Table 6. — Soil characteristics associated with the difference between released and predicted nonreleased growth 







Significance 







Regression coefficients 









Time period since release 







Time period since release 









(years) 







(vears) 





Variables 



0-5 



5-10 



10-15 



0-5 



5-10 



10-15 



Orn^nir matter (°/n\ 



NS 



NS 



INO 



MCI 



1 N O 











NS 



INO 



1 N O 









Flpptrippl cnnci I u mho^l 



l_ J I 1 1 L/ Ct 1 !U. \ LI 1 1 1 1 1 \J O ) 



NS 



MS 

 1 NO 



MC 

 1 N O 









Rnrnn Inning 



DUI \J\ 1 \^J|JIH) 



NS 



MC 

 INO 



MS 



INO 









~7\r\r fnnm\ 



NS 



NS 



INO 



MS 



INO 









Mannanpsp t'nnrrh 



NS 



NS 



1 N O 



MS 



INO 











0.0031 



n nnni 



n nnm 





A ft7A1 



— O.DkJHO 



Ammonium /nnrrii 



NS 



NS 









.uoou 



nilialr \yjyj\\\i 



NS 



nnm 



MS 



INO 





9A77 







.0001 



.0001 



MS 



INO 









Copper (ppm) 



.0001 



.0001 



NS 



- .8020 



- .9213 





Potassium/100 (ppm) 



.0001 



.0001 



.0001 



.0599 



.1256 



.0471 



Iron (ppm) 



.0263 



.0001 



NS 



- .0010 



- .0045 





pH 



.0001 



.0001 



.0001 



-1.4210 



-3.1132 



- 1.0853 



Predicted growth 



.0004 



.0001 



.0001 



.1792 



.2742 



.3295 



Intercept 









7.1217 



16.1760 



- .3380 



R 2 









.34 



.49 



.31 



'NS = nonsignificant (P < 0.05) 

 Coefficients not estimated for nonsignificant variables. 



Table 7.— Selected models to test interactions between soil nutrients 



Model Form: In (DDS "released") - In (DDS "nonreleased") = Predicted growth + variable (1) + variable (2) 

 + variable (Invariable (2) 



Significant regression coefficients 

 Time period since release (years) 



Variable interaction 0-5 5-10 10-15 



Total N*K NS' -0.2780 -0.2857 



Total N*Sulfate NS NS NS 



Total N*Cu NS 2.4658 NS 



Total N*Fe 0.0220 .0317 NS 



Total N*pH NS NS NS 



Total N*Ammonium NS NS NS 



Total N* Nitrate NS -1.9135 NS 



pH'Sulfate NS - .1911 NS 



pH'Cu NS NS NS 



pH'Fe NS .0065 NS 



pH*K .3591 NS NS 



pH*Nitrate NS NS NS 



pH'Ammonium NS NS - .1327 



'NS = nonsignificant (P < 0.05) 

 Coefficients not estimated for nonsignificant variables. 



nutrient uptake (Armson 1965). Stand treatments, such 

 as cleaning, weeding, and thinning, can alter tree- 

 growth nutrient relationships (Zinke 1962; Gagnon 

 1964). Also, methods used to assess fertility of agri- 

 cultural soils when used for forest soils may result in 

 erroneous data (Waring and Youngberg 1972). To 

 better assess soil fertility of forest soils, Leaf and 

 Madgwick (1960) suggested modifying agricultural soil 

 tests by including soil volume to better express soil 

 fertility. 



Because of these problems, total quantities of soil 

 nutrients in forest soils can seldom be related easily to 

 tree growth (Ralston 1964) as shown by Ballard and 

 Pritchett (1975) and Pritchett and Llewellyn (1966). For 

 these reasons it is important to evaluate carefully the 

 diameter growth response of western redcedar in rela- 

 tion to soil nutrient quantities. The regression models 

 provided evidence that certain soil nutrients were 

 related to the release response of western redcedar. 



11 



