342 ANNUAL REPORT OF THE Off. Doc. 



Froe waLc'j- is thai wiiieli inovi's undci' Ibc? inllueiice of ^ravitA" and 

 is the soui't'o of supply of oiii- woUs and springs. It is not directly 

 useful to plants and its presence too near the surface is injurious 

 to vegetable life. It, however, forms a reserve supply from which 

 capillary water is continually drawn. Capillary water is that which 

 nils the openings between the particles of soil and is the direct 

 source of supply for plants. If a towel be suspended in water the 

 former will gradually become wet a considerable distance above 

 the level of the water. The' water rises in the soil in the same 

 manner and this phenomena is what is termed capillary action. 

 This capillary action does not necessarily take place from deep in 

 the soil toward the surface, but rather from the more moist to 

 the dryer portion of the soil. As a rule, of course, the dryer soil is 

 to be found at the surface. Here is where water is being constantly 

 evaporated and the movement is from underneath upward to supply 

 this loss. In a dry time this force is sufficient to raise the water 

 through several feet of earth. So-called hygroscopic water is that 

 held firmly by the soil and freed only when exposed to a temperature 

 equal to that- of boiling water. As far as its practical bearing is 

 concerned it may be eliminated from the discussion. 



The physical character of the soil fixes in large measure its power 

 to absorb and retain moisture. In general, the finer the soil grains 

 the more water the soil will hold, and when once absorbed the 

 more readily the moisture will respond to the capillary action, and 

 the more tenaciously such a soil will cling to its moisture. Where 

 a clay soil, which is composed of fine particles, under ordinary field 

 conditions contains 34 per cent, of moisture, a sandy soil, under 

 the same conditions, contains only a little over 17^ per cent. On 

 the other hand, the smaller the size of the spaces through which 

 the water must flow passing downward under the influence of grav- 

 ity, the slower will be the rate at which it w il move. That soil, 

 therefore, which will hold the largest volume of water, whose par- 

 ticles are fine clay, is least impervious to water and much loss may 

 occur through surface drainage. In cases of soils -having a loose, 

 open texture, as sandy soils, water percolates readily, and may be 

 lost by passing downward beyond the reach of root action. 



In the conserA'atiou of soil moisture, effort should first be directed 

 toward ameliorating these conditions. The greatest factor in 

 bringing about this improvement is the presence of humus or de- 

 cayed vegetable matter. It is the humus which imparts a sponge- 

 like condition to the soil. In case of heavy clay soils the small par- 

 ticles of which they are composed will be flocculated, thus tending 

 to open up the pores and admit of the more ready penetration of 

 both water and air. On the other hand, it will affect the lv'>ose, open 

 soil by binding the particles more closely together, bringing about 

 in both cases an intermediate condition. 



