Greenhouse gas emissions during plantation stage of

Environ Sci Pollut Res DOI 10.1007/s11356-016-8270-0

RESEARCH ARTICLE

Greenhouse gas emissions during plantation stage of palm oil-based biofuel production addressing different land conversion scenarios in Malaysia Faradiella Mohd Kusin 1,2 & Nurul Izzati Mat Akhir 1 & Ferdaus Mohamat-Yusuff 1,2 & Muhamad Awang 3

Received: 4 March 2016 / Accepted: 13 December 2016 # Springer-Verlag Berlin Heidelberg 2016

Abstract The environmental impacts with regard to agro-based biofuel production have been associated with the impact of greenhouse gas (GHG) emissions. In this study, field GHG emissions during plantation stage of palm oil-based biofuel production associated with land use changes for oil palm plantation development have been evaluated. Three different sites of different land use changes prior to oil palm plantation were chosen; converted land-use (large and small-scales) and logged-over forest. Field sampling for determination of soil N-mineralisation and soil organic carbon (SOC) was undertaken at the sites according to the age of palm, i.e. 21 years (mature oil palms). The field data were incorporated into the estimation of nitrous oxide (N2O) and the resulting CO2-eq emissions as well as for estimation of carbon stock changes. Irrespective of the land conversion scenarios, the nitrous oxide emissions were found in the range of 6.47–7.78 kg N2O-N/ha resulting in 498–590 kg CO2-eq/ha. On the other hand, the conversion of tropical forest into oil palm plantation has resulted in relatively higher GHG emissions (i.e. four times higher and carbon stock reduction by >50%) compared to converted land use (converted rubber plantation) for oil palm development. The conversion from previously rubber plantation into oil palm

Responsible editor: Philippe Garrigues * Faradiella Mohd Kusin [email protected]

1

Department of Environmental Sciences, Faculty of Environmental Studies, Universiti Putra Malaysia UPM, 43400 Serdang, Malaysia

2

Environmental Forensics Research Centre, Faculty of Environmental Studies, Universiti Putra Malaysia UPM, 43400 Serdang, Malaysia

3

SEGi University, Kota Damansara, 47810 Petaling Jaya, Selangor, Malaysia

plantation would increase the carbon savings (20% in increase) thus sustaining the environmental benefits from the palm oilbased biofuel production. Keywords Oil palm . Carbon stocks . Greenhouse gases . Nitrous oxide . Soil organic carbon, biofuel

Introduction The environmental aspect and impact associated with the process of biofuel production to support the sustainability of agro-based energy industries have become the interest of many relevant sectors. Biofuel production from palm oil has been promoted and initiated in Malaysia since a few years back so as to sustain energy production using alternative source of biofuel and to reduce the dependency on fossil fuel. Environmental impacts in terms of energy balance and greenhouse gas (GHG) balance would be of great concern when addressing this issue for sustainability in palm oil-based biofuel production (Siangjaeo et al. 2011; Hansen et al. 2014). However, the increased demand for palm oil-based biofuel has promoted the changes in land use. Land use changes may affect the carbon content in soil (often regarded as the carbon stocks), which is released into the atmosphere thereby contributing to the GHG emissions (Siangjaeo et al. 2011; Castanheira et al. 2014). Whilst it has been found that some land use conversions for oil palm plantation development have resulted in carbon savings (e.g. Brinkmann Consultancy 2009), some studies have also highlighted the negative effect of transforming the forest and peatlands into oil palm plantations, i.e. the associated carbon debt (e.g. Fargione et al. 2008; Danielsen et al. 2008). Because it has been known, that globally the oil palm area expansion is to a great extent influenced by the carbon stock changes due to changes in land use, site- and country-specific investigation would help in

