capillarity. The force of gravity is counter- 

 acted by the force of capillarity, or cap'il la ry 

 attraction. Capillarity causes a fluid to ascend through a porous 

 substance ; it makes oil rise in the lamp wick, ink in the blotter, 



between two 

 grains, greatly 



soil 

 en- 



