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
Background

Land Conversion
• Removes
Vegetation
• Switches Vegetation
• Effects Organic
Matter in soil
• Effects root organic
matter
(Dr. Troy Baisden, 2008)
Background


Global Warming
Increase in CO2
• Industry
• Automobile Exhaust
• Energy Production
• Burning
• Making Cement
(Library of Congress, 2008)
Background

Carbon (C) in the
Environment
•
•
•
•
Ocean
Soil
Atmosphere
Vegetation
(NASA, 2004)
Background
Horizons

Why is soil C
different
O
A
• C loss

Decomposition
B
• C sequestration




Dark parts of soil
Organic matter
Soil organic matter
Humic matter
C
(USDA, 2006)
Background

Nitrogen (N)
• Most limited
Nutrient
• Determines plant
growth
• Negative Charge,
easily lost
(EPA, 2004)
Background
Organic Matter

Pine
• Waxes
• High C:N
ratios
• Lignin
• Harder to
decompose
• Large pieces

Grass
• Easier to
decompose
• Low C:N
ratio
• Less Fats
and waxes
Background Plots



New Zealand
Same Watershed
3 Plots
• Native
• Pasture
• Pine Plantation
(Dr. Troy Baisden, 2008)
Podocarp Native


Control
Large Podocarp
Trees
• Southern
Hemisphere
conifers


500-800 years old
No logging
(Dr. Troy Baisden, 2008)
Pasture




Cleared in 1920 to
scrub
Turned into pasture
1957
P fertilizer and
clover for N
Grazed
• Sheep
• Cattle
(Dr. Troy Baisden, 2008)
Plantation Pine

Turned pasture to
pine in 1973
• Pinus radiata


2200 trees per ha
Fenced
• No Grazing

Understory
• Ferns and native
shrub
(Dr. Troy Baisden, 2008)
Problem

How will land management affect
soil C and N
• What density fraction is
losing/gaining soil C and N
Hypothesis

Loss of C 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
Methods

Samples taken from 0-15 cm
• Below litter layer


Soil was air dried
Soil was passed through
2mm sieve
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
Methods
Fraction Interpretation

Light
• New organic matter
• Not much decomposition

Middle
• More stable, broken
down organic

Heavy
• Mineral, silt/sand
(Glazer, 1995)
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 g/ml
1.65
2.4
1.85
2.65
2.0
>2.65
(Sollins, 2006)
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)
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)
Results
Fraction Mass (g soil)
Fraction Dry Mass
•Fractions
similar in mass
20
15
Native
10
Pasture
Plantation Pine
5
0
1.65
1.85
2
2.4
Density Fraction (g/ml)
2.65
>2.65
•1.65, 2.4, 2.65
showed greatest
variation
•Variation only
due to one
sample
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
Results
Total Soil C
Carbon
Least
C mass (grams)
6
•Pasture
Nitrogen
5
4
Native
3
Pasture
2
Plantation Pine
1
•Native
0
Total
•Pasture
•Native
Total Soil N
•Plantation
•Plantation
0.35
N mass (grams)
Most
Least
Most
0.3
0.25
Native
0.2
Pasture
0.15
Plantation Pine
0.1
0.05
0
Total
Results
Fraction Carbon

3
Carbon (g)
2.5
2
Similar for
most fractions
Native
1.5
Pasture
Plantation Pine
1
0.5
0
1.65
1.85
2
2.4
2.65 >2.65
Density Fraction (g/ml)

Major
difference in
the 2.4
fraction
Discussion
Carbon

Native
• 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
Results
Fraction Nitrogen

Nitrogen (g)
0.2
0.15
Similar
across
fractions
Native
0.1
Pasture
Plantation Pine
0.05
0
1.65
1.85
2
2.4
2.65
Density Fraction (g/ml)
>2.65

Major
difference in
2.4 fraction
Discussion
Nitrogen

Native
• 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
Results
C:N value (g C:g N)
Soil C:N
30
25
20
Native
15
Pasture
10
Plantation Pine
5
0
1.65
1.85
2
2.4
2.65
>2.65
Fraction Density (g/ml)


Native highest C:N
Plantation next highest C:N except in 2.4, >2.65
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
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
Fraction Carbon
Fraction Nitrogen
3
20
0.2
15
Native
10
Pasture
Plantation Pine
5
2
Native
1.5
Pasture
Plantation Pine
1
Nitrogen (g)
2.5
Carbon (g)
Fraction Mass (g soil)
Fraction Dry Mass
0.15
Native
0.1
Pasture
Plantation Pine
0.05
0.5
0
0
0
1.65
1.85
2
2.4
Density Fraction (g/ml)
2.65
>2.65
1.65 1.85
2
2.4
2.65 >2.65
Density Fraction (g/ml)
1.65
1.85
2
2.4
2.65
Density Fraction (g/ml)
>2.65
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
Future Research

Deeper Samples Analyzed
• Tree roots may run deeper than grass
• Results in loss of organic matter
when removed
References



P.N. Beets, G.R. Oliver, P.W. Clinton. 2002. Soil
carbon protection in podocarp/hardwood forest,
and effects of conversion to pasture and exotic
pin forest. Environmental Pollution 116: S63S73.
L.A. Schipper, W.T. Baisden, R.L. Parfitt, C. Ross,
F.F. Claydon, G. Arnold. 2007. Large losses of
soil C and N from soil profiles under pasture in
New Zealand during the past 20 years. Global
Change Biology 13: 1138-1144.
R.L. Parfitt, N.A. Scott, D.J. Ross, G.J. Salt, K.R.
Tate. 2003. 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: 203221