Environ Sci Pollut Res

determining potential for future oil palm plantation development especially with regard to alternative source for biofuel. Palm oil production chain includes several important elements, i.e. system boundaries in typical life cycle inventory, which have been discussed in many life cycle assessments for oil palm-related studies (e.g. Henson 2004; Schmidt 2007; Siangjaeo et al. 2011; Castanheira et al. 2014). Generally, it is known that land use changes (often related to carbon stock changes), oil palm plantation stage and palm oil extraction phases significantly contribute to the emissions of GHGs over the life cycle of palm oil production. The GHG emissions from palm oil production have generally been categorised as the emissions arising from the operations during oil palm growing and fresh fruit bunch (FFB) processing and the emissions arising from carbon stock changes (i.e. during the development of new plantation and during the operations of plantations (Brinkmann Consultancy 2009; Klaarenbeeksingel 2009). The focus of this study is on the emissions during the plantation stage of palm oil production with associated land conversion scenarios for oil palm plantation development. Castanheira et al. (2014) stated that contribution of Nfertilisers is among the main input. In oil palm plantation, the inputs of nitrogen come from synthetic fertilisers and crop residues (IPCC 2000). The direct N emissions include contribution from other elements such as from decomposition of organic matter residues returned to soils, N-mineralisation (Schmidt 2010; Yuan et al. 2016). Additionally, the oil palms may also need supplementary inputs of nitrogen from application of EFB and treated POME apart from addition of phosphate and potassium inputs (Castanheira et al. 2014). These elements contribute significantly to the release primarily of N 2 O alongside CO 2 and CH 4 (Kim and Dale 2008; Inselsbacher et al. 2011). Therefore, in this study the soil Nmineralisation from decomposition of soil organic matter were determined from field data. Field experiment data would provide more reliable evaluation so as for the verification of specific emissions from the reported data. Quantification of Nmineralised in soil organic matter has not been widely investigated for oil palm plantation especially in Malaysian cases (Hansen et al. 2014). In fact, this fraction of N (i.e. the soluble N) has significant contribution to the overall N-related emissions (Schmidt 2010). Additionally, the soil organic carbon (SOC) content was also determined to relate the amount of carbon stocks and land use changes in oil palm plantations of different land conversion scenarios. It is generally known that among the factors that contribute to the increase of nitrous oxide include fertilised soil in agroindustrialisation (Hewitta et al. 2009; Vandermeer et al. 2009; Akhir et al. 2014). Application of inorganic N-fertilisers can contribute to the effect of GHGs through increasing emissions of N2O, CO2 and CH4 from soil (Treseder 2008; Inselsbacher et al. 2011; Akhir et al. 2015; Kusin et al. 2016). Siangjaeo et al. (2011) also found that application of nitrogen fertiliser is

the main source of N2O emission, which is among the major GHGs during plantation stage. N2O can be emitted as a result of nitrification and denitrification processes in natural ecosystems (Giltrap et al. 2014). Therefore, increase in N-fertiliser in soil may directly enhance N2O emission because N2O is produced naturally in soils through the process of nitrification and denitrification (IPCC 2006). It has been found that soil microbial processes also have influence on the production and consumption of N2O from soils. The processes are to a certain extent controlled by the soil oxygen content, temperature, mineral N content in organic matter and pH (Mosquera et al. 2007; Yuan et al. 2016). Furthermore, N-fertiliser is typically applied to enhance rapid growth of oil palm through the root respiration and generally this will lead to increasing CO2 emission in the atmosphere.

Materials and methods Study sites The study was conducted at three different locations of oil palm plantation incorporating the changes in land use prior to the plantation development. Sampling of soil was conducted at Kempas Estate (large-scale converted land use), UPM Oil Palm Plantation (small-scale converted land use) and Chepor Estate (logged-over forest) (Fig. 1). Kempas Estate, which is located in Melaka is a converted land previously planted with other crops such as rubber and cocoa. The estate is a highly degraded land that has total area of 1700 ha and is owned exclusively by Sime Darby Sdn Bhd. The UPM Oil Palm Plantation is also a converted land (previously rubber plantation) and a degraded area of 40 ha (19 ha < 5 years; 14 ha between 5 and 20 years; 7 ha > 21 years). The plantation belongs to UPM Holdings Sdn Bhd and is managed by Taman Pertanian Universiti (TPU) for research purposes. Chepor Estate is a logged-over forest of about 982 ha (125 ha < 5 years; 157 ha between 5 and 20 years; 700 ha > 21 years). Within the Chepor Estate, the sampling was performed specifically at Felcra Chepor which is the oldest oil palm plantation (>21 years), at Pulau Cheri plantation (5– 20 years) and Felcra Raban and Stang private plantation (20 years, (2) between 5 and 20 years and (3) < 5 years

