34 



Development and Activities of Roots of Crop Plants. 



Shantz (1912), at least to a depth of 4 or 5 feet. On the other hand, during 

 7 years of field work in many States, the senior writer has never found the 

 water-content to fall below the hygroscopic coefficient, except in the surface 

 soil, where direct evaporation rather than absorption by plants was the cause. 

 These findings are quite in agreement with those of Alway and others (1919). 

 However, it should be made clear that we are not at all certain that crop 

 plants are as efficient in exhausting the water-supply as is native vegetation. 

 Moreover, it may be found that certain plants of either group are more or 

 less efficient than others. The thorough distribution of a minutely branched 

 root system through all parts of the soil, as already described, would promote 

 efficient absorption. 



In figure 12 the available water-content of the soil is given to a depth of 

 3 feet from March 31 to June 16. A glance at this figure shows clearly the 



o ' i i — * 



Fio. 13. — Water-content in excess of hygroscopic coefficient 

 in the several crop plats on May 30. 



rather uniform distribution of moisture, as well as the fact that practically 

 throughout the entire period a minimum of 14 per cent was available at 

 all levels. Since the hygroscopic coefficients of these soils vary from 8.9 

 per cent (surface 6 inches) to 9.2 per cent (fourth foot), the actual water-content 

 for the period did not fall below 21 per cent. These data are from an open 

 space 10 feet square in the corn plat. Water losses here were by surface 

 evaporation only. Later in the season the area was occupied in part at least 

 by the widely extending roots of the corn, and further water-content deter- 

 minations were not made. 



The water available to the various crops at the several levels on May 30 

 is given in figure 13. At this time no marked differences in the water-content 



