54 FUNDAMENTALS OF FRUIT PRODUCTION 



For instance, in one experiment on a heavy soil in California, after an 

 irrigation considered sufficient to last about four weeks, the moisture 

 was found to have penetrated laterally only about eighteen inches from 

 the irrigation furrow. ^^ Figure 3 shows graphically the rate of this 

 lateral spread as it takes place through the force of capillarity and unaided 

 by gravity. The spacing of irrigation furrows must be made accordingly, 

 if the entire volume of the soil is to be wetted. It is for this reason that 

 basin irrigation or flooding is sometimes preferred to furrow irrigation in 

 comparatively heavy land. 



THE DISTRIBUTION OF FRUIT TREE ROOTS AS INFLUENCED BY SOIL 



MOISTURE 



The size and distribution of the root system depends upon the opera- 

 tion of many factors, such as the moisture supply, aeration of the soil 

 and nutrient supply. In most cases it is impossible to assign to each 

 factor the part it has played, but as they are more or less interdependent 

 they may be discussed together. 



The Ideal Root System. — Deep rooting is desirable for the purpose 

 of making the water (and nutrient) supply contained in a large volume 

 of soil available to the plant. For the same reason there should be at 

 least a moderate lateral spread. In other words the tree, or other 

 fruit-producing plant, that is equipped with an extensive root system 

 will be able better to endure extremes of drought or temperature or 

 exceptional demands for a supply of nutrients, than one with a limited 

 root system. Plants grown in a comparatively concentrated nutrient 

 solution or in rich soil have roots that are shorter, more branched and 

 more compact than those grown in a weak nutrient solution or in a 

 poor soil. Changing fertility is one explanation of the marked contrasts 

 in the degree of ramification of roots as they penetrate different strata. ^^ 

 The ideal root system is, therefore, not the one with branches that reach 

 out or down the farthest, but the one that more or less fully explores 

 and occupies the soil to a reasonable depth and within a reasonable 

 radius. Otherwise, it would be necessary to regard the root system pro- 

 duced only in an infertile soil as the ideal. 



Specific and Varietal Differences in Root Distribution. — Depth of 

 rooting and lateral spread of roots depend in the first place on the species 

 or variety of plant., Some, like the walnut and pecan, are character- 

 istically deep rooted; others like the spruces and hemlocks and the river 

 bank grape {Vitis riparia) are characteristically shallow rooted. The 

 roots of certain fruit varieties, like the Wealthy apple, are strong, stocky 

 and far ranging; those of other varieties, like certain strains of the Doucin, 

 are short, slender, compact and much branched. These characteristics 

 should be borne in mind when selecting fruits or fruit stocks for particular 