Estate from year 1986 to 2012 and was used to evaluate the variation of annual N2O and CO2-eq emissions over the years (Kusin et al. 2015). These data were compared with the data available for Malaysian scenario (Schmidt 2007) to estimate the average amount of N-fertiliser applied in Malaysian oil palm plantation used in this study. Soil sampling For assessing the amount of N-mineralisation in soil and the resulting N2O and CO2-eq emissions during the agricultural stage of oil palm at different ages, data from a particular period was used (field soil sampling between April 2013–April 2014) comparing immature and mature oil palms. The soil sampling was conducted for the three estates according to the age of the oil palms as noted earlier. Soil samples were analysed for nitrogen content and soil organic carbon (and organic matter). The soil sampling was undertaken in the field using schematic triangular method adapted from Tailliez (1971) and with reference to Sierra et al. (2007) and Portela et al. (2009). Each sampling plot consists of a triangle with three neighbouring oil palm trees where the soil samples were collected at four

different points at four different depths (i.e. 10, 30, 50 and 100 cm) within the triangle. One sample from each plot was collected using a stainless steel cutting ring for analysis of bulk density of the prescribed depths. Three samples were collected using a 7-cm-diameter Edelman auger for analysis of organic carbon and the nitrogen and phosphorus contents. For each site, 48 sub-samples were collected and in total 144 samples have been collected. About 20 kg of total soil were collected from each sampling occasion and they were stored in zipped plastic bags and were labelled accordingly. Samples were brought back to the laboratory and were kept cool until analysis. The samples were stored at 4 °C to prevent moisture loss and composition changes as the biological activity slows at low temperature. All the sub-samples collected were composited according to the prescribed depths in the laboratory prior to soil analysis. The soil samples were air dried in the laboratory at room temperature in a dust and fume-free place. Soil aggregates were then pulverised using mortar and pestle to reduce the size of soil particles. The soil samples were then screened through a 0.25-mm sieve. After screening, soil is thoroughly mixed and put in a plastic pot till analysis. Soil samples were


extracted using 0.01 M CaCl2 (Qian and Shoenau 1995; Houba et al. 2000). Ten grams of air-dried soil sample were shaken for 2 hours at 20 °C in 100 mL of CaCl2 solution. Then, the suspension was centrifuged in the supernatant liquid and were analysed for nutrients using Auto-Analyser instrument. The analysis of soil organic carbon was performed using a calibrated TOC Instrument, LECO CR-412. The soil organic matter was extracted from the value of organic carbon assuming 58% of organic carbon in organic matter (Schumacker 2002).

Estimation of greenhouse gas (GHG) emissions Carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) are significant greenhouse gases emitted during agricultural stage of oil palm plantation. The emissions are determined from relevant substances, i.e. the N, P and C over the life cycle of oil palm (Schmidt 2010). The emissions are typically expressed as carbon dioxide equivalents per unit mass of fertiliser product (e.g. g CO2-eq/kg fertiliser) or element (e.g. g CO2-eq/kg N) (Wood and Cowie 2004). In this study, the emissions are expressed in unit kg CO2-eq/ha for ease of comparison.

Nitrous oxide emissions The models from IPCC (2006) were used in this study to estimate the amount of the GHGs released. The direct N2O emission was calculated according to the IPCC model considering peat soil which is relevant in Malaysia and Indonesia (Schmidt 2007). In fact, most Malaysian oil palm plantation soil is composed of peat, and nearly 50% (or higher) of new plantations are developed on peat soils (Henson 2004; Wetlands International 2007; Adon et al. 2012; Hergoualc’h and Verchot 2013). Notwithstanding this, it is known that this would contribute to significant global warming if cultivation on peat soils is not carefully controlled (Schmidt 2010). The equation used for the estimation of N2O emission is as follows (IPCC 2006):

Table 1 Parameters used in N2O estimation

N2 O−N ¼ ½ð FSN þ FON þ FCR þ FSOM Þ x EF1 þ ð FOS x EF2 Þ

Where FSN is the annual amount of synthetic fertiliser N applied to soils (kg N ha−1); FON:is the annual amount of organic N additions applied to soils (kg N ha−1), FCR is the annual amount of N in crop residues (above-ground and belowground) returned to soils (kg N ha−1), FSOM is the annual amount of N in mineral soils that is mineralised, in association with loss of soil C from soil organic matter as a result of changes to land use or management (kg N ha−1), FOS is the annual area of managed/drained organic soils (ha), EF1 is the emission factor for N2O emissions from N inputs (kg N2O-N/kg N input) and EF2 is the emission factor for N2O emissions from drained/ managed organic soils (kg N2O-N/ha-yr). Details of the parameter values used in this study are provided in Table 1.

