180 THE PRINCIPLES OF SOIL MANAGEMENT 



texture. Up to a height of three feet, the sandy loam 

 moves water most quickly. But when it is necessary 

 to move water to a greater height, a finer soil is required. 

 The maximum height traversed by capillary water 

 in the above soils is fifty-six inches in the silt loam, 

 and in two instances this appeared to be near the 

 limit of capillary efficiency in dry soil of that texture. 

 In clay the movement goes on very slowly, and an 

 excessively long period is required for the limit to be 

 reached. A crop might perish of drought before water 

 would move up to meet its needs. That is, in fine-tex- 

 tured soil, although its capillary capacity is very great, 

 the surface area of the particles is so large, and therefore 

 the friction in the movement of water so great, that the 

 actual capillary movement is very inefficient. 



The same fact appears here that appeared in the 

 discussion of the water capacity of soils, namely, that 

 it is the soil of intermediate texture the silt and fine 

 sandy loam which most readily meets the needs of 

 crops for water. 



85. Dampness of soil particles. The capillary move- 

 ment in dry soil, as given above, does not represent 

 the true capillary capacity. When a soil is dry, it has 

 been shown that it resists wetting, and therefore resists 

 the capillary rise of water. Natural field soils always 

 contain some oily substances, which are deposited on 

 the surface of the soil particles when the soil is dried. 

 This oily matter retards greatly the wetting of the par- 

 ticles, which takes place only after this material has 

 been again dissolved, so that a clean surface is exposed 

 to the solution. Therefore, in a soil which already con- 



