SOIL MOISTURE 



63 



bution was influenced but little in this particular case. Cultivation is 

 mentioned often as a means of forcing deeper rooting of fruit trees and 

 sod culture as encouraging shallower rooting. These practices often 

 have these effects, but they may have no such effect, as in the Ohio investi- 

 gation cited, or they may have the opposite effects, as in Hood River. 

 This brings out the point that tillage methods as such are not to be 

 regarded as direct means of influencing root distribution, but as means 

 of altering the physical and chemical condition of the soil and thus indi- 

 rectly leading to shallow or deep penetration. Root growth and distri- 

 bution is a response to these physical and chemical conditions. It is 

 noteworthy that in the Hood River orchards many of the symptoms of 

 drought injury were associated with extreme shallow rooting — premature 

 dropping of the foliage, dieback and fruit-pit. 



Interesting data concerning the effect of cultivation on root distri- 

 bution are afforded by the figures in Table 32. Cultivation along one 

 or both sides of the tree row reduced the absolute lateral spread and the 

 ratio between the lateral spread and height of the trees. The greater 

 reduction accompanied cultivation along both sides. In the cultivated 

 soil the tree roots did not have to range so wide to meet the actually 

 increased water requirements of the trees as in the uncultivated land. 

 Incidentally the figures in Table 32 throw some light on the lateral 

 spread of tree roots as compared with the spread of their branches. 

 Though spread of top is not given it is reasonable to assume that in this 

 species it is less than tree height. It is often said that the lateral spread 

 of the roots is about equal to the lateral spread of the branches. In 

 uncultivated ground it was in this instance more than twice as great. 



Mason^^ cites an instance in which the olive grown in an extremely dry soil 

 and climate had a root system radiating 10 to 11 feet in nearly all directions when 

 the top was only 6 feet in height, had a spread of only 7 feet and a trunk diameter 

 of 3% inches. In this case there was a total of 185 feet of roots 3-8 inch or 

 more in diameter and the area occupied by roots of this size was about nine 

 times that of the spread of the branches. This fruit as it grows in the Sfax 

 region of Northern Africa furnishes a good illustration of the adaptation of the 

 root system to moisture conditions. There it sends out numerous roots which 

 run for long distances comparatively close to the surface where they can make 

 use of the moisture that penetrates only a few inches into the ground at the 

 time of the infrequent light rains. 