CO2−equivalent emissions CO2−equivalent (CO2-eq) is estimated through conversion of other gases to equivalent amount of carbon dioxide based on the Global Warming Potential (GWP). Standard ratios are used to convert the various gases into equivalent amounts of CO2 that describes its total potential warming impact relative to CO2 over a set period. The CO2-eq was calculated through N2O emission conversion using the Global Warming Potential of the gas as follows: . . CO2eq ¼ ð FSN x FE1 Þ x 44 28 x GWP N2O 1000 ð2Þ Where FSN is the annual amount of synthetic N-fertiliser applied to soils (kg N yr.−1), FE1is the emission factor for N2O emissions from N inputs (kg N2O–N kg N input−1), (FSN*FE1) is the annual direct N2O–N emissions from N inputs to managed soils (kg N2O–N yr.−1), 44/28 is the conversion of N2O–N emissions to N2O emissions and GWP is the Global Warming Potential of N2O (t CO2−eq). N2O is a GHG with a GWP 298fold higher than that of CO2 (IPCC 2006).

Parameter

Value

Units

FSN

100 (immature); 110–115 (mature)

kg N ha−1

FON FCR FSOM FOS EF1 EF2

ð1Þ

– 266 (immature); 147 (mature) 158–174 1 (peat soil) 0.001 1.2 (oil palm)

Reference

−1

kg N ha kg N ha−1 kg N ha−1 kg N ha−1 – –

Schmidt (2007); This study No manure applied Schmidt (2007) This study Schmidt (2007) IPCC (2006) IPCC (2014)


Carbon stock changes calculation The amount of carbon stocks were calculated according to the IPCC guidelines as given below: CS ¼ SOC þ C veg ¼ ðSOC x F LU x F MG x F I Þ þ ðC BM þ C DOM Þ

ð3Þ

Where CS is the carbon stocks, SOC is the soil organic carbon (t C ha−1), Cveg is the above and belowground vegetation carbon stock (t C ha−1), CBM is the carbon stock in living biomass (above and belowground biomass) (t C ha−1), CDOM is the carbon stock in dead organic matter (t C ha−1), FLU is the factor that reflects the difference in SOC associated with land use, FMG is the factor associated with management practice and FI is the factor associated with different levels of carbon input to soil. Details of the parameters used are provided in Table 2. For the calculation of carbon stock changes and the resulting CO2-eq emissions, the following equations from IPCC were used (Castanheira 2014):

data, lack of coverage of measurements, spatial aggregation and lack of information on specific on-farm practises (IPCC 2006). Therefore, uncertainties estimation was performed to obverse the variation of N2O and CO2-eq emissions when adopting maximum and minimum values for parameters and emission factors (Castanheira et al. 2014). The calculation of field N2O and CO2-eq emissions was based on the IPCC methodology as mentioned earlier for each land conversion scenario and was compared for default, minimum and maximum parameter values and emission factors from other studies and IPCC.

Results and discussion Greenhouse gas (GHG) emissions during agricultural stage of oil palm plantation N2O emission related to N-fertiliser application

Where CO2-eq is the annualised CO2-eq emission from carbon stock change (t CO2-eq t−1 PO), ΔCS is the changes in carbon stocks (t C ha−1), CSR is the carbon stock of the reference (previous) land use (t C ha−1), CSA is the carbon stock of the actual land use (oil palm plantation) (t C ha−1) and P is the palm oil productivity (t PO ha −1).

The variation of N2O emission related to N-fertiliser application from an oil palm plantation has been presented in Kusin et al. (2015) for the case study of Kempas Estate. The amount of N-fertiliser applied (annual average) at the oil palm plantation and the calculated N2O and CO2-eq emissions have been presented. The amount of the applied N-fertiliser was fairly consistent over the years, and only a little variation in N2O emission was observed. The data was also found to be nearly the values reported for Malaysian oil palm plantation, i.e. Schmidt (2007). Therefore, the data from Kempas Estate have been incorporated along with the reported values for Malaysian scenario for determination of the average Nfertiliser application used in this study.

