Dampak Pemupukan Nitrogen Terhadap Emisi N2O Tanah Pada Perkebunan Sawit di Gambut
THE EFFECT OF NITROGEN FERTILIZATION ON
SOIL N2O EMISSIONS FROM OIL PALM CULTIVATION
ON DEEP PEAT
SATRIA OKTARITA
GRADUATE SCHOOL
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
2014
STATEMENT OF THESIS, SOURCES OF INFORMATION
AND COPYRIGHT*
I hereby certify that this thesis entitled The Effect of Nitrogen Fertilization
on Soil N2O Emissions from Oil Palm Cultivation on Deep Peat is my work under
the supervising committee and never been submitted in any form to any higher
education institution. Materials previously published or written by other person
mentioned in the text and listed in the Bibliography at the end of this thesis.
I hereby bestow the copyright of my papers to the Bogor Agricultural
University.
Bogor, March 2014
Satria Oktarita
ID P052110221
RINGKASAN
SATRIA OKTARITA. Dampak Pemupukan Nitrogen Terhadap Emisi N2O Tanah
Pada Perkebunan Sawit di Gambut Dalam. Dibimbing oleh SYAIFUL ANWAR
dan KRISTELL HERGOUALC’H.
Sektor pertanian berkontribusi 13.5% dari total emisi Gas Rumah Kaca
(GRK) dunia (IPCC 2007). Emisi dari sektor ini umumnya dalam bentuk
dinitrogen oksida (N2O) (46%), metana (CH4) (45%) dan karbon dioksida (CO2)
(9%) (Baumert et al. 2005). N2O termasuk dalam GRK berumur panjang and
memiliki potenti gas rumah kaca (GWP) 300 kali lebih tinggi dibanding CO2.
Konsentrasi N2O pada tahun 2005 adalah sebesar 319 ppb dimana konsentrasi ini
lebih tinggi 18% jika dibanding konsentrasi sebelum masa industrialisasi (IPCC
2007). Sawit merupakan salah satu komoditas yang berkembang sangat pesat di
daerah tropis (Fitzherbert et al. 2008). Malaysia dan Indonesia mulai
mendominasi produksi minyak sawit sejak tahun 1966 (Poku 2002) dan Indonesia
menjadi negara produsen minyak sawit mentah (CPO) terbesar didunia sejak
tahun 2005. Pada tahun 2006 Indonesia memiliki 4.1 juta hektar perkebunan sawit
atau sekitar 31% dari luas total perkebunan sawit diseluruh dunia (Koh dan
Wilcove 2008). Konversi hutan alam menjadi perkebunan sawit berkontribusi
terhadap 10% deforestasi di Indonesia dan Malaysia pada tahun 1990 hingga 2010
(Koh et al. 2011) menyebabkan hilangnya keanekaragaman hayati dan
berkontribusi terhadap perubahan iklim (Murdiyarso et al. 2010, Hergoualc’h dan
Verchot 2011). Disisi lain sawit merupakan salah satu penyumbang pertumbuhan
ekonomi dan sumber bahan bakar alternatif (Sheil et al. 2009).
Gambut diklasifikasikan sebagai lahan marginal karena miskin hara
(Murdiyarso et al. 2010, Sabiham 2010). Penambahan nutrisi tanah misalnya
pupuk untuk meningkatkan hasil pr
oduski dapat meningkatkan oksidasi bahan organik tanah dan meningkatkan
emisi CO2 dan N2O dari tanah (Murdiyarso et al. 2010, Hadi et al. 2001).
Tujuan penelitian adalah untuk (a) mengukur dampak dosis pupuk nitrogen
terhadap emisis N2O tanah (b) mengetahui keterkaitan emisi tanah dengan
variabel lingkungan termasuk kelembaban tanah, suhu, pori tanah terisi air
(WFPS) dan ketersediaan nitrogen.
Selama masa pengukuran 85% flux tanah merupakan flux positif (emisi).
Flux negatif dan rendah ditemukan pada pengukuran yang dilakukan pada kondisi
kering terutama pada tanggal 23 dan 25 Oktober 2012. Peningkatan emisi N2O
terlihat 10 hari setelah pemupukan pada semua perlakuan setelah terjadinya hujan.
Puncak emisi terjadi 19 hari setelah pemupukan namun tidak sepenuhnya
disebabkan oleh aplikasi pupuk.
Hasil penelitian ini menunjukkan hubungan yang signifikan antara N2O
(P=0.05) dengan variabel lingkungan yaitu tinggi muka air, kadar air volumetrik,
WFPS, kadar air gravimetrik namun R2 sangat rendah (R2 =0.02, R2=0.08,
R2=0.02, R2=0.03). Tidak ditemukan hubungan yang nyata antara emisi N2O baik
dengan NH4+ maupun NO3ˉ. Namun, N2O memiliki hubungan yang nyata dengan
rasio NO3ˉ/ NO3ˉ+ NH4+ sebelum atau setelah inkubasi (R2= 0.16 P= 0.02, R2=
0.17 P=0.02).
Emisi N2O yang ditemukan dalam penelitian ini jauh lebih besar jika
dibandingkan dengan literatur dari penelitian terdahulu tentang emisi sawit yang
ditanam di daerah gambut (Melling et al. 2007). Penelitian terdahulu menemukan
emisi gambut tahunan sebesar 1.2 kg N ha-1 tahun-1 dengan kisaran flux antara 0.9
- 58.4 mg N m-2 h-1 pada perkebunan sawit berusia 4 tahun yang dipupuk dengan
nitrogen sebesar 103 kg N ha-1 tahun-1. Penelitian ini menemukan bahwa emisi
N2O masing-masing 18, 10 dan 20 kali lebih besar untuk N0, N1 dan N2. Kajian
ini mendapatkan emisi dengan nilai yang lebih dekat dengan default value IPCC
yaitu sebesar 16 kg N ha-1 tahun-1.
