Journal of Soil and Water Conservation 63 (4): 2008 (in press), 250-257

Comparing and predicting soil carbon quantities under different land use systems on the Red Ferrosol soils of Southeast Queensland

Tek Narayan Maraseni, Nicole J. Mathers, Ben Harms, Geoff Cockfield, Armando Apan and Jerry Maroulis

Tek Narayan Maraseni

Research Fellow, Australian Centre for Sustainable Catchments (ACSC) University of Southern Queensland (USQ), Toowoomba, Qld 4350, Australia,

email: maraseni@usq.edu.au, Phone +61-7-46312995

Nicole J. Mathers Research Fellow, CRC for Greenhouse Accounting,

GPO Box 475, Canberra, ACT 2601, Australia.

Ben Harms Department of Natural Resources and Mines,

80 Meiers Rd, Indooroopilly, Qld 4068, Australia

Geoff Cockfield

Deputy Dean, Faculty of Business, and Australian Centre for Sustainable Catchments

USQ, Toowoomba, Qld 4350, Australia

Armando Apan Associate Professor, Australian Centre for Sustainable Catchment & Faculty of Engineering and

Surveying, USQ, Toowoomba, Qld 4350, Australia.

Jerry Maroulis Deputy Director, Australian Centre for Sustainable Catchments,

USQ, Toowoomba, Qld 4350, Australia

Abstract

Conversion of forested lands to agriculture, including cultivation and pasture has been linked

to land degradation, including soil compaction, reduced soil fertility and increased salinity

hazard. The Queensland Government is currently providing incentives for landholders to

plant ex-pasture and cropping areas with hardwood plantations. However, there are issues and

uncertainties regarding the economic viability of these land use conversions. Carbon credits

resulting from additional carbon (C) sequestration achieved in the plantations are now

recognised under the Kyoto Protocol, but the nature of the carbon trading scheme that will

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apply is still unclear, as Australia has not ratified the Protocol. This study compared the total

soil C under native scrub (subtropical dry vine forest), grazed pasture, cultivation and spotted

gum (Corymbia citriodora subspecies variegata) forest on the Red Ferrosol soils of the

Kingaroy region in southeast Queensland (SEQ). We have demonstrated how a timeline of

land use change might be useful to predict the soil C trends efficiently and effectively.

Cumulative soil C (including surface litter and particulate organic matter) to 1.2 t m-2 dry soil

ranged from 72 t ha-1 at the cultivated site to 281 t ha-1 under the mature spotted gum forest.

The estimated annual rates of soil C loss under cultivation in last 55 years (1950-2005) was

2.1% and the estimated annual rate of soil C gain in pasture in last 23 years (1983-2005) was

1.1%. The annual rate of soil C gain under spotted gum (in 50 years) was estimated to be

1.4%. Therefore there is considerable potential for spotted gum plantations to sequester soil C

when planted on ex-agricultural land in SEQ.

Key words: Red Ferrosol, land use change, dry land farming, inland Queensland, carbon

sequestration, carbon credits

1. Introduction

Land use change from forest to non-forest use is a major environmental issue around the

world. Land clearing accelerated in the second half of the twentieth century under a

government-sponsored development scheme in Queensland, where cheap land and low-

interest loans were offered with the conditions that land holders improve the land by clearing

(Fensham and Fairfax, 2003). The cleared land was predominantly used for the grazing of

stock. However, in certain areas with favourable climate and topographic factors (such as the

Inland Burnett region of southeast Queensland), much of the cleared land was used for crop

production. Increasing costs of production due to increased input costs and decreasing

commodity prices, especially of the major cereals, created pressure for farmers economically

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(Zammit et al., 2001). This caused a shift in land use around the 1980s from cultivation to

grazed pasture in unproductive cropping land. Recently, due to increased environmental

concerns focussing on land degradation and the risk of dryland salinity, the Queensland

Government has encouraged farmers to plant hardwood plantations on the degraded ex-

cultivated and pasture areas (Lee, 2005; Brown, 2002; DPI&F, 2000; DPI&F and DNR,

1999). Since C is payable in the national and international markets it would be worthwhile to

consider C sequestration potential of different land use systems while making their

comparison.