Uncertainties estimation

N2O emission for oil palms of different ages

It is known that uncertainties of direct N2O emissions from managed soils are caused by uncertainties related to the emission factors, natural variability, partitioning fractions, activity

For further analysis of the data, the N2O emissions during the agricultural stage of oil palm plantation were analysed against the age of the oil palms for a particular period, i.e. measured in

CO2−eq ¼ Δ CS 44 = 12 1 = 20 1 = P ¼ ðCSR–CSAÞ 44=12 1=20 1=P

Table 2 Parameters used in carbon stocks calculation

ð4Þ

N-related parameters

Value

Units

Remarks

SOC

a

t C/ha

Soil organic carbon analysis

– – – t C/ha

European Commisson (2010) European Commisson (2010) European Commisson (2010) Brinkmann Consultancy (2009); Morel (2009); Jiwan and Saharjo (2009)

45–66 33–68 1.0 1.22 1.11 35 b

FLU FMG FI Cveg a

Transformed land use

b

Logged-over forest


2013–2014. The oil palms were classified as immature (less than 5 years) and mature (>5 years) after planting. The N2O emission was calculated taking into account the contribution of N-fertiliser applied as mentioned earlier and field determined data for mineralised-N from organic matter decomposition. The amounts of N-mineralised in soil from the three sites (Kempas Estate, UPM Oil Palm Plantation and Chepor Estate) have been determined experimentally. Other parameters that are not determined experimentally were extracted from previous reported values for Malaysian oil palm plantation (Schmidt 2007). Generally, the N addition to soils is the amount of N in soil that is mineralised in association with loss of soil C from soil organic matter (IPCC 2006). Schmidt (2010) found that organic matter residues vary at different stages of oil palm planting. Taking into account the land use changes of the plantations, Kempas Estate is classified as converted land use (large-scale), UPM Oil Palm Plantation (converted land use, small-scale) and Chepor Estate (loggedover forest). N2O and CO2-eq emissions The resulting N2O and CO2-equivalent (CO2-eq) emissions are discussed here. Table 3 shows the resulting amount of N2O and CO2-eq emissions at the three estates. For Kempas Estate (large-scale converted land use), about 160.44– 169.27 kg N/ha of N-mineralised in soil were estimated. This results in N2O emission of between 6.47 and 7.78 kg N2O-N/ha which corresponds to 498.03–584.56 kg CO2-eq/ ha. At UPM Oil Palm Plantation (small-scale converted land

Table 3 Amount of Nmineralised in soil, resulting N2O and CO2-eq emissions for different types of land use change

use), N-mineralised were found in the range of 165.80– 167.09 kg N/ha which corresponds to 6.49–7.85 kg N2ON/ha and between 499.35 and 589.68 kg CO 2 -eq/ha. Whilst at Chepor Estate (logged-over forest converted into oil palm plantation), the N-mineralised in soil were found between 158.14 and 173.64 kg N/ha which corresponds to 6.58–7.75 kg N2O-N/ha and 506.89–582.40 kg CO2-eq/ha. Accordingly, about 10.13–12.19 g CO2-eq emission have been emitted per MJ oil palm produced at Kempas Estate, whilst UPM Oil Palm Plantation released about 10.16–10.30–32.52 g CO2-eq/MJ palm, and about 10.31–12.14 g CO 2 -eq/MJ palm were emitted from Chepor Estate. N2O emission in oil palm plantation areas is often associated with the use of N-fertiliser, although contribution from organic matter decomposition cannot be ruled out (Henson 2005; Van Noordwijk et al. 2010; Schmidt 2010). Nfertiliser application may increase N2O emissions by 5–6 times at 200 kg N/ha and by 10–14 times at 270 kg N/ha (Zhang et al. 2014). On the other hand, the contribution of N-fertiliser production to the plantation emission vary between 12% from poultry manure, 36% from synthetic fertiliser (ammonium nitrate and calcium ammonium nitrate), phosphorus and potassium fertiliser production are responsible for less than 10% of the plantation GHG emissions, similarly to fossil fuels (Castanheira et al. 2014). Other studies have also found that direct N2O emissions also increase at high N input rates due to N-fertiliser application (Kim et al. 2013; Rashti et al. 2015). The resulting N2O and CO2-eq emissions are illustrated in Fig. 2 on the same scale for comparison. There was no

Age of palm (year)

21 (mature)

169.27 6.59 522.44 10.32

164.43 6.47 498.03 10.13

167.09 6.56 520.28 10.28

165.80 6.49 499.35 10.16

172.49 6.63

173.64 6.58

525.63 10.38

506.89 10.31


values and emission factors (Fig. 3). The N2O emissions vary between 0.96 and 1.27 kg N2O-N/ha when adopting minimum parameter values, between 17.09 and 23.78 N2O-N/ha when maximum values are used, and between 4.93 and 5.96 N2ON/ha using default values. The N2O emissions of different land conversion scenarios range between 6.47 and 7.78 N2O-N/ha. As a result, the CO2-eq emissions vary between 47.60 and 53.44 kg CO2-eq/ha when using minimum values, and between 848.32 and 1027.02 kg CO2-eq/ha when maximum values are used. Differences between CO2-eq emissions using default, minimum and maximum parameter values are significant (p < 0.05), suggesting that careful consideration must be given when choosing the country- and case-specific coefficients for the estimation of such GHG.

