EXPERIMENTAL PROCEDURES IN TREE FERTILIZATION 



The experimental area (Fig. 1 ) used in our tests of 

 shade tree fertilization was located on the grounds of the 

 Morton Arboretum near Lisle. Illinois. This area is ap- 

 proximately 25 miles west of Chicago. It has a 2' \ in r 

 slope to the south and 7 to 14 inches of topsoil. The soil 

 is classified as Andres silt loam (293). 



An Illinois soil survey report (Wascher et al. 19' 

 characterized this soil as follows: "Andres is high in or- 

 ganic matter, medium to slightly acid, low in available 

 phosphorus, and about medium in available potassium. 

 Water-holding capacity is high but moisture movement 

 within the silty clay loam till is somewhat si: w." 



in a representative profile of Andres silt loam, the 

 surface soil is black to very dark brown friable loam to 

 silt loam, fine crumb to granular structure; 10 to 16 inches 

 thick. The subsurface soil is very dark brown to very 

 dark grayish-brown friable loam to silt loam; weak, very 

 fine subangular blocky structure; 3 to 6 inches th' ':. The 

 subsoil is very dark grayish-brown to yellowish-brown firm 

 clay loam to sandy clay loam with a few small pebbles; 

 weak, medium subangular blocky structure; neutral; 12 to 

 20 inches thick. 



Soil samples collected in November, [964, from 15 

 sites in the check areas at 12- and 24-inch depths were 

 analyzed by the Department of Floriculture at the Uni- 

 versity of Illinois using the Bray method. From samples 

 taken at the 12-inch depth, the pH readings averaged 6.81; 

 the phosphorus averaged 14.5 and the potassium 189 

 pounds per acre. At the 24-inch depth, the pH readings 



averaged 6.96; die phosphorus averaged ".2 and the potas- 

 sium I i] pounds pei acn Samples taken in the tall oi 

 at a 6-inch depth averaged 32 pounds "t nil 



per acre. In 1964, the nitrogen analysis at the 12-inch 

 depth ranged from a high of Is pounds per acre down to 

 a trace. 



Three species of trees growing on the experimental 

 a"ea were used in the tests: pin oak (Quercuj palustril 

 h.), whne ash (Fraxinus americana L), and honey 

 thoi I., var. inermis Pursh). The 

 trees had been planted in square blocks with 15- to 20-foot 

 Spacing distances between trees and 25 feet between blocks. 

 Each block originally contained 100 trees of a single species. 

 The oak and ash had been transplanted to the experimental 

 area in 1956, the locust in 195 7 . When transplanted, the 

 oaks were 1 to s feet tall, the ashes I to 6 feet tall, and 

 the locusts 3 to -1 feet tall. Twelve oaks were planted on 

 the area in 1958 to replace oaks that had died. Since sev- 

 eral locusts were missing, it was necessary to use trec^ in 

 two blocks to obtain the desired number for the test. 



All blocks had been planted with Kentucky bluegrass, 

 Poa pratensil I... and a sod had been maintained with occa- 

 sional mowing each summer. In the spring of 1963 when 

 the fertilizer tests were started, the oaks averaged 1.64 

 inches dbh and 10 feet tall, the ashes 2.9-1 inches dbh and 

 14 feet tall, and the locusts 1.74 inches dbh and 10 feet 

 rail. 



Four methods of application and several fertilizers were 

 used in 16 different combinations (Table 4), each com- 

 bination designated as a treatment. Each block of trees 





FIG. 1. — Part of plot of pin oak trees in the experimental area used lor the investigation reported lure. Tins is one ol the four 

 test plots located at the Morton Arboretum. I. isle. Illinois. The picture was taken in April. 1965. 