Spotted gum is becoming synonymous with hardwood plantations in southeast Queensland

(SEQ). There are several reasons for this. Firstly, in recent years, large areas of SEQ have

become World Heritage listed or National Parks, which has diminished the supply of spotted

gum, but its demand is increasing by 2-3% every year (DPI&F and DNR, 1999). Secondly,

although the full rotation data is not available, the early age performance of spotted gum is

quite encouraging (Huth et al., 2004). Thirdly, preliminary results of the genetic

improvement program are promising, as the seedlings are given vegetative propagative

capacity, frost tolerance and Ramularia shoot blight resistance (Lee, 2005). Finally, spotted

gum is highly valued for its durability, hardness and pale colour (Huth et al., 2004). The

Queensland Government, through the SEQ Regional Forest Agreement (SEQRFA) program,

has already approved a $30 million investment plan to increase the hardwood plantation area

in SEQ (DPI&F, 2004). However, the long-term economic viability of the plan in low rainfall

areas is still a cause for concern (Venn, 2005).

In inland Queensland, mean monthly rainfall is always lower than mean monthly evaporation

(Mills and Schmidt, 2000); therefore, soil moisture is the major limiting factor for non-

irrigated crops. Spotted gum plantations could be a viable competitive land use in these areas

if C sequestration is considered, particularly as the Red Ferrosol soils are the main target area

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of the SEQRFA program for plantation establishment. The objectives of this study were: (a)

to compare soil C stocks under different land use systems and (b) to predict the long-term

changes in soil C under different land uses in the Red Ferrosols of SEQ. In particular, we are

interested in the long term soil C sequestration potential of Spotted Gum plantation that were

established in 2001 under the SEQRFA program. Since there was no alternative, mature

spotted gum forest was studied for the proxy value of soil C for the recently established

spotted gum plantation.

2. Methods

2.1 Study Sites

The three sites used in this study were Marshall and Raibe’s properties in Tabingaa, and

Perrett’s property near Kingaroy (26° 35’S, 151° 50’E) in the southern Inland Burnett region

of southeast Queensland. The soil at each site is classified as a Red Ferrosol according to the

Australian Soil Classification of Isbell (2002), or a Tropeptic Eutrustox (i.e. Oxisol) in the

USDA Soil Taxonomy (Soil Survey Staff, 2003). Kingaroy is situated approximately 215 km

northwest of Brisbane and some 130 km inland from the coast. Elevation at Kingaroy is 441

m above sea level. The climate is classified as subtropical, with long summers and mild

winters. Annual rainfall varies from 339 to 1430 mm, with an average of 781 mm, and is

summer-dominant with about 70% falling between October and March. Frosts also occur

during winter, with low-lying areas having the highest number of, and severest, frosts. June,

July and August are the coldest months and on average Kingaroy has 24 heavy and 22 light

frosts each year. Occasional frosts can also occur in May and September. Kingaroy does not

have the high summer temperatures of many other regions in Queensland with December and

January - the hottest months – averaging only 10 days between them over 32°C and usually

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only one day over 38°C. The yearly average maximum temperature is 24.7°C, while the

yearly average minimum is 11.4°C.

Four land use systems were studied; native scrub and grazed pasture at Marshall’s, peanut

(Arachis hypogaea)-maize (Zea mays) cultivation at Raibe’s and mature spotted gum forest at

Perrett’s. Marshall’s was cultivated to peanut-sorghum-maize until 1983 and then became

grazed pasture, however, there are also pockets of remnant native scrub. Raibe’s has been

cultivated with a peanut-maize rotation since 1950. Perrett’s was planted with native spotted

gum approximately 50 years ago on land previously used as pasture. Land use changes at the

study sites are illustrated in Figure 1. Spotted gum plantations have been established as a

SEQRFA program on Marshall’s property in 2001, and the potential soil C sequestration of

these plantations is investigated in this study.

2.2 Soil sampling

The soil samples were taken using a 50 mm soil coring tube driven by a hydraulically

operated soil rig. However, in the native scrub a hand auger was used because the vegetation

was too dense to access with the soil rig. The soil sampling design was based on McKenzie et

al. (2000). Each plot was divided into four quadrats and within each quadrat a sampling

point was randomly located. At each sampling point, one core was taken to 110 cm soil

depth, then four adjacent cores were taken to 30 cm (Figure 2). Each main core was divided

into 0-5, 5-10, 10-20, 20-30, 30-50, 50-70, 70-90 and 90-110 cm depths and bagged in the

field. The smaller cores were divided into 0-5, 5-10, 10-20, and 20-30 cm depths and bulked

with the main core samples. All soil samples were then taken back to the laboratory for

further analysis.

