1. Effects of land management on carbon and nitrogen in soils from New Zealand
Jess Holcomb1, Kate Lajtha2
Oregon State University, Corvallis, OR 97331
1. Bioresource Research, 2. Department of Botany and Plant Pathology

2. Background Land Conversion Removes Vegetation Switches Vegetation
Effects Organic Matter in soil
Effects root organic matter
(Dr. Troy Baisden, 2008)

3. Background Global Warming Increase in CO2 Industry Automobile Exhaust
Energy Production
Burning
Making Cement
(Library of Congress, 2008)

4. Background Carbon (C) in the Environment Ocean Soil Atmosphere
Vegetation
(NASA, 2004)

5. Background Why is soil C different Horizons C loss C sequestration O A
Decomposition
C sequestration
Dark parts of soil
Organic matter
Soil organic matter
Humic matter
(USDA, 2006)

6. Background Nitrogen (N) Most limited Nutrient Determines plant growth
Negative Charge, easily lost
(EPA, 2004)

7. Background Organic Matter
Grass
Easier to decompose
Low C:N ratio
Less Fats and waxes
Pine
Waxes
High C:N ratios
Lignin
Harder to decompose
Large pieces

8. Background Plots New Zealand Same Watershed 3 Plots Native Pasture
Pine Plantation
(Dr. Troy Baisden, 2008)

9. Podocarp Native Control Large Podocarp Trees 500-800 years old
Southern Hemisphere conifers
years old
No logging
(Dr. Troy Baisden, 2008)

10. Pasture Cleared in 1920 to scrub Turned into pasture 1957
P fertilizer and clover for N
Grazed
Sheep
Cattle
(Dr. Troy Baisden, 2008)

11. Plantation Pine Turned pasture to pine in 1973 2200 trees per ha
Pinus radiata
2200 trees per ha
Fenced
No Grazing
Understory
Ferns and native shrub
(Dr. Troy Baisden, 2008)

12. Problem How will land management affect soil C and N
What density fraction is losing/gaining soil C and N

13. Hypothesis Loss of C in pasture Increase in soil N in pasture
Loss of stable soil C
Increase in soil N in pasture
Legumes planted
Increase of C in pine plantation
Introduces stable organic matter

14. Methods Samples taken from 0-15 cm Soil was air dried
Below litter layer
Soil was air dried
Soil was passed through 2mm sieve

15. Methods
Samples Sequentially Fractionated with Sodium Polytungstate (SPT)
Very dense salt
Used to separate soil particles based on density
Density correlates with organic matter
More organic matter, less dense

16. Methods Fraction Interpretation
Light
New organic matter
Not much decomposition
Middle
More stable, broken down organic
Heavy
Mineral, silt/sand
(Glazer, 1995)

17. Methods Densities of 1.65 g/ml 1.85 g/ml 2.00 g/ml 2.40 g/ml 2.65 g/ml
>2.65
2.0
(Sollins, 2006)

18. Methods Soil was suspended in SPT solution
Shaken, centrifuged to separate densities
Floating fractions were aspirated off of the surface
Fraction was rinsed
Removes SPT
Dried in oven to remove moisture
(Newmans Own, 2008)

19. Methods Samples Ground Run on Leco CNS 2000 for C and N
IR absorption for C
Molecules absorb IR
Thermal conductivity for N
Ability to conduct heat
(St. Mary’s University, 2008)

20. Results Fractions similar in mass
1.65, 2.4, 2.65 showed greatest variation
Variation only due to one sample

21. Discussion Dry Mass was as expected
All fractions similar in dry weight
Same soils, only difference is organic matter/quality
Effects the amount of C and N in each fraction

22. Results Nitrogen Carbon Least Least Native Pasture Pasture Native
Plantation
Most
Carbon
Least
Pasture
Native
Plantation
Most

23. Results Similar for most fractions
Major difference in the 2.4 fraction

24. Discussion Native Pasture Plantation Pine Carbon
Stable C, hard to decompose
Pasture
Loss of stable C, introduction of labile C, unstable lost quickly
Plantation Pine
Re-introduction of stable C, leads to increased C pool

25. Results
Similar across fractions
Major difference in 2.4 fraction

26. Discussion Native Pasture Plantation Pine Nitrogen
N is sparse, limited N inputs
Pasture
Clover fixes N, increases N in system
Plantation Pine
N from clover taken in by pine, more stable matter, N last longer in system

27. Results Native highest C:N
Plantation next highest C:N except in 2.4, >2.65

28. Discussion C:N Due to mass of C and N
Results match with mass of C/N for each treatment
Pasture lower C:N due to vegetation
Low C:N Plantation Pine at 2.4 due to increase N at this fraction
N in stable soil organic matter

29. Discussion Each graph is similar to the others
Spike at 2.4 is seen in all of them
Due to increased fraction mass at 2.4
Difference in dry ~ 2.2 g (between Native/Plantation)
Difference in C ~ 1.2 g (between Native/Plantation)
Difference in N ~ 0.11g (between Native/Plantation) C:N ~10

30. Conclusions Conversion to pasture reduces soil C
Increased N in pasture and Plantation Pine due to legumes
Conversion to Plantation Pine increase soil C
Soil C changes due to stable forms of soil organic matter

31. Future Research Deeper Samples Analyzed
Tree roots may run deeper than grass
Results in loss of organic matter when removed

32. References
P.N. Beets, G.R. Oliver, P.W. Clinton Soil carbon protection in podocarp/hardwood forest, and effects of conversion to pasture and exotic pin forest. Environmental Pollution 116: S63-S73.
L.A. Schipper, W.T. Baisden, R.L. Parfitt, C. Ross, F.F. Claydon, G. Arnold Large losses of soil C and N from soil profiles under pasture in New Zealand during the past 20 years. Global Change Biology 13:
R.L. Parfitt, N.A. Scott, D.J. Ross, G.J. Salt, K.R. Tate Land-use change effects on soil Cand N transformations in soils of high N status: comparisons under indigenous forest, pasture and pine plantation. Biogeochemistry 66: