NATURE OF SOIL 



307 



From this table it is seen that Norfolk sand, which is 

 an excellent soil for truck gardening on the Atlantic, is 

 eighty-eight per cent, sand and gravel, and only twelve per 

 cent, silt and clay combined. Middle western silt loam, 

 such as grows most of our field corn, is three-fourths silt, 

 and fifteen per cent, clay and twelve per cent. sand. River- 

 bottom clay soils are slightly more than one-third clay, and 

 almost one-half silt. 



4. Structure of Soils 



Take a piece of clay in your hand. Try to crumble it 

 into small particles. Do the same with a piece of loam; 

 with a lump of sandy soil. Note that some soils plow up 

 in great clods, while others break up into small pieces, pro- 

 ducing what is called a mellow condition. Have you no- 

 ticed that in some places the ground cakes and cracks open 

 when it becomes very dry, while in other places it remains 

 soft and unbroken no matter how dry it becomes? These 

 differences are matters of soil structure. 



Soil structure. By soil structure is meant the mode 

 in which particles adhere to one another, causing them to 

 cling together in solid masses hard to break up, or forming 

 but loosely joined lumps easily broken or pulverized. 



Clay soils are of a heavy, dense, clinging structure, dif- 

 ficult to break apart, hence hard to plow. Silt loams 

 and sand loams, on the other hand, are friable; that is, 

 they are easily broken up. They plow or pulverize easily 