2.3 Surface litter and particulate organic matter sampling

In order to sample surface litter and mulch, a 5 m radius plot was marked from the central

point of the 25 m × 25 m soil plot. At three points within the plot, where litter was ranked

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light, medium or heavy, two quadrats of 50 cm × 50 cm were selected randomly and the litter

collected in paper bags. The area of each litter type was also estimated. Surface litter was

collected and weighed in the field using a calibrated spring balance and bucket. The fresh

weight of surface litter per ha was calculated as follows:

Fresh weight (kg ha-1) = ∑ (Ai × Wi × 20,000)……………………………...1

where ‘A’ is the fraction of area (if 50% then use 0.5) and ‘W’ is fresh weight of surface litter

(kg) of two quadrats from a given surface litter type (i). All litter materials were again

weighed in the laboratory, both fresh and oven-dried at 65°C.

In some areas, particularly the native scrub and mature spotted gum forest, partially

decomposed litter was discovered between the surface litter layer and the soil and termed

particulate organic matter (POM). The same procedure used to sample surface litter was also

used for the POM samples.

2.4 Chemical analysis

Soil materials were air-dried and then sieved using a 2-mm sieve. Coarse material (stones

and roots) was separated and their mass recorded. Representative sub-samples of the soil and

litter were fine-ground for soil C analysis.

Total C of soil, litter and POM samples were determined using an Isoprime isotope ratio mass

spectrometer coupled to a Eurovector elemental analyser (Isoprime-EuroEA 3000) with 10%

replication. Samples containing approximately 50 μg N were weighed into 8 × 5 mm tin (Sn)

capsules and analysed against a known set of standards.

2.5 Calculation of soil C stocks

The amount of soil organic carbon (from < 2mm soil particles) was calculated as follows:

SOC = B × C × D………………………………….........................................2

where SOC is soil organic carbon, B is the bulk density of soil (kg m-3), C is the soil C

concentration (g kg-1 soil) and D is the soil depth in metres.

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However, because there were differences in bulk density between land-uses, soil C

comparisons based on cumulative depth may be misleading. If soil C stocks are given in t ha-

1 to a certain depth across different land uses, then any apparent increase in soil C in more

compacted soil (high bulk density soil) could be due to the greater mass of soil sampled

(Murty et al., 2002). If results are expressed as a percentage basis, an opposite bias could be

encountered (Murty et al., 2002). For accuracy in comparing land use effects on soil C, all

calculations are referred to a fixed dry mass of soil per unit ground area as recommended by

Gifford and Roderick (2003). As an alternative to the standard depth of 30 cm, soil C in the

top 0.4 t dry soil m-2 is adopted. As an alternative to the standard 1 m soil depth, the top 1.2 t

m-2 of dry soil is suggested. Soil C to 0.4 t m-2 and 1.2 t m-2 was calculated from the

cumulative soil C and soil mass relationships using polynomial equations (R2 > 0.999) and

graph interpolation.

2.6 Estimation of long term soil C trend

The soil C content under the native scrub was assumed to have been at equilibrium since

1950. The trendline for soil C under cultivation since 1950 was developed from current soil C

contents of the native scrub and cultivation. Using the cultivation trendline, soil C content in

the pasture for 1983 was estimated (Figure 4). This value and the measured soil C content for

2005 under pasture was used to develop a soil C trendline for pasture, which in turn was used

to estimate the soil C content of the spotted gum plantation in 2001 when it was established.

The soil C content of the mature spotted gum forest was assumed to be the soil C content of

the plantation at 50 years of age. The soil C content of the mature spotted gum forest and the

estimated soil C content of the plantation in 2001 (from the trendline of pasture) were used to

develop the long-term soil C predictions for spotted gum plantations. Carbon dioxide

emission rates after land use change from native scrub to cultivation could initially be high,

declining over time (Dalal and Carter 2000). Conversely, land use change from cultivation

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and pasture to plantation can be expected to increase soil C content, slowly (even decrease

very early years) at first and then at a faster rate as time progresses (Paul et al., 2003a). These

facts were considered while developing the trendlines.