SUMMARY
SATRIA OKTARITA. The Effect of Nitrogen Fertilization on Soil N2O
Emissions from Oil Palm Cultivation on Deep Peat. Supervised by SYAIFUL
ANWAR and KRISTELL HERGOUALC’H.
Agriculture contributes to 13.5% of worldwide greenhouse gases (GHG)
emissions (IPCC 2007). The emissions from this sector are mainly in the form of
nitrous oxide (N2O) (46 %), followed by methane (CH4) (45%) and Carbon
dioxide (CO2) (9%) (Baumert et al. 2005). N2O is classified as long-lived GHG
and has a global warming potential (GWP) 300 times higher than that of CO2. The
N2O concentration in 2005 was 319 ppb, about 18% higher than its pre-industrial
value (IPCC 2007). Oil palm is one of the most rapidly increasing crops in the
tropics (Fitzherbert et al. 2008). Malaysia and Indonesia began to dominate oil
palm production in 1966 (Poku 2002) and Indonesia has been the largest producer
of Crude Palm Oil (CPO) since 2005. In 2006 the country had 4.1 million ha of oil
palm plantations or 31% worldwide plantation area (Koh and Wilcove 2008).
Conversion of primary forests into oil palm plantations accounted for more than
10 % of deforestation in Indonesia and Malaysia between 1990 and 2010 (Koh et
al. 2011) causing large biodiversity losses and contributing to climate change
(Murdiyarso et al. 2010, Hergoualc’h and Verchot 2011). On the other hand, oil
palm is also a major driver of economic growth and a source of alternative fuel
(Sheil et al. 2009). Peatlands are classified as marginal due to their poor chemical
and physical soil properties (nutrient limited) (Murdiyarso et al. 2010, Sabiham
2010). The addition of nutrient such as fertilizer to promote plantation
productivity are likely to increase oxidation of soil organic matter and stimulating
an increased soil CO2 and N2O emission (Murdiyarso et al. 2010, Hadi et al.
2001).
The objectives of this study were (a) to investigate the impact of N dose
applied on soil N2O emissions (b) to assess soil emissions relationship to key
environmental variables including soil moisture, temperature, water filled pore
space (WFPS) and nitrogen availability.
We observed majority positive fluxes (85%) during the 6 months
measurement. Fluxes data were most negative and low during drier days in
particular on 23 and 25 October. We observed increasing N2O fluxes 10 days
after fertilization in all N treatments following the rain events. Emission peak was
noticed 19 days after fertilization but didn’t seem to be related to the N
application.
We found significant relationship (P=0.05) between water level, volumetric
water content, WFPS, gravimetric water content and N2O but R2 was really low
(R2 =0.02, R2=0.08, R2=0.02, R2=0.03 respectively). No significant relationship
also found between soil NH4+, NO3ˉ and N2O emissions. However, N2O was
significantly related to ratio of NO3ˉ/ NO3ˉ+ NH4+ for both analysis before and
after incubation (R2= 0.16 P= 0.02, R2= 0.17 P=0.02 respectively).
The magnitude of N2O emissions of our study was much larger than what
reported in the literature for oil palm plantations on peat (Melling et al. 2007).
The authors measured annual N2O emissions of 1.2 kg N ha-1 year-1 ranging from
0.9 to 58.4 mg N m-2 h-1 in a 4 year old plantation fertilized at a rate of 103 kg N
ha-1 year-1. Our study found N2O emissions were 18, 10 and 20 fold higher than
this literature for N0, N1 and N2 respectively. Our study however found closer
result to IPCC (2006) emission factor for croplands on organic soil which is 16 kg
N ha-1 y-1.
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All right reserved
Unless otherwise indicated, all materials on this thesis are copyrighted by the
Bogor Agricultural University. All rights reserved. No part of these pages, either
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THE EFFECT OF NITROGEN FERTILIZATION ON
SOIL N2O EMISSIONS FROM OIL PALM CULTIVATION
ON DEEP PEAT
SATRIA OKTARITA
Thesis
submitted to meet requirements for an award
Magister of Science at Natural Resource and Environmental
Management
GRADUATE SCHOOL
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
2014
External examiner:
Dr Ir Budi Nugroho, MSi
Title
Name
ID
: The Effect of Nitrogen Fertilization on Soil N2O Emissions from
Oil Palm Cultivation on Deep Peat
: Satria Oktarita
: P052110221
Approved by
Supervising committee
Dr Ir Syaiful Anwar, MSc
Head
Dr Kristell Hergoualc’h
Member
Endorsed by
Head of Natural Resources and
Environmental Management
Dean of Graduate School
Prof Dr Ir Cecep Kusmana,MS
Dr Ir Dahrul Syah, MScAgr
Defense date :
Graduated Date :
FOREWORDS
I would like to thanks my supervisors, Dr. Syaiful Anwar MSc and
Dr. Kristell Hergoualc’h for their guidance, comments, discussions and
suggestions to finish this study. I would also like to thanks my husband for the
encouragements and my assistants, Ferdy and Fadly, for their hard work to assist
in collecting data. I am also indebted to Novi and Melly for their hard work to
analyze my samples.
This study was generously supported by the governments of Norway and
Australia. This work was carried out as part of the CGIAR programs on Trees,
Forests and Agroforestry (CRP6) and Climate Change, Agriculture and Food
Security (CCAFS).
