1. Forest Fertilization: Two Topics Roderick Negrave PhD, RPF, PAg Research Section Head, Coast Area MNRO, Nanaimo

2. You Will Hear About: Spring versus fall applications of urea Spring versus fall applications of urea Nitrogen alone compared to N plus P fertilizer applications in western redcedar Nitrogen alone compared to N plus P fertilizer applications in western redcedar

3. Timing of Urea Application What is the issue? Volatilization and leaching losses of N Volatilization and leaching losses of N Reduced recover of N by crop trees Reduced recover of N by crop trees Less efficient use of fertilizer product by the crop Less efficient use of fertilizer product by the crop Increased possibility of environmental contamination Increased possibility of environmental contamination

4. Urea in the Soil Plants cannot absorb urea directly Plants cannot absorb urea directly Urea decomposes to ammonium and then nitrate under appropriate conditions Urea decomposes to ammonium and then nitrate under appropriate conditions Unfavourable condition will promote volatilization of N- based gasses (leaching) Unfavourable condition will promote volatilization of N- based gasses (leaching) Fertilizer-N best applied during periods of rapid fine root growth (spring and fall) Fertilizer-N best applied during periods of rapid fine root growth (spring and fall)

5. General Findings Studies have been conducted on pines and Douglas-fir on the BC Coast, Interior, US Northwest and Scandinavia Studies have been conducted on pines and Douglas-fir on the BC Coast, Interior, US Northwest and Scandinavia Season of urea application has not been studied for western hemlock nor for western redcedar Season of urea application has not been studied for western hemlock nor for western redcedar Studies of Coastal Douglas-fir response are likely most useful for our discussion Studies of Coastal Douglas-fir response are likely most useful for our discussion

6. Applicable Findings Differences in urea-N uptake were found between spring and fall applications Differences in urea-N uptake were found between spring and fall applications Fall applications of urea resulted in greater foliar N concentrations Fall applications of urea resulted in greater foliar N concentrations Foliar concentrations were examined but not growth Foliar concentrations were examined but not growth Less conclusive results in BC Interior Less conclusive results in BC Interior

7. Why? Warmer and drier spring weather conditions promote volatilization of N Warmer and drier spring weather conditions promote volatilization of N Cooler and moister fall weather conditions may promote leaching of N as nitrate Cooler and moister fall weather conditions may promote leaching of N as nitrate However, tree roots are present in sufficient volume to assimilate nitrate before is washes from sites However, tree roots are present in sufficient volume to assimilate nitrate before is washes from sites

8. We Can Conclude... Nitrogen assimilation by stands is likely greater with fall urea applications on the Coast Nitrogen assimilation by stands is likely greater with fall urea applications on the Coast This difference may decrease as sites become more continental This difference may decrease as sites become more continental Effects of seasonal application on growth are uncertain Effects of seasonal application on growth are uncertain

9. Western Redcedar: N Versus N+P Fertilizer Applications Hw responds well to N+P: What about Cw? Hw responds well to N+P: What about Cw? Phosphorus is a pivotal plant nutrient and constituent of cell contents and meristems Phosphorus is a pivotal plant nutrient and constituent of cell contents and meristems Broadly, P found at about 20% of N concentrations Broadly, P found at about 20% of N concentrations Long-term fertilizer responses (>50 yrs) associated with P applications Long-term fertilizer responses (>50 yrs) associated with P applications

10. Sources of Information Weetman et al (2 x 1989): Weetman et al (2 x 1989): One-year of small plot data plus screening trials One-year of small plot data plus screening trials Seven-year old plantation on CH site Seven-year old plantation on CH site Harrington and Devine (2009, 2011): Harrington and Devine (2009, 2011): Thinning and fertilization of a low-site Cw stand on the Olympic Peninsula Thinning and fertilization of a low-site Cw stand on the Olympic Peninsula Fertilizer applied at 1 and 13 years Fertilizer applied at 1 and 13 years Complicated my K, S and Ca application in first fertilization Complicated my K, S and Ca application in first fertilization Followed to 25 years Followed to 25 years

11. Weetman et al. One-Year Height Growth (cm) N0P033 (24) N100P039 (20) N100P10042 (18) N200P045 (21) N200P10050 (20) N300P043 (19) N300P10053 (19)

12. Weetman et al. (cont.) One-year trial suggests Cw response to P likely varies with N application One-year trial suggests Cw response to P likely varies with N application Three-year plot and single-tree screening trials confirmed that Cw does respond to N+P additions Three-year plot and single-tree screening trials confirmed that Cw does respond to N+P additions Significance of difference between N vs. N+P not confirmed but suggested Significance of difference between N vs. N+P not confirmed but suggested

13. Harrington and Devine Volume (Thinned): Volume (Thinned): N: 266.9 (22.7)a N+P: 283.9 (11.5)a Basal Area (Thinned): Basal Area (Thinned): N: 41.8 (2.9)a N+P: 44.3 (1.9)a

14. Devine and Harrington BA PAI (13 – 25 years, thinned): BA PAI (13 – 25 years, thinned): N+P > N Height PAI (13 – 25 years, thinned): Height PAI (13 – 25 years, thinned): N+P >N

15. Considerations Cost of fertilizer-P product Cost of fertilizer-P product Cost of additional turns to deliver added product i.e. 300 kg/h of N versus 300 kg N plus 100 kg/ha of P Cost of additional turns to deliver added product i.e. 300 kg/h of N versus 300 kg N plus 100 kg/ha of P Value of added increment: Marginal return complicated by time and N x P interaction Value of added increment: Marginal return complicated by time and N x P interaction

16. Conclusion There is added growth in N+P compared to N- only applications There is added growth in N+P compared to N- only applications This difference may accelerate over time This difference may accelerate over time Whether additional growth will pay for additional P is likely fairly complex due to complexity of P response with time Whether additional growth will pay for additional P is likely fairly complex due to complexity of P response with time