3. Results and Discussion

3.1 Soil C stocks

The soil C concentration decreased with depth in all land-uses (Figure 3). The mature spotted

gum forest had the greatest soil C concentration down to 50 cm depth followed by the native

scrub. The cultivation had the lowest soil C concentration at all soil depths. When soil C for

the different land uses is compared using equivalent mass units (1.2 t dry soil m-2) the mature

spotted gum forest had the greatest soil C content (267 t ha-1), compared to 178, 145 and 72 (t

ha-1) for the native scrub, pasture and spotted gum forest, respectively (Table 1).

Many national and international soil C studies have compared the soil C changes due to land-

use change up to 30 cm depth (Murty et al., 2002; Paul et al., 2002; Paul et al., 2003a).

However, a special report of the Intergovernmental Panel on Climate Change (IPCC, 2000)

estimated the total land and total soil C (up to one metre depth) of all prominent land-use

systems in the world. The global average soil C to 1 m soil depth for cultivated areas is 80 t

ha-1 (IPCC, 2000), whereas the cultivated area in this study had the slightly lower value of 72

t ha-1 to approximately 1 m depth. The estimated soil C content at the pasture site of 74 t ha-1

(to 30 cm depth or 0.4 t dry soil m-2) is similar to the average of 68 t ha-1 for 24 pasture sites

across SEQ (Paul et al., 2003a).

The soil C content up to 1 m depth in tropical forests, temperate forests and boreal forests

were 123, 96 and 343 t ha-1, respectively (IPCC, 2000). The soil C content of the mature

spotted gum forest in our study was 267 t ha-1 although it was expected to be somewhere in

between the values for tropical and temperate forests. In fact it was much greater than both

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these regions and unexpectedly closer to the world’s richest ecosystem, the boreal forests.

Saffigna et al. (2000) quote similar concentrations of soil C for a native scrub site in the same

region of south east Queensland. This indicates that remarkably high levels of soil C are

achievable in these ecosystems. Tropical savannas and temperate grasslands up to 1 m depth

had 117 and 236 t C ha-1, respectively (IPCC, 2000). Soil C under the pasture area of this

study was in between these two figures at 145 t C ha-1.

3.2 Surface litter and particulate organic matter (POM)

Surface litter was present in all land uses except the cultivation (Table 2). The greatest

amount of surface litter was found in the native scrub (119.2 t ha-1 dry weight, DW), which

was 7.3 times greater than the mature spotted gum forest (16.4 t ha-1 DW). POM in the

mature spotted gum forest (30.1 t ha-1 DW) was approximately 24% less than that for POM in

the native scrub (39.5 t ha-1 DW). The C content in all surface litter and POM components

was less than 50% (Table 2).

The greatest C content in POM was found in the mature spotted gum forest with 8.12 t C ha-1

(Table 2), almost double that in the native scrub (4.18 t C ha-1). However, the greatest surface

litter C content was found in the native scrub (46.5 t C ha-1), which is more than seven times

that in the mature spotted gum forest (6.21 t C ha-1).

When total carbon (including soil, POM and surface litter) is considered, the greatest C

content was found in the mature spotted gum forest (281.3 t ha-1) followed by the native

scrub with 228.6 t ha-1 (Table 3). The cultivated area had the lowest total C content (72 t ha-

1), most probably a result of removal of the crop biomass at harvest, lower soil C contents, a

distinct lack of surface litter and POM and no fallow or plant residues remaining between

crop rotations.

3.3 Long-term prediction of total soil C stocks

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The initial total soil C under cultivation in 1950 was estimated at 228.6 t ha-1. After

continuous cultivation of peanut and maize for 55 years it was reduced to 72 t ha-1,

decreasing annually at a rate of 2.1% (Figure 4). Similarly, the total soil C of pasture was

estimated at 114.3 t ha-1, when it was established in 1983. After 22 years of continuous

pasture the total soil C content was 146 t ha-1, a net annual increase rate of 1.1%. The total

soil C of the plantation in 2001 was estimated as 139.6 t ha-1, and could reach approximately

280 t ha-1 after 50 years with an annual increasing rate of 1.4%.

