SCIENTIFIC AGRICULTURE. 173 



contain, before it is saturated or full, so as to allow the water 

 to drop or run out 



From 106 Ibs. of dry soil, the water will begin to drop, if it 

 be a quartz sand, when it has absorbed 25 Ibs. 



Calcareous sand, " " " " 29 



Loamy soil, " " " 40 



English chalk, " 45 



Clay loam, " 50 



Pure clay, " " 70 



Power of retaining water. Evaporation is constantly going 

 on from the surface of the earth, except when the atmosphere 

 is saturated, or rain or dew is falling. The rapidity with which 

 soils become dry after rains, depends upon the tenacity with 

 which chey retain water : as a general rule, those soils which 

 are capable of containing the most water, also retain it with 

 the greatest tenacity. Thus a sand soil will lose as much 

 water in one hour as a clay in three, or peat soil in four hours. 

 On this property depends in a great degree the warmth or 

 coldness of a soil. 



The capillary power of the soil is exhibited by pouring 

 water into the bottom of a flower pot, when it will be seen 

 that the earth gradually takes up the water, and the moisture 

 soon appears on the surface. In the same way the surface 

 soil absorbs moisture from the subsoil ; and when this contains 

 an excess of water, the surface is also too wet and cold. Open, 

 porous soils, -such as sand, peat and humus, possess greater 

 capillary power than stiff clay. Upon this action the soil is 

 dependent for its supply of moisture during dry weather: 

 upon this, also, the roots of plants are dependent for a supply 

 of soluble saline matters, which, during rains, have been 

 washed down into the subsoil beyond their reach. This is the 

 principal means by which, in hot, dry climates, where rains 

 seldom or never fall, the soil obtains sufficient moisture to 

 produce vegetation. This capillary action explains the exis- 



*15 



