PREHARVEST APPLE DROP 



surface. Furthermore, there is considerable variation in the thick- 

 ness and distribution of the different soil zones located above the till 

 layer. It was thought that these factors might cause differences in 

 the size and distribution of the root system of different trees ; also in 

 the ability of different trees to obtain water and nutrients, which, in 

 turn, might have an influence on the ability of the fruit to remain 

 attached to the tree. For these reasons soil profile studies were made 

 to determine the difference, if any, in the number and size of roots, 

 and of the root distribution of these trees in the different soil zones; 

 also to observe any dift'erence in the distribution and extent of the 

 several soil layers and the possible relation to root distribution and 

 tree performance. 



In June, 1938. excavations 10 feet long and 2 feet wide were made 

 at a distance of eight feet from the north side of the trunk of each 

 tree. The depth of each excavation was determined by the underlying 

 hard till layer, and digging was stopped after penetrating several 

 inches into this layer. Because of the lack of uniformity in the depth 



Fig. 1. Distribution of Roots and Profile Zones under tree 

 No. 18 (upper) and tree No. 8 (lower). 



A, B, C, D, E indicate soil zones as described in the text. Relative size of 

 roots is indicated by dots and circles. Small dots represent roots 2 mm. or less 

 in diameter. Both charts represent light-dropping trees. 