The predicted results indicate that total soil C in the pasture and spotted gum plantations will

increasing, while under cultivation soil C will continue to decline (Figure 4). Until the first

rotation is harvested there will not be a large difference in soil C between the pasture and

plantation, but larger differences are expected in the long-term. However, if spotted gum is

planted on previously cultivated land there may be large difference in soil C even in the first

rotation.

The literature on soil C dynamics after afforestation of ex-agricultural land also indicates that

soil C is likely to increase after afforestation of hardwood species (Paul et al., 2002; Paul et

al., 2003a; Saffigna et al., 2004). In fact, the newly established plantations at the research site

are actually a silvipastoral system which includes nitrogen fixing legumes along with exotic

and native grasses species that are planted as an intercrop along with the spotted gum. Since

the accumulation of soil C is greatest when there are N2-fixing species present (Paul et al.,

2002), the prospects for soil C sequestration in the plantations is enhanced. However, with

reference to this study some other factors, which are discussed in implications of the study,

need to be considered.

4. Conclusion

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This study has demonstrated how a timeline of land use change might be useful to predict soil

C trends using a minimum number of land use systems. Comparison of the total soil C

contents and the annual changes in total soil C content under different land uses indicates that

planting spotted gum on ex-cultivated or agricultural land in the Kingaroy area has

considerable potential for sequestering soil C. However, the predicted rate of change in total

soil C should be used cautiously as it applies only to Red Ferrosol soils in the southeast

Queensland environment. Further research would be required before application of this model

to other soil types or climatic regions.

5. Implication of the study

There are several implications of the study. The annual rate of loss of soil C in cultivation

(2.1%) and annual rate of gain of soil C in pasture (1.1%) is very high in the long-run.

However, for the comparison of soil C (for the purpose of carbon credit/benefit) with

currently established plantations the current rate should be applied, that is the annual loss of

1.48% in cultivation and the annual gain of 0.45% in pastureland (Figure 4). As explained in

the text, the mature spotted gum (MSG) was studied for the proxy value of soil C for newly

established spotted gum plantations. New plantations are a silvipastoral, including grasses

and legumes which can enhance soil C. However, before transferring the research benefit

from mature spotted gum to plantation sites we have to consider three things. Firstly, the

MSG forest was planted in pastureland & nobody knows for how long the pasture was there.

Secondly, they have been practicing selective harvesting and the crown cover of MSG is well

maintained all the time. Thirdly, the soil C under the MSG could not accurately reflect the

plantations over 50 years as the agricultural soil is so clapped it would never return to its

original condition. Therefore, for the comparison of plantations with other land uses various

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lower soil C scenarios (10 or 20% lower than the actual rate), rather than the actual rate,

should be considered.

6. Acknowledgements

We would like to thank Neil Halpin (DPI&F) for advise on potential research sites, property

owners for access to the sites, Rene Diocares of Griffith University for IRMS analysis and

Colin Marshall, Mike Bell (DPI&F), Ram Dalal and Phil Moody (both NR&M) for helpful

discussions on the site histories, soils and data. Tarong Energy, University of Southern

Queensland (USQ) and Queensland Department of Natural Resources and Mines are

acknowledged for financial and operational support. The preliminary version of this paper

was presented in the International Workshop on Development of Models and Forest Soil

Surveys for Monitoring of Soil Carbon at Koli Finland, 5-8 April 2006. We would like to

thank the organizer and USQ for traveling and logistic support for presentation of this paper

in the workshop. Our thanks also go to the participants of the workshop for their critical

comments and suggestion.

6. References

Brown, A. J., 2002. "Collaborative Governance Versus Constitutional Politics: Decision Rules for Sustainability from Australia's South East Queensland Forest Agreement." Environmental Science & Policy 5: 19-32.

Dalal, RC, Carter J.O., 2000 Organic matter dynamics and carbon sequestration in Australian tropical soils. In ‘Global climate change and tropical ecosystems’. (Eds R Lal, JM Kimble, BA Stewart) pp. 283-314. (Advances in Soil Science Series. CRC Press: Boca Raton, Florida)

Department of Primary Industries and Fisheries (DPI&F), 2004. The Queensland Forestry Industry: An Overview of the Commercial Growing, Management and Processing of Forest Products in Queensland, Queensland Government, Department of Primary Industries and Fisheries, Queensland, Australia.

