LIFE IN THE SOIL 97 



LIFE IN THE SOIL 



105. Importance of Soil Organisms. As we have seen, 

 soil is not a dead thing. It is much more than a collection 

 of rock particles. It is teeming with life. Without this 

 life the soil would never have been able to produce farm 

 crops. If all the living things in the soil should die, the 

 soil would soon fail to produce crops. Keeping the soil 

 productive is very largely a matter of keeping these 

 organisms thrifty. The roots and stems of plants furnish 

 food for the bacteria and molds. The waste products 

 furnish food for other bacteria. Eventually, the food is 

 in a form available for crops to use again. So the material 

 is worked over and over again. Any break in the link 

 will affect all of the chain. If the organisms do not decom- 

 pose the roots and stems properly, the new crops will 

 suffer. If there is not enough humus in the soil, the bac- 

 teria suffer and crops are immediately affected. 



Earthworms serve a useful purpose in the soil by help- 

 ing to break down the organic matter. They also do much 

 good by making the soil porous. A soil that is full of earth- 

 worms is nearly always fertile. 



The molds help in breaking down the organic matter, 

 particularly the woody matter; but the most important 

 forms of life in the soil are the microscopic organisms, 

 yeasts and bacteria. 



106. Soil-Bacteria are very minute living things, far too 

 small to be seen with the naked eye. They are so small that 

 they have to be magnified 500 to 1 ,000 times before they 

 can be seen with a microscope. (See Fig. 48.) On an average, 

 it takes about 25,000 bacteria placed end to end to meas- 