Bogor, March 2014
Satria Oktarita
TABLE OF CONTENTS
LIST OF TABLES
vi
LIST OF FIGURES
vi
1 INTRODUCTION
Background
Objectives
Research Benefit
Scope of Research
7
7
2
2
2
2 LITERATURE REVIEW
Peatlands
Oil Palm
Nitrogen Cycling
Factors Influence Soil fluxes
3
3
3
3
4
3 METHOD
Site Description
Experimental Design
Equipments and Materials
Data Analysis
5
5
5
6
7
4 RESULT AND DISCUSSION
Result
Discussion
8
8
13
5 CONCLUSION AND SUGGESTION
Conclusion
Suggestion
14
14
14
REFERENCES
14
BIOGRAPHY
19
LIST OF TABLES
1 Fertilizer events of N1 Plot
2 Water level, gravimetric water content, volumetric water content
and WFPS during the study period
3 Ammonium, Nitrate, Net Mineralization and Nitrification for the
different N treatment
6
9
10
LIST OF FIGURES
1 Major transformation in nitrogen cycle
2 Monthly rainfall (a), air temperature (b) and soil temperature (c)
) N1 (
)
in the top 10 cm of the soil profile for N0 (
and N2 (
)
3 Monthly fluxes (g N ha-1 d-1) of N0( ),N1 ( ),N2( ) in the
oil palm plantation, Jambi, Sumatra, Indonesia
), FP (
) for N0, N1 and
4 N2O Fluxes (mean ± SE) of CP (
N2 during intensive sampling (d-1 to d+29)5
5 Fluxes and its relationship with environment variables
4
9
11
12
13
1 INTRODUCTION
Background
Agriculture contributes to 13.5% of worldwide greenhouse gases (GHG)
emissions (IPCC 2007). The emissions from this sector are mainly in the form of
nitrous oxide (N2O) (46 %), followed by methane (CH4) (45%) and Carbon
dioxide (CO2) (9%) (Baumert et al. 2005). N2O is classified as long-lived GHG
and has a global warming potential (GWP) 300 times higher than that of CO2. The
N2O concentration in 2005 was 319 ppb, about 18% higher than its pre-industrial
value (IPCC 2007). N2O emissions largely come from soil management including
tillage and other cropping practices, such as fertilizer application (Baumert et al.
2005). Worldwide consumption of synthetic N fertilizers has increased by about
150% since 1970 to about 82 Tg N y-1 in 1996 (IPCC 2000).
Oil palm is one of the most rapidly increasing crops in the tropics
(Fitzherbert 2008). Malaysia and Indonesia began to dominate oil palm production
in 1966 (Poku 2002) and Indonesia has been the largest producer of Crude Palm
Oil (CPO) since 2005. In 2006 the country had 4.1 million ha of oil palm
plantations or 31% worldwide plantation area (Koh and Wilcove 2008).
According to Rahutomo et al. (2009) oil palm plantations are distributed in all
over twenty two provinces. In 2010 the plantation area was 7.2 million ha
producing 46% of the world’s crude palm oil (Bromokusumo and Slette 2010).
Recent data on oil palm area for 2012 was estimated at around 9.2 million ha
(MoA 2012).
Conversion of primary forests into oil palm plantations accounted for more
than 10 % of deforestation in Indonesia and Malaysia between 1990 and 2010
(Koh et al. 2011) causing large biodiversity losses and contributing to climate
change (Murdiyarso et al. 2010, Hergoualc’h and Verchot 2011). On the other
hand, oil palm is also a major driver of economic growth and a source of
alternative fuel (Sheil et al. 2009). The growing trend is likely to continue in the
future as Indonesia aimed at doubling-up oil-palm production by 2020 (Koh and
Ghazoul 2010). The Indonesian government allows the development of oil palm
plantations on marginal lands such as peatlands however forbids plantation on
peat deeper than 3 m (RSPO 2012). Furthermore, according to the regulation oil
palm can only be grown on sapric and eutrophic peat. So far 11% of the
plantations are located on peatlands (Koh et al. 2011). The Presidential Instruction
(Inpres) No. 10/2011 which is part of bilateral cooperation between the
governments of Indonesia and Norway (Murdiyarso et al. 2011) postpones the
issuance of new licenses on primary natural forests and peatlands for area
included in the indicative map.
Peatlands are classified as marginal due to their poor chemical and physical
soil properties (nutrient limited) (Murdiyarso et al. 2010, Sabiham 2010).
According to Riwandi (2002), oil palm needs intensive N, P and K amendments
with doses depending on the site characteristics. Nitrogen fertilizer doses
recommended by Ministry Agriculture for oil palm cultivated on peat range from
3.45- 34.5 kg N ha-1 for young stand (1-32 months) to 103-172.5 kg N ha-1 for
2
mature palm (3-25 years). The addition of nutrient such as fertilizer to promote
plantation productivity are likely to increase oxidation of soil organic matter and
stimulating an increased soil CO2 and N2O emission (Murdiyarso et al. 2010,
Hadi et al. 2001).
The production and consumption of N2O in the soil is mainly due to the
activity of soil microbes through nitrification and denitrification process (Smith et
al. 1982, Davidson et al. 2000, Murdiyarso et al. 2010). Nitrification is the
aerobic microbial oxidation of ammonium (NH4+) to to nitrate (NO3-) and
denitrification is the anaerobic microbial reduction of nitrate (NO3-) to nitrogen
gas (N2). Nitrous oxide is a gaseous intermediate in the reaction sequence of
denitrification and a by-product of nitrification that leaks from microbial cells into
the soil and ultimately into the atmosphere (Bouwman 1998, Smith et al. 2003,
IPCC 2006, Jauhiainen et al. 2012). The controlling factors of the flux include
soil moisture and temperature (Hadi et al. 2001, Inubushi et al. 2003, Hadi et al.