Department of Primary Industries and Fisheries (DPI&F), 2000. Investigating in Queensland's Private Plantations, Queensland Government, Department of Primary Industries, Brisbane, Queensland.

Department of Primary Industries and Fisheries and Department of Natural Resources (DPI&F and DNR), 1999. "Moving Towards Hardwood Plantation." Between The Leaves: www.forests.qld.gov.au/educat/btl/hardwood.htm Cited on 21/10/2004, 3p

Fensham, RJ & Fairfax, R.J., 2003. 'Assessing woody vegetation cover change in north-west Australian savanna using aerial photography', International Journal of Lifecycle Assessment, vol. 12, pp. 359-67

12

Gifford, RM & Roderick, M., 2003. 'Soil Carbon Stocks and Bulk Density: Spatial or Cumulative Mass Coordinates as a Basis of Expression?' Global Change Biology, vol. 9, pp. 1507-14.

Huth, J, Lee, D, Lawson, S & Smith, T., 2004. Hardwood Plantation Research Field Tour: Tour of hardwood trials in Wide Bay-Burnett region of Queensland, Queensland Government, Department of Primary Industries and Fisheries.

Intergovernmental Panel on Climate Change (IPCC), 2000. Land use, Land-use Change and Forestry. A Special Report of the Intergovernmental Panel on Climate Change. R. T. Watson, I. R. Noble, B. Bolinet al, Cambridge University Press, Cambridge, UK.

Isbell, R.F., 2002. The Australian Soil Classification, CSIRO Publishing, Collingwood, Victoria Lee, D., 2005. Hybrids: Spearheading Hardwood Plantation Establishment, A Leaflet Distributed in

IUFRO World Forestry Congress, Queensland Government, Department of Primary Industries and Fisheries.

McKenzie N, Ryan P, Fogarty P, Wood J., 2000. Sampling, measurement and analytical protocols carbon estimation in soil, litter and coarse woody debris. National Carbon Accounting System, Technical Report No. 14, Australian Greenhouse Office: Canberra.

Mills, G. and Schmidt, D., 2000. Overview of Cropping in the South Burnett Crops Grown and Climate, Department of Primary Industries and Fisheries, Queensland Government, http://www.dpi.gov.au./fieldcrops, Cited on 11/05/2005 (2000).

Murty, D, Kirschbaum, MUF, McMurtrie, RE & McGilvray, H., 2002. 'Does Conversion of Forest to Agricultural Land Change Soil Carbon and Nitrogen? A Review of the Literature', Global Change Biology, vol. 8, pp. 105-23

Paul, K, Polglase, P & Richards, G.P., 2003a. Sensitivity Analysis of Predicted Change in Soil Carbon Following Afforestation, Ecological Modelling, vol. 164, pp. 137-52.

Paul, K, Polglase, P, Nyakuengama, JG & Khanna, P.K., 2002. Change in Soil Carbon Following Afforestation, Forest Ecology and Management, vol. 168, pp. 241-57.

Paul, KI & Polglase, P.J., 2004. Calibration of the RothC model to Turnover of Soil Carbon Under Eucalypts and Pines, Australian Journal of Soil Research, vol. 42, pp. 883-95.

Saffigna, PG, Moody, PM & Mathers, N.J., 2004. 'Impact of Cropping on the Soil C and N, and the Potential for C Sequestration under the Hardwood Forest Plantations in Subtropical Queensland, Australia', paper presented to ISCO 2004-13th International Soil Conservation Organization Conference-Brisbane, July 2004, Conserving Soil and Water for Society: Sharing Solutions.

Soil Survey Staff, 2003. Keys to Soil Taxonomy. 9th ed. p237-252. USDA, Natural Resources Conservation Service, Washington DC. Available online at http://soils.usda.gov/technical/classification/tax_keys/keysweb.pdf .viewed on 12/2/05

Venn, T. J., 2005. Financial and Economic Performance of Long-rotation Hardwood Plantation Investments in Queensland, Australia. Forest Policy and Economics 7: 437-454.

