WATER IN SOIL 



139 



Practical Exercise 1. Read some good reference book and report on how 

 soil is formed. 



You are all familiar with the difference between so-called rich 

 soil and poor soil. The dark soil contains more dead plant and 

 animal matter, which forms the portion called humus. 



Humus contains organic matter. It is easy to prove that 

 black soil contains organic matter, for if equal weights of carefully 

 dried humus and of soil from a sandy road are heated red-hot for 

 some time and then reweighed, the humus will be found to have 

 lost considerably in weight, and the sandy soil to have lost very 

 little. The material left after heating is inorganic material, 

 the organic matter having been burned out. 



Demonstration 1. To find out if all kinds of soil hold the same 

 amounts of water. 



Fill funnels of equal size with equal volumes of gravel, sand, barren 

 soil, rich loam, leaf mold, and pulverized leaves — all dry — then 

 pour equal amounts of water on them and measure all that runs 

 through. Which soil holds the most water? 



Soil water a solution of mineral salts. Water, as it passes 

 through the soil, gradually dissolves very minute portions of the 

 chemical compounds of which the soil is composed, so that soil 

 water is really a dilute solution of mineral salts. 



A plant needs mineral matter to make living matter. Living 

 matter (protoplasm), besides containing the chemical elements 

 carbon, hydrogen, oxygen, and nitrogen, contains very minute 

 proportions of other elements which make up the basis of certain 



