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Presentation by Dr Susan Orgill to the Riverina branch of the Australian Society of Soil Science at a meeting on 14 March 2014 at Charles Sturt University, Wagga
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Soil carbon under perennial pastures in SE NSW
Susan OrgillResearch Officer – Soil Carbon
Wagga Wagga Agricultural InstitutePhD candidate - CSU
CSU and FFI CRCSupervisors:Dr Jason Condon (CSU)Dr Mark Conyers (DPI)Dr Brian Murphy (OE&H)Dr Richard Greene (ANU)
Research aim and context
• Investigate the role of perennial pastures in maximising organic carbon in soil– Does soil under introduced perennial
pastures accumulate more carbon than native pastures?
– Does parent material influence the capacity of soil to accumulation carbon?
– What is the role of management in accumulating carbon in soil under perennial pastures?
Monaro and Boorowa regions, SE NSW
Monaro basalt
Monaro (and Boorowa) deep granite
Monaro shallow granite
Sampling, analysis and calculations
• Sites sampled to 0.70 m • Sampled according to national
protocols• Samples analysed for chemical
and physical properties
• Carbon units: Total Carbon (LECO); g/100g
C stock (Mg C/ha) = C conc (g/100g) x BD (g/cm3) x depth (cm) x gravel corr factor
Soil C profiles: TC and LC g/100g
Total C (g/100g)
Dep
th (
m)
0
0.2
0.4
0.6
Monaro Basalt
0
0.2
0.4
0.6
Monaro Shallow Granite
0
0.2
0.4
0.6
Monaro Deep Granite
0
0.2
0.4
0.6
0 2 4 6
Boorowa Deep GraniteNativeIntroduced
Labile C (g/100g)
Dep
th (
m)
0
0.2
0.4
0.6
Monaro Basalt
0
0.2
0.4
0.6
Monaro Shallow Granite
0
0.2
0.4
0.6
Monaro Deep Granite
0
0.2
0.4
0.6
0.0 0.5 1.0 1.5
Boorowa Deep GraniteNativeIntroduced
Carbon density (Mg C/ha) Region Parent material Vegetation
0-0.70 (m) s.e.
Monaro Basalt Introduced 160.38 10.8 Basalt Native 156.86 10.1 Basalt Remnant 116.29 unreplicated Deep granite Introduced 77.99 11.4 Deep granite Native 75.00 11.1 Deep granite Remnant 44.58 unreplicated Shallow granite Native 43.29 3.4
Boorowa Deep granite Introduced 52.35 2.8 Deep granite Native 51.25 2.8 Deep granite Remnant 49.24 unreplicated
Soil C stocks (Mg C/ha to 0.70 m)
n.s.
n.s.
n.s.
Pasture comparison: Introduced vs Native Pastures NO difference in these regions
Carbon density (Mg C/ha) Region Parent material Vegetation
0-0.70 (m) s.e.
Monaro Basalt Introduced 160.38 10.8 Basalt Native 156.86 10.1 Basalt Remnant 116.29 unreplicated Deep granite Introduced 77.99 11.4 Deep granite Native 75.00 11.1 Deep granite Remnant 44.58 unreplicated Shallow granite Native 43.29 3.4
Boorowa Deep granite Introduced 52.35 2.8 Deep granite Native 51.25 2.8 Deep granite Remnant 49.24 unreplicated
Soil C stocks (Mg C/ha to 0.70 m)Parent material comparison: Significant difference within region
P<0.05
Basalt soils 159 (11 se)
Deep granite soils 77 (11 se) Shallow granite soils 43 (3 se)
Carbon density (Mg C/ha) Region Parent material Vegetation
0-0.70 (m) s.e.