Zammit, C., Apan, A., Cockfield., G, Brocque., AL & Bouldin., M.R., 2001. Prospects for Regional Sustainability: Land Use Change in the Eastern Darling Downs, 1975-2001

http://www.usq.edu.au/lurc/LandUseChange.pdf cited on 1-11-05, Land Use Study Centre, University of Southern Queensland (2002).

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Pasture to spotted gum in 2001

Cultivation to pasture in 1983

Figure-1: Land-use changes at Kingaroy

Native Scrub

Scrub to cultivation in 1950

Continue scrub

Continue cultivation

Continue pasture

Pasture to spotted gum forest in 1955

Continue spotted gum

Pasture

14

25 m

25 m

Figure 2: Field Soil Sampling Layout

15

0

20

40

60

80

100

120

0.00 2.00 4.00 6.00 8.00 10.00 12.00Total C (%)

Dep

th (c

m)

Pasture Cultivation Native Scrub matute spotted gum

Figure 3: Total C percentage at different depths in the different land use systems at Taabinga, near Kingaroy

16

0

50

100

150

200

250

300

1940 1960 1980 2000 2020 2040 2060

Cum

ulat

ive

soil

carb

on to

1.2

t/m

2 (t/

ha)

Cultivation Pasture Plantation

Figure 4: Long-term prediction of total soil C of various land use systems extrapolated from past trend.

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Table 1: Cumulative soil C under different land uses systems, near Kingaroy, southeast Queensland. Land uses Cumulative Soil C to 0.4 t m-2 (t

ha-1) Cumulative Soil C to 1.2 t m-2 (t

ha-1) Cultivation 38 72 Pasture 74 145 Native Scrub 85 178 Mature Spotted Gum 202 267

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Table 2: Amount of surface litter and particulate organic matter (POM) in different land use types, near Kingaroy, southeast Queensland.

Litter/POM type fresh:dry wt ratio

Fresh wt ha-1 Dry wt

t ha-1 Content types

Sampled DW C (%) t C ha-1

1.06 6.17 5.82 dirt 102.9 11.37 0.51 grass 14.28 38.72 0.24 misc. 5.19 40.68 0.09 twigs 0.61 39.93 0.01 leaf 2.35 38.83 0.04 grass stem 1.63 39.40 0.03 crust 5.14 32.76 0.07 grass rhizome 0.47 38.79 0.01

Pasture surface litter

Total 132.57 1.01 1.07 17.55 16.4 dirt 55.15 36.65 4.19

misc. 2.51 18.05 0.09 grass 0.15 37.61 0.01 gum nuts 1.92 44.22 0.18 bark 9.03 42.11 0.79 twigs 7.42 44.03 0.68 leaf 2.94 45.19 0.28

Mature spotted gum surface

litter

Total 79.12 6.21 1.06 31.95 30.14 dirt 102.88 21.46 4.51

twigs 13.83 42.52 1.20 bark 16.85 43.75 1.51 leaf 5.49 45.36 0.51 gum nuts 3.58 41.25 0.30 grass 0.28 37.17 0.02 insects 0.02 32.74 0.00 stones 4.67 7.94 0.08

Mature spotted gum POM

Total 147.6 8.12 1.03 40.70 39.51 dirt 183.72 10.50 3.98

bark 0.86 31.78 0.06 twigs 0.66 35.89 0.05 roots 0.04 29.64 0.00 leaf 0.95 39.52 0.08 stones 5.35 0.97 0.01

Native scrub POM

Total 191.58 4.18 1.05 125.20 119.24 dirt 15.96 33.44 13.24

leaf 14.67 42.77 15.56 leaf twigs 4.26 42.28 4.47 bark 3.74 38.94 3.61 branch twigs 8.73 42.26 9.15 misc. 0.71 24.48 0.43

Native scrub surface litters

Total 48.07 46.46

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Table 3: Total C content under three land use systems at Taabinga, near Kingaroy, southeast Queensland.

Land use types POM, t C ha-1Surface litter, t C

ha-1 Soil C, t C ha-1Total C, t C

ha-1

Cultivation 0 0 72 72Pasture 0 1.01 145 146Native scrub 4.18 46.46 178 228.6Mature spotted gum 8.12 6.21 267 281.3

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