126 POMOLOGY 



Silt 1/500 to 1/2000 of an inch in diameter. 



Fine silt 1/2000 to 1/5000 " " '' " 



Clay 1/5000 to 1/250,000 '' " " " 



Sand is a valuable component of an orchard soil, although 

 in itself it does not contain plant-food, since the sand par- 

 ticles are largely quartz which weathers very slowly. It 

 is of value because it lightens the soil, gives it natural drainage 

 and has a tendency to make it warm. 



Clay is composed of very small particles, microscopic in 

 size, and forms to a considerable extent the body of the soil. 

 It is derived from various rocks and carries considerable 

 of the mineral elements of plant-food. The colloids of the 

 soil, which have recently received considerable attention, 

 are associated with the finer clay particles. If clay is present 

 in abundance, the soil will diy badly, shrink, and crack 

 during very dry periods. On the other hand, clay causes 

 the soil to be heavy and difficult to work when wet. 



Silt is much the same as clay in its character but the 

 particles are intermediate in size between the sands and 

 clay. A soil containing large amounts of silt is usually 

 moderately rich, well adapted to the growing of the grain 

 crops. 



Humus is a term given to decomposed vegetation and is 

 of signal value in increasing the water-holding capacity of 

 a soil and in causing it to be mellow and easy to work. This 

 term is often used loosely or incorrectly, since vegetation 

 plowed into the soil does not become humus until it is 

 thoroughly decayed. The humic acids produced during 

 decay contribute materially to the setting free of plant- 

 food m'aterials in the soil. 



The term loam is used to describe a soil made up of a 

 combination of sand, silt, and clay and it is further defined 

 by the predominance of one or the other, as sandy loam, 

 silt loam, or clay loam. The fruit-grower is interested in 