2005, Melling et al. 2007), nitrogen availability (Smith et al. 1982, Bouwman
1998, Davidson et al. 2000, Verchot et al. 2006, Melling et al. 2007). The effect
of soil water content on soil N2O effluxes described as a monotonic curve with
maximum emissions around 60% of water-filled pore space (WFPS) (Bouwman
1998, Murdiyarso et al. 2010). Studies have also shown that N2O emission and
water content can be positively and negatively correlated (Davidson et al. 2000).
cou.
There has been, to our knowledge, only one publication reporting soil N2O
fluxes from oil palm plantations on tropical peats (Melling et al. 2007). The
authors measured annual N2O emissions of 1.2 kg N ha-1 year-1 ranging from 0.9
to 58.4 mg N m-2 h-1 in a 4 year old plantation fertilized at a rate of 103 kg N ha-1
year-1. This study however didn’t capture the magnitude and dynamics of
emissions following fertilizer application.
Objectives
The objectives of this study were (a) to investigate the impact of N dose
applied on soil N2O emissions (b) to assess soil emissions relationship to key
environmental variables including soil moisture, temperature, water filled pore
space (WFPS) and nitrogen availability.
Research Benefit
This research is the first one evaluating the effect of N fertilization on soil
N2O emission from oil palm plantations on peat. The knowledge will be useful for
plantation developers, government agencies and related stakeholders in their
efforts and policies to implement sustainable oil palm management in peat lands
and evaluate impacts on climate change.
Scope of Research
This research will focus on short term (6 months) and immediate effect of
nitrogen fertilization on soil N2O emissions.
3
2 LITERATURE REVIEW
2.1 Peatlands
Peat is traditionally defined as being synonymous with turf being partially
carbonized plant tissue formed in wet conditions by decomposition of various
plants. The different between tropical wetland and other wetlands which influence
management is the nature of the organic soils. This is because the plants from
which the peat is formed are different. In the tropics, trees are frequently involved
as opposed to sedges and sphagnum moss in temperate regions (Andriesse 1988).
Peat (and carbon) accumulates as a result of a positive net imbalance between
high tropical ecosystem primary production and incomplete organic matter
decomposition in permanently saturated soil conditions, the organic matter
originated from plant residue and plant tissue. Generally peat was formed in the
alluvial plain, especially in the basin between big rivers. Based on fertility, peat
soil can be differentiated as oligotrophic, mesotrophic, and eutrophic.
Oligotrophic is unfertile peat that is poor of bases. Eutrophic is fertile peat which
is rich in minerals and bases, while mesotrophic is peat that has properties in
between oligotrophic and eutrophic (Hooijer et al. 2010, Presetyo and Suharta,
2011).
2.2 Oil Palm
Oil Palm (Elaeis guineensis) is a tropical palm native to West and Central
Africa. Grown in plantations it produces 3–8 times more oil from a given area
than any other tropical or temperate oil crop. Oil (triacylglycerols) can be
extracted from both the fruit and the seed, crude palm oil (CPO) from the outer
mesocarp and palm-kernel oil from the endosperm. Most crude palm oil is used in
foods. In contrast, most palm-kernel oil is used in various non-edible products,
such as detergents, cosmetics, plastics, surfactants, herbicides, as well as a broad
range of other industrial and agricultural chemicals (Wahid et al. 2005).
The native habitat of oil palm is tropical rainforest with 1780–2280 mm
annual rainfall and a temperature range of 24–30°C (minimum and maximum),
seedlings do not grow below 15°C. Oil palm is tolerant of a wide range of soil
types, as long as it is well watered (NewCROP 1996). Oil palm needs humid
equatorial conditions to thrive, and conditions in Southeast Asia are ideal.
Seasonal droughts at higher tropical latitudes greatly reduce yields (Basiron
2007), water-stressed palms produce fewer female flowers and abort (drop) unripe
fruit. Palm productivity benefits from direct sunshine: the lower incidence of
cloud cover over much of Southeast Asia is thought to be one reason why oil palm
yields are higher than that in West Africa (Dufrene et al. 1990).
2.3 Nitrogen Cycling
The primary driver for the industrial era increase of N2O was concluded to
be enhanced microbial production in expanding and fertilized agricultural lands.
The increase in N2O since the pre-industrial era now contributes a radiative
forcing of +0.16 ± 0.02 W m–2 and is due primarily to human activities,
particularly agriculture and associated land use change. Current estimates are that
4
about 40% of total N2O emissions are anthropogenic but individual source
estimates remain subject to significant uncertainties. Long-lived greenhouse gases
(LLGHGs), for example, CO2, methane (CH4) and nitrous oxide (N2O), are
chemically stable and persist in the atmosphere over time scales of a decade to
centuries or longer, so that their emission has a long-term influence on climate.
Because these gases are long lived, they become well mixed throughout the
atmosphere much faster than they are removed and their global concentrations can
be accurately estimated from data at a few locations (IPCC 2007).
The production and consumption of N2O in the soil is mainly due to the
activity of soil microbes through nitrification and denitrification process (Smith et
al. 1982, Davidson et al. 2000, Murdiyarso et al. 2010). Nitrification is the
aerobic microbial oxidation of ammonium (NH4+) to to nitrate (NO3-) and
denitrification is the anaerobic microbial reduction of nitrate (NO3-) to nitrogen
gas (N2). Nitrous oxide is a gaseous intermediate in the reaction sequence of
denitrification and a by-product of nitrification that leaks from microbial cells into
the soil and ultimately into the atmosphere (Bouwman 1998, Smith et al. 2003,
IPCC 2006, Jauhiainen et al. 2012).