Relationship between N-mineralised in soil and age of plantation to N2O emission The correlation coefficients, r between age of plantation and Nmineralised in soil, and the N2O emission are shown in Table 4. The age of oil palm seems to have inverse correlation with the amount of N2O emission. There are significant correlations of

Fig. 2 N2O emission and CO2-eq emission for (a) large scale CLU, (b) small scale CLU and (c) logged-over forest

apparent difference of N2O emissions per ha plantation between different types of land conversion. However, the amount of N2O emissions were slightly higher for immature oil palms aged 5 years for all types of land use conversion. This can be attributed to several factors such as the requirements for nitrogen at the early stage of oil palm growth (Sawan et al. 2001). Generally, the N content during early stage of oil palm growth is influenced by several elements such as the amount resulting from N-fixation, return of nitrogen in crop residues and decomposition of biomass (Schmidt 2007). Likewise, the resulting CO2-eq emissions follow the same trend as for the N2O emission, i.e. emission is slightly higher during early stage of oil palm development. With regard the uncertainties’ estimation, it can be observed that there is variation of field N2O and CO2-eq emissions when adopting maximum and minimum parameter

Fig. 3 Uncertainties estimation for N2O and CO2-eq emissions for different types of oil palm plantations compared with default, minimum and maximum parameter values and emission factors

Environ Sci Pollut Res Table 4 Correlation coefficients between age of plantation and mineralised-N in soil to N2O emission for Kempas Estate, UPM Oil Palm Plantation and Chepor Estate Kempas Estate

Correlation coefficient, r N2O emission

Age of plantation

−0.772**

N-mineralised in soil

0.905**

UPM Oil Palm Plantation Age of plantation N-mineralised in soil

N2O emission −0.873** 0.463*

Chepor Estate Age of plantation N-mineralised in soil

N2O emission −0.316* 0.400*

**Significant at p < 0.01, *Significant at p < 0.05

N2O emission and the age of oil palm at all sites; Kempas Estate (r = −0.772, p < 0.01), UPM Oil Palm Plantation (r = −0.873, p < 0.01) and Chepor Estate (r = −0.316, p < 0.05). Therefore, mature oil palm development seems to release lower amount of N2O compared to immature palms. The relatively higher N2O emission during the immature stage may be attributed to several factors as explained earlier. Additionally, there are positive significant correlations between N-mineralised in soil and the N2O emission at all sites; Kempas Estate (r = −0.905, p < 0.01), UPM Oil Palm Plantation (r = −0.463, p < 0.05) and Chepor Estate (r = −0.400, p < 0.05), indicating that high N2O emission is also attributed to contribution from N in soil particularly from the decomposition of organic matter returned to soils.

of the carbon stocks was performed for two estates, i.e. UPM Oil Palm Plantation (converted land use from previously rubber plantation) and Chepor Estate (logged-over forest) for comparison. Field analysis of soil organic carbon was undertaken for respective sites as mentioned earlier. These data were incorporated into the estimation of the carbon stocks at the plantation areas and to estimate the carbon stock changes with respect to reference (previous) land use (Germer and Sauerborn 2008; Castanheira et al. 2014). The data for carbon content in above and belowground living biomass were adopted from Brinkmann Consultancy (2009) for average Malaysian oil palm value. The carbon stock changes for the two land use change scenarios are given in Table 5. It is noted that the carbon stocks in converted land use (CLU) are between 87.85 and 110.14 t C/ha, whilst in logged-over forest (LOF) the carbon stocks ranges between 96.09 and 114.10 t C/ha. The estimation of the carbon stock changes indicates −27.14 to −4.85 t C/ha in CLU and 110.90 to 128.90 t C/ha in LOF. This implies that the conversion of the tropical forest into oil palm plantation has resulted in reduced carbon stocks within the area. In other words, the transformation into oil palm plantation from tropical forest losses its carbon content (indicated by the carbon release) often referred to as carbon debts of the plantation. On the other hand, the CLU, i.e. from previously rubber plantation has shown some increase in the carbon stocks. As a result, −0.71 to −3.98 t CO2-eq/ha have been estimated from CLU whilst about 16.27 to 18.91 t CO2-eq/ha have been emitted from the LOF. These correspond to −2.38 to −13.32 g CO2-eq/ MJ palm oil for CLU and 54.42 to 63.25 g CO2-eq/MJ palm

