458 ANNUAL. REPORT OF THK Off. Doc. 



The Conservation of Moisture. 



While the chemical and physical character of soils are of primary 

 importance, and do in a large degree determine the possible pro- 

 ductive power of soils, still the handling of the soil possessing these 

 characteristics even in a high degree is of equal importance. That 

 is, a soil however perfect as a place for the growth of plants, or 

 however rich in the plant-food elements, cannot be productive 

 without water, and the amount of water that plants may have at 

 their disposal during periods of limited rainfall is measured in 

 large degree by the methods of practice used. This point is of so 

 much importance and has so intimate a bearing on soil improvement 

 that it warrants a rather detailed discussion of the question of the 

 conservation of soil moisture. 



Water is one of the most important constituents of plants. If 

 perfect growth and development are to be attained, it is necessary 

 that the plant shall be able to obtain a full supply during its entire 

 period of growth. It is not simply a question of water, however, 

 for the water that plants use must exist in a special form in the 

 soil, and it must exist there in proper amounts. Soils may contain 

 too much or be too wet for the proper growth of the most useful 

 plants, if the water is not located in the right place. Water exists 

 in soils in three forms; first, free, or running water, or bottom water, 

 or that which fills the soil, and rises and falls as it is increased or 

 decreased by more or less percolating into it from the rains — the 

 point to which it rises is called the water level; second, capillary 

 water, or that held by the adhesion to the soil particles, and which 

 fills the openings between the particles; and third, hygroscopic 

 water, or that held firmly by the particles of soil. Land is too wet 

 for growing plants if there is too much free or running water, or 

 if the water level is near the surface, as it prevents the circulation 

 of the air and the penetration of the roots to sufficient depths. 



Plants do not, as a rule, use the running water; they are able 

 to obtain all they need when land is moist rather than wet. For 

 this reason the water in soils useful for plants is usually referred 

 to as the moisture rather than the water of the soil. This moisture 

 of the soil is really, therefore, the capillary water, or that held by 

 adhesion to the soil particles, and while there may be too much 

 capillary water in soils for the best development of plants, because 

 certain kinds of soils may absorb too much, it is not usually a serious 

 matter, because the difficulty can be readily remedied, as will be 

 pointed out later. 



The hygroscopic water is that which is very slow to escape, in 

 fact, it must be driven out of the soil. That is, soil w^hich appears 

 to be absolutely dry may still contain this hygroscopic water, and 



