Predicting Nitrogen Fertilizer Response in Douglas-fir Plantations Kim Littke Rob Harrison
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
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
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
Sites 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
Paired Tree Installations
Add Beyond Nitrogen Installations
Plot Treatment Design
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
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
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
Tree Pairings
Soil Pits Armstrong Janicki Sand Clarks Creek DF Clay
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
Soil Moisture
Field Capacity vs. Wilting Point
Soil Nitrogen to 1 Meter Glacial North to South SedimentaryIgneous
Soil Carbon to 1 Meter Glacial North to South SedimentaryIgneous
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)
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
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
Questions?