deuber: soil fertility and root development 
77 
down in the hurricane gave ample evidence of the great concentration 
of the roots of this species in the upper two feet of soil. 
One of the most beneficial effects of fertilization is the stimulus to 
more abundant root formation particularly of the small, much branched 
feeding roots. This occurs with crop plants and trees. A striking 
demonstration of the pronounced effect of sodium nitrate upon root 
branching of various crop plants was secured by Weaver and his co¬ 
workers 1 (1922). Plants were grown in soil fertilized in bands at various 
depths, the fertilized layers being eparated by soft wax seals from the- 
adjoining soil to prevent diffusions of the nitrate salt. The roots pene 
trated the wax seals readily and no matter how near the surface nor how 
deep the fertilized layer the greatest branching of roots occurred in the 
fertilized layer. In some forest nursery investigations Wahlenberg 2 
(1929) modified the root systems of pine transplants to a deeply rooting 
type by placing fertilizer well below the soil surface. It is also possible 
to encourage deeper rooting of established trees by the proper placement 
of the fertilizer and to extend the lateral development of feeding roots 
by placing fertilizer beyond the most concentrated area of roots which 
usually occurs within several feet of the trunk. 
To secure placement of fertilizers below the surface layers of the soil 
for established shade trees various methods are available. The most 
widely used method in New England has been the making of holes 18 
inches to 2 feet deep with a crowbar. These holes are made in circles 
about 30 inches apart beginning near the trunk and extending out be¬ 
yond the spread of the branches. A charge of solid fertilizer is then 
placed in each hole and the holes left open or closed. This type of place¬ 
ment of mixed fertilizers containing phosphorus is of particular value in 
getting the phosphorus in the vicinity of the tree roots since this nu¬ 
trient diffuses to a very limited extent laterally or vertically. The 
crowbar method permits the use of organic materials such as pulverized 
manure, bone meal, blood or tankage which extend the period over which 
the nutrients become soluble and aid in the retention of moisture and 
probably has a beneficial effect upon the micro flora of the soil. 
In recent years there has been an increase in the use of methods for 
injecting dilute solutions of soluble fertilizers into the soil under pressure. 
These methods have much to recommend them for placing quickly 
Weaver, J. E., F. C. Jean and J. W. Crist—Carnegie Inst. Washington Pub. 
316. 1922. 
Wahlenberg, W. G., U. S. Dept. Agr. Cir. No. 125. 1929. 