Table 5

Carbon stocks in oil palm plantation Carbon stocks and land use changes Greenhouse gas emissions from land use change are regularly debated, particularly in relation to establishment of new plantations on agricultural land. The emissions are in particular related to changes in aboveground and belowground biomass as well as soil organic matter (Brinkmann Consultancy 2009). Specifically, establishment and operation of a new plantation lead to the removal of originally present aboveground and belowground carbon stocks, e.g. forest, shrub land and cropland etc. On the other hand, a plantation stores carbon through the growth of plants. Carbon stock changes due to land use change scenarios of the studied sites are discussed here. The carbon stock changes were calculated taking into account the carbon content in soil (soil organic carbon) and the carbon content in above and belowground living biomass in reference to previous land use of current oil palm plantation as in Eq. 3. The analysis

Carbon stock changes due to land use change scenarios

Age of palm (year)

21 (mature)

87.85

110.14

−4.85

−27.14

−0.71

−3.98

−2.38

−13.32

96.09

97.11

128.90

127.89

18.91

18.76

63.25

62.75

*Carbon stock of reference (previous) land use; rubber (83 t C/ha), tropical rainforest (225 t C/ha) (Brinkmann Consultancy 2009)


oil for LOF. The results are as illustrated in Fig. 4. Therefore, the conversion of oil palm plantation from tropical forest has contributed to greater amount of CO2 emissions; however, transformation from formerly rubber plantation contributed to CO2 savings, which is of great benefits to the environment. It is worth noting again that generally the CO2-eq emissions from the LOF were relatively higher than the CLU. Therefore, this probably explains the significance of the different land use change scenarios on the CO2-eq emission during the agricultural stage of oil palm plantation. Based on the carbon stock changes, CLU (from previously rubber plantation into oil palm plantation) potentially acts as carbons sinks; moreover, it also assigns a positive enhancement in GHG balance. Even though common expansion of Malaysian oil palms resulted from the conversion of LOF, but these scenarios contributed to the unbalance GHG situation. Therefore, proper management on the land use changes have to be implemented as to increase the yield of palm oil production and also to reduce the expansion of oil palm plantation in LOF. Comparison of field data and resulting N2O and CO2-eq emissions for oil palm plantation with other reported values The results obtained from this study were compared to those of the reported values for Malaysian oil palm plantation and elsewhere (Table 6). The N-mineralised from decomposition

Fig. 4 Emissions from carbon stock changes for converted land use (CLU) and logged-over forest (LOF) (a) t CO2-eq per unit area and (b) kg CO2-eq per MJ palm oil

of organic matter in soil found in this study (158–173 kg N/ha) was close to the reported value for Malaysian oil palm plantation, i.e. 159 kg (Schmidt 2007). The SOC were found lower (49–73 t C/ha) than the values reported in Thailand, 71–116 t C/ha (Siangjaeo et al. 2011) and Colombia, 69 t C/ha (Castanheira 2014). No data were found for Malaysian scenario for SOC. Generally, the N2O emissions found in this study are within the range reported from other studies for oil palm plantation (e.g. Melling et al. 2007; Germer and Sauerborn 2008; Castanheira et al. 2014) and lower than reported by Schmidt (2007). The resulting CO2-eq emissions are much lower than the values reported for oil palm plantation elsewhere (e.g. Germer and Sauerborn 2008; Fargione et al. 2008; Wicke et al. 2008; Agus et al. 2010). The carbon stock changes for converted land use from previously rubber plantation (−3.98 to −0.71 t CO2-eq/ha) were found within the range of values reported elsewhere suggesting the increase of carbon stocks from such land conversion into oil palm plantation. However, this is in contrast to Hansen et al. (2014) that found positive carbon stock changes from rubber to oil palm land conversion for Malaysian scenario. The study suggested that there are multiple emissions that also need to be considered despite changes in land use for such case, for instance the emissions that are released during the production of rubber elsewhere. On the other hand, conversion of forest into oil palm plantation has resulted in GHG emissions (16.27–18.91 t CO2-eq/

