166 



ANNUAL REPORT OF THE 



Oft. i)oc. 



It will, of course, be understood that the soil grains take no such 

 orderly arrangement, one resting above another, or one between two 

 other, as do marbles packed in open or close form. Their great 

 variation in shape, weight and size; their extreme lightness, and their 

 tendency to adhere to one another when moist, precludes order in 

 their arrangement. But in all soils having a greater diameter than 

 clay or fine silt, the object most to be desired is a uniform arrange- 

 ment of the soil particles, thus securing the highest number of con- 

 tacts between them, giving the conditions most favorable to obtain 

 a high-water content. 



WATER IN THE SOIL. 



When the rain falls more rapidly than drainage, either natural or 

 artificial, can remove it, and the water fills all the spaces between 

 the soil grains, it is called "gravitation water," and in this condition 

 the soil is fully saturated. While this condition exists, the water 

 moves in one direction only, downward, acting under one force, 

 gravity. The rate of flow is fast or slow, just as the soil particles 

 are coarse or fine, and the spaces between great or small. In other 

 words, friction and outlet below control the speed. When a cubic 

 foot of average soil having 50 per cent, of air space is fully sat- 

 urated, it contains half a cubic foot of water, or 31.25 pounds, of 

 3.75 gallons, or 50 per cent, by volume. Gravity will remove half 

 of this quantity of water. Capillary attraction, or surface tension, 

 as it is better called, will hold back one-half, which is spread in a 

 thin film over the exposed surfaces of the soil grains. When the 

 water carried down by gravity descends beyond the reach of plant 

 roots or escapes in drain tiles, it has passed beyond the control of 

 the farmer, but the water held back by surface tension is largely 

 within his control, and the quantity he will utilize is measured by 

 the means used to prevent its escape except through the leaves of 

 the growing crop. 



Figure 3 with proportion of soil 



grain to water film exaggerated, 



shows how the water films sur- 

 round the soil grains and thicken 



at the points of contact. This 



naturally suggests that the more 



the compacted soil is pulverized 



and the particles separated so 



that they will rest loosely and 



together with many 



contact around which 



films may thicken, 



then the more water such a well 



cultivated soil will hold back from 



drainage. 



uniformly 

 points of 

 the water 



Fig. 



CAPILLARY RISE. 



A glass tube one-tenth inch in diameter will lift a certain weight 

 of water over one-half an inch (5.45) above the level of the water in 

 which the end of the tube rests. A tube one-hundredth of an inch 

 in diameter will lift the same weight of water nearly five and a half 