Figure 1 Major transformations in nitrogen cycle (from Bernhard 2012)
2.4 Factors influence Soil fluxes
The controlling factors of the flux include soil moisture and temperature
(Hadi et al. 2001, Inubushi et al. 2003, Hadi et al. 2005, Melling et al. 2007),
nitrogen availability (Smith et al. 1982, Bouwman 1998, Davidson et al. 2000,
Verchot et al. 2006, Melling et al. 2007). The effect of soil water content on soil
N2O effluxes described as a monotonic curve with maximum emissions around
60% of water-filled pore space (WFPS) (Bouwman 1998, Murdiyarso et al.
2010). Studies have also shown that N2O emission and water content can be
positively and negatively correlated (Davidson et al. 2000).
5
3 METHOD
Site Description
Flux measurements were conducted at an oil palm plantation located at
Arang-arang village in Muaro Jambi district. The annual rainfall is 2144 mm y-1
with an average air temperature of 28.8°C. The peat at the research site is deep (>
8.5 m) and slightly decomposed (fibric). The site was cleared of native vegetation
in 2004 and planted in December 2009 with 148 palms ha-1. Planting distance is 9
m in a triangular pattern. Halfway to the site can be reached by car but the rest is
only accessible by tractor. Drainage canals in the plantation are deeper than 4
meters. The first fertilization was carried out on March 2010 when the palms were
3 month old. The palms receive fertilizer twice a year in March and September
until they reach maturity at about 3 years. After they reach maturity, the palms are
fertilized once per year in April.
Experimental Design
We used 3 nitrogen doses in the form of urea (N0, N1, N2) of 0 kg N ha-1
y , 51 kg N ha-1 y-1 and 102 kg N ha-1 y-1, respectively. 10 replicate chambers
were installed in each N dose treatment. 5 chambers were placed near the palm
and 5 others at mid-distance between two palms. Fertilizer was applied in circle
1m around oil palm. In the N1 and N2 treatments, the 5 chambers placed close to
the palms receive 750 g urea and 1500 g urea, respectively. This area will be
referred to as the close to palm (CP), while the other 5 chambers that are not
receiving fertilizer will be referred to as the further from palm (FP). As we
described above chamber was placed inside this circle area (CP). Amount of urea
spread in the chamber was calculated based on the relative area of chamber
surface to the total surface of fertilizer circle. This is to make sure that we applied
N fertilizer in the chamber based on the assumption that it is distributed evenly.
Radius and basal area of oil palm was also taken into consideration in the
calculation. Fertilization events of N1 plot can be found in table 1. N2 Plot doses
were always the doubled of N1.
-1
Table 1 Fertilizer events of N1 Plot
Month
March 2010
September 2010
March 2011
September 2011
March 2012
October 2012
April 2013
Age
(months)
3
9
15
21
27
34
40
g urea
palm-1
100
200
300
400
750
750
1500
gN
palm-1
46
92
138
184
345
345
690
kg urea
ha-1 y-1
15
30
44
59
111
111
222
kg N
ha-1 y-1
7
14
20
27
51
51
102
6
Equipments and Materials
Soil Flux Measurement
Soil fluxes were measured using the static chamber technique (Verchot et
al. 1999) from October 2012 until March 2013 using PVC made chambers
(diameter and height of 26 cm and 40 cm, respectively). Chambers were pushed
into the soil to a depth of 2–3 cm. Gas samples were collected on 0, 10, 20 and 30
minutes after closure using a 50 ml syringe and stored in a 40 ml customized glass
vials. Gas samples were transported to CIFOR's laboratory in Jambi for further
analysis by gas chromatography. Samples were analyzed within 30 days after
collection. We modified Shimadzu GC 14 A, 2 valco valves with a computerized
injection system to enable the machine analyze 60 samples sequentially. Nitrogen
was used as carrier gas to transport samples through a stainless steel column
equipped with Flame Ionization Detector (FID) for CH4 and Electron Capture
Detector (ECD) for N2O. The column is 3 m long packed by porapak Q with 80100 mesh.
Climatic data such as rainfall, air pressure and temperature were also
collected. Rainfall data collected from a rain gauge installed around 3 km from the
plot. A digital barometer from greisinger electronic (Germany) was used to
measure air pressure at each sampling time for each chamber. Environmental
factors were also obtained namely soil temperature, gravimetric moisture, WFPS
and nitrogen availability. Soil temperature was measured using a digital soil
thermometer v.GTH 1170 from greisinger electronic. Soil moisture kit from
Delta-T Devices Ltd (UK) was employed to measure gravimetric soil moisture.
The soil water-filled pore space (WFPS) was calculated based on Haney and
Haney (2010):
Soil water content (g g-1) = Weight of moist soil- Weight of oven dried soil
Weight of oven dried soil
Soil bulk density (gcm-3) = Weight of oven dried soil
Volume of soil
Soil porosity (%) =
Soil bulk density
Soil particle density (assumed to be 1.5 g cm-3)
Volumetric water content (g cm-3) = Soil water content x bulk density
WFPS (%) = Volumetric water content x 100
Soil porosity
Flux Calculation
Gas fluxes were calculated from the rate of change of N2O concentration in
the chamber headspace, determined by linear regression based on the four samples
(Verchot et al. 1999). The slope of the best linear fit is expressed in mass units
per space by using the ide al gas law:
N2O (µ N2O m-2 h-1) = N2O x Pressure x 28 x Chamber height
Air temp x Gas Constant
7
Where N2O is rate of N2O concentration in ppm N2O m-2 h-1 in the chamber
headspace, pressure is air pressure in pascal (Pa), 28 g mole-1 is the mass of N (14
g 2) per mole of N2O, chamber height is in meter, air temperature is in Kelvin
(273+°C), gas contant is 8.31441 j k-1 mol-1.
