cates of the same treatment than it was 

 between adjoining treatments. 



Dry weight of fohage appeared to be a 

 sUghtly more sensitive indicat^or of response 

 to treatment than average height or height 

 growth. 



Figure 1. — Variation in foliage dry weight is 

 often greater between treatment replications 

 than between adjoining treatments. Here the 

 horizontal lines show the range in dry weight 

 with the mean indicated. 



N-P-K TREATMENT 



300 900 1500 2100 2700 



AVERAGE DRY WEIGHT IN MILLIGRAMS 



Element Content 



As the supply of nitrogen increased, so did 

 the percent nitrogen content in the fohage 

 (table 2). Variations in the content of either 

 phosphorus or potassium in the fohage were 

 much less apparent although the content of 

 these elements tended to increase slightly 

 with increasing suppUes. 



Response Surface Analysis 



A response surface analysis of both average 

 height and of average dry weight indicated 

 that the optimum level of potassium was not 

 tested. However, within the range of concen- 

 trations tested, the optimum levels were: 



Nitrogen 

 p.p.m. 

 Average height 500 

 Average dry 



weight 326 



Phosphorus Potassium 

 p.p.m. p.p.m. 

 78.3 88.4 



60.1 



67.5 



Discussion 



The results of this study suggest that paper 

 birch seedUngs are more responsive to changes 

 in nitrogen supply than they are to changes 

 in phosphorus and potassium supplies. Within 

 the conditions of the study, the better height 

 growth and average dry weight of foliage were 

 associated with 400 p.p.m. and 600 p.p.m. N, 

 50 and 75 p.p.m. P, and almost any concen- 

 tration of K. 



The effects of these elements were not 

 greatly different, whether appUed in combina- 

 tion or singly. However, the concentration of 

 N giving the most favorable growth response 

 was greater where N was supplied in combi- 

 nation with P and K than where N only was 

 supphed. Nitrogen was the only element for 

 which the foliar content appeared strongly 

 related to supply. 



The optimum combination of these ele- 

 ments was not defined by this study. Inge- 

 stad (5), working with Betula verrucosa 

 Ehrh., reported that the optimum proportions 

 of N., P, and K should be in the ratio of 



Table 2. — Percent confenf of nitrogen, phosphorus, 

 and potassium in the foliage of paper birch 



seedlings, by treatnient 



N-P-K 

 treatment 





Foliage content 





N 



P 



K 





Pet. 



Pet. 



Pet. 



64-50-70 



1.4 



1.6 



1.8 



200-25-35 



2.8 



1.4 



1.2 



200-25-105 



2.8 



1.7 



1.7 



200-75-35 



2.8 



2.0 



1.3 



200-75-105 



3.0 



1.8 



2.2 



400-8-70 



3.8 



1.6 



1.4 



400-50-11 



4.0 



1.7 



.7 



400-50-70 



3.9 



1.7 



1.6 



400-50-129 



3.8 



1.6 



2.5 



400-92-70 



4.4 



2.4 



1.8 



600-25-35 



4.9 



.9 



.9 



600-25-105 



5.0 



1.2 



1.5 



600-75-35 



5.5 



1.3 



.9 



600-75-105 



5.1 



1.5 



1.6 



736-50-70 



5.3 



1.4 



1.2 



3 



