CHAPTER IV 



TEE SOIL PARTICLE AND CERTAIN IMPORTANT 



RELATIONS 



An examination of a soil, however cursory, immediately 

 reveals that it is made up of irregular fragments of mineral 

 material mixed and more or less coated with organic matter. 

 These fragments, varying in size from particles easily discern- 

 ible by the naked eye to particles so fine as to be invisible 

 tinder the nltra-microseope, determine to a very large degree 

 the complex relationships of soil to plant. The movement of 

 air in the soil, the circulation of the water, chemical reactions 

 resulting in solution, and the presence and virility of the 

 various organisms are determined largely by the size of par- 

 ticles making up a soil and by the proportion and condition 

 of the organic material present. In expressing the size or 

 sizes of particles making up a soil, the term texture is used. 

 Thus a soil texture may be coarse, medium, or fine, indicating 

 that the particles making up the soil conform in general to 

 such description. 



Texture is a condition which can be but little modified in 

 a normal soil. We have seen how a rock can be disintegrated, 

 decomposed and gradually built into a soil. A change in 

 texture has been wrought, but such a process demands geo- 

 logic ages for its fulfillment. In the time covered by the life 

 of man, the necessary forces are not active enough to have 

 this effect; consequently, as far as the farmer is concerned, 

 the texture of the soil in his field is subject to but slight 

 alteration. A sand remains a sand and a clay remains a clay, 



as far as practical considerations are concerned. Changes 



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