No. 6. DEPARTMENT OP AGRICULTURE. 629 



SOME SOIL PROPERTIES AND THEIR RELATION TO CROP 



PRODUCTION. 



By H. O. SAMPSON, B. 8., B. S. A., Instructor in Agriculture, Waterford, Pa., High School. 



It is the purpose of this article to treat, in a general manner, somy 

 of the very interesting properties of the soil and to show their rela- 

 tion to crop production. In the first place, let us consider of what 

 the soil is composed, and then inquire into the agencies which are 

 instrumental in its formation. 



If a handful of earth be examined microscopically, it is found to 

 consist of small grains of sand (rock material) and bits of decayed 

 vegetable matter, sometimes in such a state of decomposition that 

 the original form is lost, while in other cases the form is still intact. 

 At other times our handful of earth may not show any distinct 

 sand grains, but is a black, finely pulverent mass known in most 

 cases as humus. If, however, a small portion of it be placed between 

 the teeth, we are soon convinced of its gritty nature. 



The microscope tells us more of the soil's true composition; even 

 with a simple lens, it is seen to be made up of pieces of grit or sand 

 of varying sizes, mixed with organic matter. The compound micro 

 scope shows these sand grains to be fragments of quartz, bits of 

 feldspar, shreds of mica, or some other mineral substance. Often, 

 however, these minerals are in such an advanced state of decomposi 

 tion that their distinct mineral character are lost. 



Granting that the soil is a mixture of various mineral particles 

 and organic matter, let us consider the causes of its formation. In 

 nature nothing is at rest. Agencies are everywhere active, tearing 

 down and building up, changing materials from one form to another. 

 These changes are of two kinds, chemical and physical. The forces 

 may act singly or together, but in all this process of change, noth- 

 ing is lost. The conservation of matter is complete. 



Finding our soil made up of mineral particles, we naturally look 

 to the rocks as the source of these materials. That the solid rocks 

 are broken up by Nature's agents may readily be observed. The 

 rending action of frost on a quarry face is a familiar example. These 

 agents of disintegration will be considered later. A rock, as we 

 know it, is made up of an aggregate of minerals. A mineral is a 

 substance in nature having a definite chemical compound. That a 

 rock is composed of minerals may readily be seen by examining a 

 hard specimen of granite. With the naked eye one is enabled to 

 distinguish particles of the minerals, quartz, feldspar, mica, and 

 sometimes, hornblende. If a thin section of this same granite be 

 examined under a microscope, the mineral character is more pro- 

 nounced. In addition to the minerals named above, we may find 

 small crystals of apatite, etc., or other such minerals. Therefore, 

 since the soil particles examined were made up of similar minerals, 

 we naturally conclude that they were derived from the rocks. The 

 process of soil formation may be considered under the head of rock 

 weathering. Many and varied are the agents which contribute their 

 share to the process. The action of the forces at work may cause 