Nitrogen Availability
Laboratory incubations were carried out to measure the rates of net
mineralization and net nitrification. Soil samples were collected on February
2013. One soil sample per chamber collected within 0-10 cm depth. Samples
transported to the laboratory and refrigerated until incubation. The coarse roots
and organic matter detritus was manually removed from the soil samples. The
procedure described by Hart et al. (1994) was used to determine net
mineralization and net nitrification. A 10-g soil subsample was extracted in 100
ml of 2M KCl to determine inorganic N concentrations. These extracts were
shaken for an hour with magnetic stirrer and settled for 24 hours. A 20-mL
aliquot of the supernatant was removed, filtered through a grade no.42 whatmann
filter paper and frozen for later analysis. NH4+ analysis was done on auto analyzer
from Bran LuebbeTM using colorimetric method with indophenols blue (Solorzano
1969). Determination of NO3- was done on U-2001 spectrophotometer from
Hitachi using brucine procedure (EPA 1971). A second subsample of 10 g was
incubated in the dark at room temperature (25-28°C) for 10 days. After 10 days,
the incubated sample was extracted according to the procedures described above
The net N mineralization rate was calculated as the change in NH4+ + NO3concentration during the 10 day incubation. Net nitrification rate was calculated
as the difference between initial and final NO3- concentrations.
Data Analysis
Statistical analysis was done with SPSS software v.19. The data set showed
a non-normal distribution (Shapiro-Wilk test). A log transformation of the data set
was performed as an attempt to fix the distribution but gave unsatisfactory result.
Thus differences in N2O emission among N doses determined using non
parametric analysis (Kruskal Wallis Test). Simple regression analyses were
carried out to examine relationships between N2O emission and environmental
variables.
8
4 RESULT AND DISCUSSION
Result
Climatic observation
During our study period, there was no clear distinction between dry and
wet season. Rainfall was highest in December 2012 (354 mm) and lowest in
January 2013 (36.42 mm). Flux data were collected in the field around 9 am to 2
pm. Thus, every month we rotated the measurement time for each plot in order to
capture the variability. Air temperature fluctuated throughout the measurements
from 24.6°C to 49.6°C with high relative humidity. While air temperature
fluctuates during the day, mean of soil temperature remains stable at around 28°C.
The first fertilization treatment was conducted on 23 October 2012. We observed
no rain event on the fertilization day and 2 days after fertilization (0 mm). In
opposite, the second fertilization on 18 April 2013 was done during rainy season
where rainfalls continuously occurred one week after fertilization.
-1
Rainfall (mm month )
400
(a)
300
200
100
(b)
Air Temp (°C)
0
46
44
42
40
38
36
34
32
30
30
Soil Temp (°C)
(c)
29
28
27
26
Oct
Nov
Dec
Jan
Feb
Mar
Figure 2 Monthly rainfall (a), air temperature (b) and soil temperature (c) in the
top 10 cm of the soil profile for N0 ( ) N1 (
) and N2 (
)
9
Water level (WL) ranges from -36.5 cm to -85.5cm. We cannot measure
WL data on December 2012 when rainfall was the highest. Based on 5 months
observations (23 measurements), there was no clear relationship across WFPS,
mG, mV, WL and rainfall. We observed weak relationship also between mV and
WFPS.
Table 2 Water level (WL), gravimetric water content (mG), volumetric water
content (mV) and WFPS during study period
Month
WL
mG
mV
WFPS
(-cm)
(g g-1 d.w.)
(m3 m-3 d.w)
(%)
59.29 (0.87)c
65.14 (1.04)b
October
2.48(0.01)bc 0.44(0.01)ab
0.51(0.01)c
59.94 (0.74)c
November 56.80 (0.55)a
1.22(0.07)a
n.a
54.62 (3.01)bc
n.a
December
2.02(0.11)b
0.48 (0.02)bc
56.64 (2.60)c
62.17 (0.31)ab 1.23(0.04)a
January
n.a
31.67 (2.60)a
62.33 (0.93)ab 1.17(0.10)a
February
0.40 (0.02)a
46.69(2.70)b
58.00 (3.63)a
March
2.94(0.03)c
Values are mean ± standard error (in parenthesis)
Means with the same letter are not significantly different
n.a. is not available due to missing data.
Nitrogen Availability
Inorganic N pools were dominated by NH4+ in all N treatments (Table 3).
Soil sampling was conducted on February. Soil NH4-N concentration at N0, N1,
N2 varied from 19.94 to 188.32, 47 to 290.42, 2.49 to 42.72, respectively. We
observed some high NH4+ concentrations at N1 and as expected it came from the
CP zone. NO3-N concentration at N0,N1,N2 ranged from 0.08 to 18.45, 0.19 to
14.93, 0.46 to 15.28 respectively. In summary, we observed higher N availability
at N0, N1 than that of N2 treatment. We found significant different among N
treatments for NH4+ (P=0.0002). However there were no significant found on
NO3-, net mineralization and net nitrification among the N treatments (P=0.77,
P=0.25, P=0.05 respectively). The result of net mineralization showed majority
positive value which indicate no NO3- loss during incubation.
Table 3 Ammonium, Nitrate, Net Mineralization and Nitrification for the
different N treatment
Treatment
N- NH4+, N- NO3-,
mg N kg-1 mg N kg-1
d.w.
d.w.
