6 STATION BULLETIN 355 



of the upper boundary of the till layer, the trenches were necessarily 

 of different depths. Charts were made of the treeward side of each 

 excavation, indicating thereon the contours of the different soil zones 

 and the position and diameter of all exposed roots which were severed 

 during the excavation. The actual diameter of each root 2 mm. or 

 over, was so designated on the charts, the smaller roots as "less than 

 2 mm." The profile charts for excavation under two of the trees are 

 shown in Fig. 1. 



A. Physical 



The soil layers, or zones, encountered are designated by letter 

 and are described as follows : 



Zone A. Top soil, dark brown loam ranging in depth from 2.9 

 to 8.5 inches and under one tree 14.1 inches. 



Zone B. Brown, mellow loam down to an average depth of 9 

 inches, ranging from 5.9 to 15.3 inches below the soil surface. 



Zone C. Yellowish brown to rusty yellow-brown sandy loam of 

 crumb structure, down to an' average depth of 16.5 inches, rang- 

 ing from 11.1 to 29.0 inches below the surface. 



Zone D. Slightly olive-yellow material of crumb structure, with 

 many small and some large stones, also coarse and fine gravel, 

 to an average depth of 43.6 inches, ranging from 18.1 to 61.2 

 inches below the soil surface. 



Zone E. Olive to grayish green, hard platy till ; the top of this 

 layer averaged 31.6 inches below the soil surface, ranging from 

 11.9 to 61.2 inches ; the thicknes sof this layer was not determined. 



Occasional pockets of fine gray sand were encountered in some 

 of the excavations. 



The A. C, and E layers were universally present in the block ; 

 the stony D layer was absent under 8 trees located on the lower slope 

 of the orchard ; the mellow B layer was absent under 5 of the trees. 

 Dift'ercnces in drop cannot be accounted for by diff'erences in zone 

 thickness (Table 3), and there was apparently no correlation between 

 the al^sence of any of these layers and the amount of fruit dropping. 



Table 3. Average Thickness Soil Zones (Inches) 



Since water and nutrients are absorbed principally through the 

 root hairs, the greatest interest lay in a study of roots less than 2 mm. 

 in diameter. For each tree a summary of the total number of roots 

 less than 2 mm. in diameter exposed by the excavations is presented 



