62 FUNDAMENTALS OF FRUIT PRODUCTION 



probably encounter in the surface layers, shortly after the time of setting, 

 those conditions of air and moisture approaching the optimum for growth. 

 Then as the season progresses and the surface soil dries, the roots in 

 many cases turn down and send branches into deeper layers and a distri- 

 bution is effected resembling that of native plants.®^ This may be looked 

 upon as a kind of adaptation, an accomodative change, to meet new con- 

 ditions of environment. That this change in rooting habit is very largely 

 a response to moisture and aeration conditions is indicated by the fact 

 that with a rise in the ground water table from heavy irrigation the roots 

 are again forced to occupy only a shallow layer of soil. This condition is 

 found in some of the orange groves of California. ^^ Three or four feet 

 beneath the surface the soil is so water-logged that roots will not penetrate 

 and the top 6 or 8 inches are so filled with feeding rootlets that each 

 cultivation results in more or less serious root pruning. Trees under such 

 conditions require heavier irrigation and more fertilization than those 

 with deeper roots and, what is perhaps more important, they are more 

 sensitive to extremes of any kind affecting the roots either directly or 

 indirectly. Consequently they are more exacting in their cultural 

 demands. The same danger from heavy irrigation is met in deciduous 

 fruit production. Thus it has been found in Utah that raising the water 

 table even temporarily by irrigation causes the death of the deeper roots 

 and results in a kind of root pruning or root training and that the general 

 shape of the root system of the tree may be controlled more or less by the 

 distribution of the iri'igation water. ^ One of the most difficult problems 

 in many irrigated sections is to apply the water in such a way that plants 

 are not made surface feeders and the natural advantages of a deep soil 

 lost. 



The Influence of Cultivation. — Allen^ found that tillage methods influenced 

 root distribution in the Hood River district. He reports that where clean 

 culture had been practiced without the use of the plow but with disk and other 

 cultivators "a thick mat of fibrous roots was found immediately below the soil' 

 mulch. ... In the few restricted areas that received neither cultivation nor 

 irrigation, the roots were found to be distributed from near the surface to 1 

 foot and 16 inches in depth. Under sod and irrigation conditions the roots were 

 quite uniformly distributed from near the surface to 23-2 feet in depth." Immedi- 

 ately under the loose surface soil of the cultivated areas he found an impervious 

 hardpan or plowsole had developed, which was dry at the time of this examina- 

 tion. The untilled and irrigated land did not have this hardpan layer. 



Different tillage methods had resulted in great variation in the physical 

 character and moisture content of the soil between the depths of 6 and 

 30 inches, and in corresponding variations in root distribution. Evidently 

 the varying tillage methods used in certain Ohio orchards^* did not 

 change materially the character of the soil below a depth of 6 or 10 

 inches and since few roots developed in it below this depth, root distri- 



