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The Cornell Reading-Courses 



Pore space 



Much has been said about pore space in the soil. A soil is made up 

 of several materials. Chief of these are the soil particles, water, and air. 

 A fertile soil for the staple upland crops must have a proper proportion 

 of each of these constituents. If there is too much soil there may be a 

 deficiency of water or air or both, according to the division of this space. 

 If there is too little soil the proportion of pore space is excessive. If the 

 spaces are large, as they are likely to be, they permit leaching and retain 

 insufficient water for the needs of plants; and the excessive ventilation 



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Fig. 90. — An illtistration of soil in bad tilth, and of poor plowing. The soil is heavy 

 clay and was much too wet to be plowed effectively. The shining surface at the bottom 

 of the furrow slice indicates the presence of too much water. Several seasons of careful 

 tillage will be required to overcome the bad effect of such practice 



and the high temperature that result, cause a wasteful decay of organic 

 matter. While heavy clay, on the other hand, may have a larger total 

 volume of pore space, it has the space much more subdivided so that it is 

 effective in absorbing and holding water. When puddled, the pores 

 become so small and the water is held so tenaciously that it is of little 

 service to plants. 



The importance of the right proportions of these three constituents and 

 of their relation to texture and structure of soil is well shown in the 



