1. Predicting Nitrogen Fertilizer Response in Douglas-fir Plantations Kim Littke Rob Harrison

2. Introduction  Nitrogen fertilization is a common practice in forests of the Pacific Northwest  The Regional Forest Nutrition Research Project was implemented in the 1960s to study the effect of N fertilization over western Washington and Oregon  However, growth response to N fertilization was widely variable

3. Introduction  Growth response appears to be related to forest N pools and fluxes  Large N pools and fluxes will probably be unresponsive to N fertilization  Small N pools and fluxes should be responsive –Unless water or other nutrients are limiting

4. Hypotheses  Soil nitrogen content down to one meter is the biggest predictor of growth response to N fertilization  Low soil water availability hinders growth response in stands that should otherwise respond to N fertilization

5. Sites  15-25 year old Douglas-fir stands in British Columbia, Oregon, and Washington  Located in Sitka spruce and western hemlock vegetation zones  Range of landform, elevation, and position on slope  Sedimentary, igneous, and glacial parent materials

6. Paired Tree Installations

7. Add Beyond Nitrogen Installations

8. Plot Treatment Design

9. Materials and Methods  Measure height, DBH, height to live crown, and known environmental gradients  Pair trees by most similar DBH and crown height  Fertilize one tree of each pair with 224 kg N/ha  Determine LAI, elevation, slope, aspect, and slope shape

10. Sampling Methods Background  Measure precipitation using rain gauges  Measure soil moisture and temperature  Determine soil N and C content to one meter  Determine C and N content of litter Post-fertilization  Sample soil under trees for input of N  Collect current foliage

11. Nutrient Analysis  Determine soil bulk density and rock content  Soil and litter will be analyzed for nutrient concentrations  Total nutrients estimated to one meter  Foliar weight and nutrition will be determined

12. Tree Pairings

13. Soil Pits Armstrong Janicki Sand Clarks Creek DF Clay

14. Sensor Installation  Soil moisture and temperature sensors placed horizontally at 5 and 50 cm  Air temperature and humidity at 15 cm above the forest floor  Rain gauge 25 cm above forest floor

15. Soil Moisture

16. Field Capacity vs. Wilting Point

17. Soil Nitrogen to 1 Meter Glacial North to South SedimentaryIgneous

18. Soil Carbon to 1 Meter Glacial North to South SedimentaryIgneous

19. Statistics  Sedimentary soils significantly greater soil C and N content (p=0.025 and 0.001).  Glacial soils significantly greater soil CN ratio (p=0.003)

20. Current Work  34 installations fertilized since spring 2009  56 total installations  Soil sampled and sensors at 53 installations  Two year measurements this fall for 6 installations

21. Future work  Develop model to predict which stands will respond to N fertilization  Range of background N and water availability  Previous growth –PAI –Earlywood to latewood ratio  Foliage size and weight –Differences over water and N availability –Change after fertilization

22. Questions?