Predicting Nitrogen Fertilizer Response in

Douglas-fir Plantations

Kim LittkeRob 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

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

Paired Tree Installations

Add Beyond Nitrogen Installations

Plot Treatment Design

10 meters

15 meters

542 3 6

11108 9 12

171614 15 18

232220 21 24

1

7

13

19

25 292826 27 30

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

6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.015.0

25.0

35.0

45.0

55.0

65.0

Steel Creek

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

DBH (in)

Cro

wn

He

igh

t (f

t)

1

3

4

5

2

6

15

9

14

17

18

7

8

10

11

12

13

16

19

Soil PitsArmstrong JanickiSand

Clarks Creek DFClay

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

11/3/08 12/23/08 2/11/09 4/2/09 5/22/090.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

Clayey 5 cmClayey 50 cmSandy 5 cmSandy 50 cm

Date

Soil M

ois

ture

(m

3/m

3)

Field Capacity vs. Wilting Point

0 5 10 15 20 25 30 35 400

5

10

15

20

25

30

35

40f(x) = 0.916796224319822 x + 7.47159911160467R² = 0.779803775528582

AllLinear (All)ClayLoamySandySandy loam

Wilting Point (m3/m3)

Fie

ld C

ap

aci

ty (

m3

/m3

)

Soil Nitrogen to 1 Meter

0

5000

10000

15000

20000

25000

30000

Nit

rog

en

Co

nte

nt

(kg

N/h

a)

GlacialNorth to South

Sedimentary Igneous

0

100

200

300

400

500

Carb

on

C

on

ten

t (M

g C

/ha)

Soil Carbon to 1 Meter

GlacialNorth to South

Sedimentary Igneous

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 installationsSoil sampled and sensors at 53

installationsTwo 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?