Schmidt (2007)

b

c

88–110 96–114 −27–(−5) c 110–129

b

c

49–70 56–73

b

d

c

b

a

Brinkmann Consultancy (2009)

Brinkmann Consultancy (2009)

−31–(−16) 52–245

−7.66 1.70–25

c

b

171

a

1500–2000

a

Hansen et al. (2014)

110 415

33 126

c

b

c

b

a

4.5–14.5

30

140

Castanheira et al. (2014)

Melling et al. (2007)

−12–(−19)

b

96–118

71–116

Siangjaeo et al. (2011)

1.2

a

27,000–40,000

129

69

−51 391 c

b

Castanheira et al. *Wicke et al. (2014) (2008)

54,300

*aMurayama and *Agus et al. Bakar (1996) (2010)

N-related emissions during agricultural stage of palm oil production

Logged-over forest

Transformed land use (including rubber plantation, grassland, cassava and other cropland conversion into oil palm plantation)

Malaysian scenario

*Adapted from Page et al. (2011)

c

b

−3.98–(−0.71) 18.91–16.27 (g CO2-eq/MJ) b−13–(−2) c 54–63

Soil organic carbon (t C/ha) Carbon stocks (t C/ha) Carbon stock changes (t C/ha) (t CO2-eq/ha)

N-fertiliser 108–135 100–106 (kg N/ha) N-mineralised 158–174 159 (kgN/ha) b 19–24.5 N2O emission 6.47–7.78 (kg N2O-N/ha) c6.58–7.75 b 498–590 CO2-eq (kg CO2-eq/ha) c507–582 Emissions related to carbon stock changes a This This study Schmidt (2007)

a

a

−85 3300 c

b

Hassan et al. (2011)

33,000

4.1

Germer and Sauerborn (2008)

Melling et al. (2005)

55,000

*Fargione et al. (2008)

1 248 c

b

Silalertruksa and Harsono et al. Gheewala (2012) (2012)

566

a

42,700

53–150

−23.3–14.9 c

Wei et al. (2014)

19,200

*Wicke et al. *Koh et al. (2008) (2011)

Comparison of field data and resulting parameter values for N-related emissions and emissions related to carbon stock changes for oil palm plantation with other reported values

N-related emissions This study

d

Table 6



ha), the values of within the range reported for Malaysian oil palm. The amount of CO2-eq emission/MJ palm oil were found at the rate below the EU-RED criteria of 55 g CO2eq/MJ (European Parliament 2009) for rubber to oil palm land conversion, but slightly higher from tropical forest conversion. Generally, the emissions of CO2-eq found in this study from tropical forest conversion were four times higher than the converted land use from rubber to oil palm plantation.

Conclusions The results from this study have highlighted the contribution of GHG emissions from oil palm plantation of different category of age and with associated land use changes. The findings could be of useful contribution to site-specific cases of GHG emissions with regard to oil palm plantation development for biofuel production. Note that however, the focus of this study was solely on the plantation (agricultural) stage of the palm development over its life cycle. Field experiments were conducted wherever possible to help strengthen the findings on GHG emissions and the carbon stock changes at respective sites. It was found that the N2O emissions were within the range reported from other studies for oil palm plantation whilst CO2-eq emissions were generally lower than other reported studies. Additionally, it was found that the conversion of tropical forest into palm plantation has resulted in relatively higher GHG emissions (four times higher) compared to converted land use for oil palm development. In contrast, the conversion from previously rubber into oil palm plantation has increased the plantation carbon stocks by about 20%. The conversion of tropical forest into oil palm plantation has contributed to relatively significant GHG emissions, i.e. carbon stock reduction by more than 50%. Additionally, the N and P-related emissions were found greater for the loggedover forest compared to the converted land use. Therefore, in support of sustainable biofuel production from such a developing country, future development may need to incorporate the type of land use changes prior to plantation development.

Acknowledgments Funded from the Long-term Research Grant Scheme (LRGS) project number LRGS/6375401, Ministry of Higher Education (MOHE), Malaysia is greatly acknowledged The authors also wish to thank the Universiti Putra Malaysia for the support through Graduate Research Fellowship scheme.

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