Monaro Basalt Introduced 160.38 10.8 Basalt Native 156.86 10.1 Basalt Remnant 116.29 unreplicated Deep granite Introduced 77.99 11.4 Deep granite Native 75.00 11.1 Deep granite Remnant 44.58 unreplicated Shallow granite Native 43.29 3.4
Boorowa Deep granite Introduced 52.35 2.8 Deep granite Native 51.25 2.8 Deep granite Remnant 49.24 unreplicated
Soil C stocks (Mg C/ha to 0.70 m)Climate comparison: Significant difference with region/climate
P<0.05Monaro region 76.5 (11 se) Boorowa region 51.8 (3 se)
What is driving the difference with region? Climate and decomposition.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
0
10
20
30
40
50
60
Ave
rage
rai
nfal
l (m
m)
−505
1015202530
Tem
pera
ture
(°C
)
Mean monthly °C max and min● Monaro▲ Boorowa
Mean monthly mmDark MonaroLight Boorowa
Similar potential to grow biomassDifferent decomposition potential
In Monaro region: 1. Strongly summer dominant rainfall 2. Colder and for longer
In Boorowa region:Soil moisture is less variable seasonally and therefore more available for OM decomposition
Evidence: Higher labile C concentrations in deep granite-derived soil from the Monaro region
Key message 1: Parent material, soil depth and climate significantly influence
soil C stock
• Influence supply and decomposition of OM • Parent material (texture, structure and soil depth) influences:
– Soil water and nutrient holding capacity = Ability to supply OM– Clay content and nutrients = Ability to physically and chemically
protect OM
• Climate (rainfall and temperature) influences:– Biomass (OM) supply– Rate of OM decomposition
• Implications– These factors cannot be changed and therefore define the
sequestration potential of a soil type-region
2009
Granite derived soil
40 Mg C/ha 0.30m 2012 47 Mg C/ha
+2.4 t/C/ha/yr from 09-12
And in some cases … just add water…
2009
Basalt derived soil
104 Mg C/ha 0.30m 2012 131 Mg C/ha
+8.8 t/C/ha/yr from 09-12
Explaining the variability within a parent material group
• Assess correlations with C using a multivariate linear model– 52 paddocks– 7 soil chemical traits (TC, TN, labile C, available Colwell
P, extractable S, CEC and pH CaCl2) – Average surface (0 to 0.20 m) data
• Correlation = class + region + errorClass = parent material and vegetation typeError = multivariate normal with mean zero
Correlations between carbon and nutrients under pastures
• C is significantly and positively correlated with:– Total N, Labile C, Extractable S, CEC
10.21-0.29*0.31*-0.080.29*-0.06pH
10.220.49**0.260.210.51**CEC
1-0.090.60**0.31*0.52**Extr S
1-0.060.020.19Col P
10.74**0.85**Labile C
10.80**Total N
1Total C
pH(CaCl2)
CEC(cmolc/kg)
Extr S(mg/kg)
Col P (mg/kg)
LC(g/100g)
TN(g/100g)
TC(g/100g)
Key message 2: Pasture nutrition may increase soil C
• C sequestration is strongly related to soil fertility • We can influence available S and P to maximise biomass
production and therefore OM supply to soil• Nitrogen primarily from legumes• Phosphorus and sulfur are commonly applied as mineral
fertilisers to increase legume production, function and nodulation (thereby N fixation)
• Implications– Maintaining adequate pasture nutrition may substantially
increase soil carbon stocks but this may come at a cost
Influence of grazing management, Boorowa region
• Similar to Chan et al. 2010; n.s.d with grazing management to 0.30m
• Higher C stock under CG 0.70m• Annual stocking rate (DSE) n.s.• All RG sites low-input (i.e. not fertiliser
for >10yrs), therefore may be more related to nutrient management
• Importance of subsoil C sequestration and sampling to depth
� �
� �
No difference 0-0.30m; signif diff 0-0.70m
49.4 (3.5)4.8 (1.3)7.5 (1.3)7.0 (1.3)14.6 (1.3)Native - RG
53.6 (3.9)6.1 (1.4)7.9 (1.4)7.1 (1.4)13.4 (1.4)Native - CG
48.0 (3.5)4.9 (1.3)7.1 (1.3)7.0 (1.3)13.0 (1.3)Introduced - RG
57.8 (3.9)6.7 (1.4)8.7 (1.4)7.7 (1.4)15.7 (1.4)Introduced - CG
0-0.700.20-0.300.10-0.200.05-0.100-0.05
Depth (m)Vegetation
Of the total C stock to 0.70 m, in the 0.30 - 0.70 m soil layer…• Monaro region
– basalt-derived soil 43% – deep and shallow granite-derived soil 28%
• Boorowa region 0.30 - 0.70 m– deep granite-derived soil 33%
• Implications– Restricting to the surface 0.30 m may result in erroneous
conclusions – Opportunities may exist for subsoil C sequestration– Carbon in subsoil may be more permanent
Key message 3: Subsoil C is important
Where to now (for me)…. Making soil sampling and analysis cheaper…
Susan Orgill | Research Officer - Soil CarbonNSW Department of Primary IndustriesWagga Wagga Agricultural Institute M: 0428 424 566 E: [email protected]
• Parent material, soil depth and climate significantly influencedsoil C stock under perennial pastures
• Pasture nutrition may increase soil C (but this may come at a cost)
• Pasture type and grazing management did not increase soil C (in the surface 0.30m)
• Subsoil C is important and should be considered when comparing the influence of land management on soil C
Key messages