474 introduction to the Study of Science 



Find experimentally the capacity of a fine clay loam for moisture, 

 for air, and for heat ; of a coarse sandy loam for each of these. Com- 

 pare the two. Why is one better in all these respects than the other? 

 In which is the rate of evaporation higher? Which in normal cir- 

 cumstances will have the better soil temperature for germinating seeds ? 



Suppose in preparing a soil for a house plant, you find its tempera- 

 ture is too low for the best growth of the plant. How can you correct 

 it? How can you correct it if you find the soil too warm? How can 

 you keep the nroisture and temperature of a soil fairly stable ? What 

 is the effect of a closely packed surface upon moisture and tempera- 

 ture? What is the effect of a fine mulch surface? Give instances 

 where it is important to know how to regulate the moisture and tem- 

 perature of a soil. 



SUMMARY 



The human race is dependent for food mainly on the soil and its 

 productivity. 



Humus is decaying vegetable matter 'in soil. Accumulations of 

 humus in swamps are called muck or peat. 



Soils may be classified on the basis of the size of the rock particles 

 they contain, as clay, silt, sand, and gravel. Soils containing an 

 abundance of humus are called loams. 



Soils are often named from their origin, as alluvial, glacial, or 

 lacustrine. 



On the basis of water content soils are classified as humid or arid. 



The amount of soil water that any soil will hold depends mainly 

 on the size of the rock particles and the amount of humus contained. 



Water held by capillary action in the soil is called soil water. It 

 contains something of all substances with which it comes into contact 

 and so supplies the plants with many indispensable elements. 



Soil water enters plants through the walls of the root hairs by 

 osmosis, due to a difference in density of the sap and the soil water. 



Water escapes from leaves by evaporation and passes as a vapor 

 through the leaf pores. The process is called transpiration. 



Commercial crops need different amounts of water to bring them 

 to maturity. 



A large percentage of the weight of plants and their products is 

 due to water. 



Dry farming is practiced in many localities where the annual rain- 

 fall is insufficient to mature an ordinary crop. It consists in packing 

 the subsoil to insure its capillary action, and stirring the surface soil 

 to decrease its capillary action and prevent evaporation. 



