CHAPTER VIII 



SOIL WATER AND ITS RELATION TO SOIL FERTILITY 



Water is a most important though variable factor affecting 

 soil fertility. Crop yields may be much reduced by a lack of water 

 or by too much of it. The life processes and special activities of 

 plants as well as of animals are at all times dependent on the 

 water supply. 



Why Plants Require Water. — In relation to plants, water 

 serves a number of purposes, as — 



a. A nutrient. It may without change become a part of the 

 plant cell, or it may contribute to the making of foods. 



6. A carrier for plant-food elements and plant-food. The salts 

 of the soil which contain nitrogen and the mineral elements, 

 and the carbon dioxide of the air, which contains the carbon must 

 be brought to the leaf cells in soluble form before they can be 

 utilized in food manufacture; and when the foods are made, they 

 are translocated within the plant in soluble form by means of 

 water (p. 50). 



c. To keep the cells turgid, or expanded, to prevent wilting. 

 When plants cannot get all the water they need they wilt, and when 

 they remain wilted they die. 



d. A cooling agent. The evaporation of water from the leaves 

 prevents their getting too warm. It has been found that even 

 with evaporation the leaf temperature may be ten to fourteen 

 degrees higher than that of the surrounding air. 



e. An aid in life processes. Water is necessary to permit of 

 certain physical and chemical changes (life processes) within 

 the plant. 



Further Importance of Water. — ^Water is a great solvent in 

 soils, and without it the necessary chemical changes in soils cannot 

 take place; nor can the helpful soil organisms develop and do their 

 work without moisture. 



Crops Require Much Water. — Crops require tremendous 

 amounts of water; for example, in a humid climate like that east 

 of the Missouri River, about 152 barrels of water are required 

 to produce one bushel of corn (Fig. 37). This means that in the 



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