Net
Mineralization
(mg N kg-1 d-1)
89.39b
6.03a
4.73a
N0
114.65b
5.59a
5.94a
N1
17.73a
5.40a
2.62a
N2
Means with the same letter are not significantly different
Net
Nitrification
(mg N kg-1 d-1)
0.89a
0.83a
0.24a
10
3.3
N2O Fluxes
We observed majority positive fluxes (85%) during the 6 months
measurement. N2O fluxes from the soil showed seasonal fluctuation. Fluxes data
were most negative and low during drier days in particular on 23 and 25 October
and high relatively high in December. We observed low emissions in March
despite the high monthly rainfall due low rainfall during measurement and two
days before measurement. Few negative fluxes were also recorded during the
relatively wet days. Monthly fluxes were calculated from the average of ten
chambers (n=10) for each plot except for October and November when we
conducted intensive sampling of 9 (n=90) and 11 (n=110) days respectively. This
is to ensure a robust calculation that avoid under or over estimation. N2O
Emissions remain low on October at the fertilization plot (N1 and N2). It
increased on November and December following the rain events with a similar
magnitude for all N treatments and control. Emission relatively similar on
January, February and March. We observed high variability of fluxes on
December for all N treatments.
N 2O Flux (g N-N 2O ha-1 d-1)
350
300
250
200
150
100
50
0
Oct
Nov
Dec
Jan
Feb
Mar
Figure 3 Monthly fluxes (g N ha-1 d-1) of N0( ),N1 ( ),N2( )
in the oil palm plantation, Jambi, Sumatra, Indonesia
3.4
Intensive Sampling
We examined the dynamic and magnitude of N2O emission after
fertilization through an intensive samplings on October and November. We
observed increasing N2O fluxes 10 days after fertilization in all N treatments
following the rain events. Emission peak was noticed 19 days after fertilization
but didn’t seem to be related to the N application. We found CP was higher than
FP at N1 treatment 19 days after fertilization, however they were not significantly
different. We also observed higher CP fluxes than that of FP at N2 treatment in
11
day 2 and 3 after fertilization. Overall, we didn’t see the effect of fertilizer in both
N1 and N2 treatment.
(N0)
N2O (g N-N2O ha-1 d-1)
250
200
150
100
50
0
(N1)
N2O (g N-N2O ha-1 d-1)
300
250
200
150
100
50
0
(N2)
N2O (g N-N2O ha-1 d-1)
250
200
150
100
50
0
-1 0 1 2 4 5 6 7 9 11 13 15 17 19 21 23 25 27 29
Days after fertilization
Figure 4 N2O Fluxes (mean ± SE) of CP (
), FP (
during intensive sampling (d-1 to d+29)
3.5
) for N0, N1 and N2
N2O Fluxes and its controlling factor
We observed maximum fluxes were occurred when water level (WL) was
around -60 cm. Fluxes seem to decrease when WL lower than -60cm. N2O
emission were maximum at WFPS around 60-80 %. Fluxes also maximum when
soil temperatures were 28-29 ºC. Fluxes were decreasing when temperature above
30 ºC. We found significant relationship across all measured environmental
factors, however R2 was really low. Gravimetric and volumetric water content
were significantly related to water level (P=0.01 R2=0.006, P
SOIL N2O EMISSIONS FROM OIL PALM CULTIVATION
ON DEEP PEAT
SATRIA OKTARITA
GRADUATE SCHOOL
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
2014
STATEMENT OF THESIS, SOURCES OF INFORMATION
AND COPYRIGHT*
I hereby certify that this thesis entitled The Effect of Nitrogen Fertilization
on Soil N2O Emissions from Oil Palm Cultivation on Deep Peat is my work under
the supervising committee and never been submitted in any form to any higher
education institution. Materials previously published or written by other person
mentioned in the text and listed in the Bibliography at the end of this thesis.
I hereby bestow the copyright of my papers to the Bogor Agricultural
University.
Bogor, March 2014
Satria Oktarita
ID P052110221
RINGKASAN
SATRIA OKTARITA. Dampak Pemupukan Nitrogen Terhadap Emisi N2O Tanah
Pada Perkebunan Sawit di Gambut Dalam. Dibimbing oleh SYAIFUL ANWAR
dan KRISTELL HERGOUALC’H.
Sektor pertanian berkontribusi 13.5% dari total emisi Gas Rumah Kaca
(GRK) dunia (IPCC 2007). Emisi dari sektor ini umumnya dalam bentuk
dinitrogen oksida (N2O) (46%), metana (CH4) (45%) dan karbon dioksida (CO2)
(9%) (Baumert et al. 2005). N2O termasuk dalam GRK berumur panjang and
memiliki potenti gas rumah kaca (GWP) 300 kali lebih tinggi dibanding CO2.
Konsentrasi N2O pada tahun 2005 adalah sebesar 319 ppb dimana konsentrasi ini
lebih tinggi 18% jika dibanding konsentrasi sebelum masa industrialisasi (IPCC
2007). Sawit merupakan salah satu komoditas yang berkembang sangat pesat di
daerah tropis (Fitzherbert et al. 2008). Malaysia dan Indonesia mulai
mendominasi produksi minyak sawit sejak tahun 1966 (Poku 2002) dan Indonesia
menjadi negara produsen minyak sawit mentah (CPO) terbesar didunia sejak
tahun 2005. Pada tahun 2006 Indonesia memiliki 4.1 juta hektar perkebunan sawit
atau sekitar 31% dari luas total perkebunan sawit diseluruh dunia (Koh dan
Wilcove 2008). Konversi hutan alam menjadi perkebunan sawit berkontribusi
terhadap 10% deforestasi di Indonesia dan Malaysia pada tahun 1990 hingga 2010
(Koh et al. 2011) menyebabkan hilangnya keanekaragaman hayati dan
berkontribusi terhadap perubahan iklim (Murdiyarso et al. 2010, Hergoualc’h dan
Verchot 2011). Disisi lain sawit merupakan salah satu penyumbang pertumbuhan
ekonomi dan sumber bahan bakar alternatif (Sheil et al. 2009).
