76 ELEMENTS OF AGRICULTURE 



(4) Decaying organic matter. 1 



(5) Living organisms. 



There are very few soils that are capable of producing 

 crops that do not have all these constituents. About the 

 only exception is the class of soils that do not contain 

 rock fragments. Muck contains little such material. Nearly 

 all of its solid matter is made up of organic material. It 

 is one of the most valuable soils for growing celery, 

 onions, and some other crops. 



A soil that is very deficient in water, air, living organ- 

 isms, or decaying organic matter, will not produce good 

 crops. 



ROCK PARTICLES 



74. Amounts of Mineral Matter. The rock particles 

 in most soils make up 65 to 95 per cent of the weight. The 

 organic matter usually constitutes 2 to 5 per cent. Most 

 of the remaining weight is water. The mineral matter 

 furnishes the solid food. It also acts as a reservoir for 

 holding the water. In the study of geography, we have 

 learned how the particles of rock have become so small. 

 The size of the particles has very much to do with the 

 value of the land. 



75. How the Size of Particles is Determined. If a soil 

 is thoroughly shaken up with water and then allowed 

 to settle a few minutes, the larger particles will be sepa- 

 rated out. The rily water can be poured off and allowed 

 to settle for a longer period, when the next larger particles 

 will have settled to the bottom. If the rily water is again 



1 Organic matter is any material that is, or once was, an organism, or 

 living thing, such as coal, wood, sugar, straw, manure, etc. 



