CHAPTER VIII 

 WATER IN SOILS 



IT is difficult to comprehend the importance of water in soils. 

 Not only must the water be present in the right amount, but the 

 condition in which it exists during the growth of plants affects 

 their development. The annual rainfall in any region may be 

 abundant for the growing of crops if it were distributed evenly 

 throughout the growing season. It is found that in many sec- 

 tions of this country the greatest rainfall is during the dormant 

 season, and much of the growing season is without sufficient rain. 

 Long dry periods are frequent during the summer when plants 

 are in greatest need of water to maintain their rapid growth. 



Water Required During the Growing Season. Much of the 

 rain which falls during winter or when there are no plants growing 

 upon the fields may be lost by running off or percolating to great 

 depths. Much less of the rain which falls during the spring and 

 summer, when growing plants occupy the field, will be lost. 



By 5 a number of trials King showed that the average amount 

 of water used by various crops during their growth, to produce 

 one ton of dry matter, was as follows: Oats, 504 tons, or nearly 

 40 inches; Barley, 464 tons, or nearly 21 inches; Clover, 576 tons, 

 or 22 inches; Potatoes, 385 tons, or nearly 24 inches; average of 

 these four crops, 482 tons, or 27 inches. The number of inches of 

 rainfall is not proportional to the tons of water for a ton of dry 

 matter, because of the variation in yield in these crops. 



Average Annual Rainfall. The average annual rainfall in the 

 humid sections of this country is much greater than this average. 

 The Pacific Coast of Oregon and Washington has fifty to sixty 

 inches of rainfall annually. This amount is also found in the 

 southeastern states, along the coast from Louisiana to Virginia. 

 It exceeds forty inches throughout the eastern states as far west 

 as southeastern Kansas. Oklahoma and eastern Texas. In most 

 of the region west of Minnesota and the western third of Nebraska, 

 Kansas and Texas the annual rainfall is twenty inches or less. As 

 we go westward this amount is seldom exceeded in any locality 

 until we reach the central lines of Oregon and Washington, and 

 the western line of Nevada. 



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