SOIL MOISTURE 55 



soils and when considering the influence of various environmental factors 

 and cultural practices upon root distribution, for though root distri- 

 bution is influenced profoundly there are limits to the plasticity of any 

 species; nothing stated in this connection should be construed as im- 

 plying that these usual limits for the species or variety may be exceeded. 



The Distribution of Tree Roots under Varying Conditions. — Tree 

 roots often range deep, but such investigations as have been reported 

 show a surprisingly shallow root system in most of our orchard planta- 

 tions, at least in the humid regions. 



In the Hood River Valley, Oregon and in Ohio. — For instance a report 

 upon the condition of the root system of apple trees in the Hood River 

 valley states: 



"It was found that the majority of the feeding roots of fruit trees of bearing 

 age were located from 3 to 10 inches below the surface of the soil."^ A discussion 

 of the root systems of apple trees in Ohio includes the following statement: "The 

 main root systems, of apple trees, under the different methods of culture (clean 

 culture with cover crops, sod culture, and sod mulch), were found to be at a sur- 

 prisingly uniform depth — the greater portion of the roots, both large and minute, 

 being removed with the upper 6 inches of soil. . . . The fibrous or feeding-root 

 sj'^stem of a tree under annual plowing and clean culture with cover crops, practi- 

 cally renews itself annually — pushing up thousands of succulent, fibrous rootlets 

 to the very surface of the soil where they actually meet with the steel hoes or 

 spikes of the cultivator or harrow, especially in seasons when moisture is abun- 

 dant. Apparently but a small percentage of these rootlets penetrate the lower, 

 more compact colder soil, but they come to feed where warmth and air and mois- 

 ture combine to provide the necessary conditions for root pasturage. As a matter 

 of fact, these feeding rootlets are cleanly pruned away by the plowshare each 

 succeeding year, and without apparent injury to the trees or crops."" 



The writers then go on to state that the destruction of the roots in 

 the upper 2 or 3 inches of soil by summer drought or by winter cold re- 

 sults in no serious injury to the tree, as those ranging deeper, 4 to 6 

 inches, can take care of the tree's requirements. 



In a Gravelly Loam, Underlaid by Hardpan, in Maine. — Some valuable 

 data on the root distribution of apple trees growing under different soil 

 conditions were obtained by Jones" in Maine. Figures 4 and 5 show photo- 

 graphs of the tree roots obtained from a square foot of soil midway be- 

 tween two Baldwin trees set 27 feet apart and about 28 years old. The 

 photographs show the roots in successive layers of soil 4 inches thick. 

 This soil was a gravelly loam to a depth of 2 or 23^^ feet where a rather 

 impervious hardpan was encountered. Figure 4 shows roots growing in 

 a rather wet portion of the orchard; those in Fig. 5 were from a drier 

 portion. The tops of these trees were not meeting, yet in both the wet 

 and dry areas their roots were interlacing and the soil to a depth of over 

 2 feet was more or less thoroughly exploited. Though the greatest ex- 



