96 A YEAR IN AGRICULTURE 



that the fanner can do to prevent the wearing out of the 

 soil: first, he can so treat the soil as to assist and hasten 

 nature in the process of making plant-food; second, he can 

 return to the soil an amount of plant-food equivalent to that 

 removed by the crop. 



Classification according to texture and structure. When 

 the soil is formed by so many varied agencies as are enu- 

 merated above, it is clear that it will vary in fineness of 

 texture according to the degree to which the rock material 

 has been reduced. Some particles are so small that twenty- 

 five thousand of them can be placed in a linear inch. It is 

 impossible for the unaided eye to distinguish such small 

 objects. From this extremely small size the particles range 

 in size to small stones. Some soils are composed almost 

 entirely of the smallest particles, while others are made up 

 of coarser material. The size of the unit particle determines 

 soil texture; the arrangement of these units determines soil 

 structure. The fineness and arrangement of the rock parti- 

 cles, together with the kind of rock from which the soil was 

 derived, influence greatly the producing power of the soils. 



Soils may be classified, based upon size of the particles, 

 into stony soil, gravelly soil, sand, silt, clay, and loams. The 

 various grades of soil particles and amounts present, together 

 with the amount of organic matter, give rise to the names 

 of the common soil types; as, black clay loam, brown silt 

 loam, gray silt loam, yellow silt loam, peat, peaty loam, 

 sandy loam, etc. Reduction in size of particles in- 

 creases the internal area or total area of all particles, 

 thereby increasing the feeding area for the root hairs and 