Gambut diklasifikasikan sebagai lahan marginal karena miskin hara
(Murdiyarso et al. 2010, Sabiham 2010). Penambahan nutrisi tanah misalnya
pupuk untuk meningkatkan hasil pr
oduski dapat meningkatkan oksidasi bahan organik tanah dan meningkatkan
emisi CO2 dan N2O dari tanah (Murdiyarso et al. 2010, Hadi et al. 2001).
Tujuan penelitian adalah untuk (a) mengukur dampak dosis pupuk nitrogen
terhadap emisis N2O tanah (b) mengetahui keterkaitan emisi tanah dengan
variabel lingkungan termasuk kelembaban tanah, suhu, pori tanah terisi air
(WFPS) dan ketersediaan nitrogen.
Selama masa pengukuran 85% flux tanah merupakan flux positif (emisi).
Flux negatif dan rendah ditemukan pada pengukuran yang dilakukan pada kondisi
kering terutama pada tanggal 23 dan 25 Oktober 2012. Peningkatan emisi N2O
terlihat 10 hari setelah pemupukan pada semua perlakuan setelah terjadinya hujan.
Puncak emisi terjadi 19 hari setelah pemupukan namun tidak sepenuhnya
disebabkan oleh aplikasi pupuk.
Hasil penelitian ini menunjukkan hubungan yang signifikan antara N2O
(P=0.05) dengan variabel lingkungan yaitu tinggi muka air, kadar air volumetrik,
WFPS, kadar air gravimetrik namun R2 sangat rendah (R2 =0.02, R2=0.08,
R2=0.02, R2=0.03). Tidak ditemukan hubungan yang nyata antara emisi N2O baik
dengan NH4+ maupun NO3ˉ. Namun, N2O memiliki hubungan yang nyata dengan
rasio NO3ˉ/ NO3ˉ+ NH4+ sebelum atau setelah inkubasi (R2= 0.16 P= 0.02, R2=
0.17 P=0.02).
Emisi N2O yang ditemukan dalam penelitian ini jauh lebih besar jika
dibandingkan dengan literatur dari penelitian terdahulu tentang emisi sawit yang
ditanam di daerah gambut (Melling et al. 2007). Penelitian terdahulu menemukan
emisi gambut tahunan sebesar 1.2 kg N ha-1 tahun-1 dengan kisaran flux antara 0.9
- 58.4 mg N m-2 h-1 pada perkebunan sawit berusia 4 tahun yang dipupuk dengan
nitrogen sebesar 103 kg N ha-1 tahun-1. Penelitian ini menemukan bahwa emisi
N2O masing-masing 18, 10 dan 20 kali lebih besar untuk N0, N1 dan N2. Kajian
ini mendapatkan emisi dengan nilai yang lebih dekat dengan default value IPCC
yaitu sebesar 16 kg N ha-1 tahun-1.
SUMMARY
SATRIA OKTARITA. The Effect of Nitrogen Fertilization on Soil N2O
Emissions from Oil Palm Cultivation on Deep Peat. Supervised by SYAIFUL
ANWAR and KRISTELL HERGOUALC’H.
Agriculture contributes to 13.5% of worldwide greenhouse gases (GHG)
emissions (IPCC 2007). The emissions from this sector are mainly in the form of
nitrous oxide (N2O) (46 %), followed by methane (CH4) (45%) and Carbon
dioxide (CO2) (9%) (Baumert et al. 2005). N2O is classified as long-lived GHG
and has a global warming potential (GWP) 300 times higher than that of CO2. The
N2O concentration in 2005 was 319 ppb, about 18% higher than its pre-industrial
value (IPCC 2007). Oil palm is one of the most rapidly increasing crops in the
tropics (Fitzherbert et al. 2008). Malaysia and Indonesia began to dominate oil
palm production in 1966 (Poku 2002) and Indonesia has been the largest producer
of Crude Palm Oil (CPO) since 2005. In 2006 the country had 4.1 million ha of oil
palm plantations or 31% worldwide plantation area (Koh and Wilcove 2008).
Conversion of primary forests into oil palm plantations accounted for more than
10 % of deforestation in Indonesia and Malaysia between 1990 and 2010 (Koh et
al. 2011) causing large biodiversity losses and contributing to climate change
(Murdiyarso et al. 2010, Hergoualc’h and Verchot 2011). On the other hand, oil
palm is also a major driver of economic growth and a source of alternative fuel
(Sheil et al. 2009). Peatlands are classified as marginal due to their poor chemical
and physical soil properties (nutrient limited) (Murdiyarso et al. 2010, Sabiham
2010). The addition of nutrient such as fertilizer to promote plantation
productivity are likely to increase oxidation of soil organic matter and stimulating
an increased soil CO2 and N2O emission (Murdiyarso et al. 2010, Hadi et al.
2001).
The objectives of this study were (a) to investigate the impact of N dose
applied on soil N2O emissions (b) to assess soil emissions relationship to key
environmental variables including soil moisture, temperature, water filled pore
space (WFPS) and nitrogen availability.
We observed majority positive fluxes (85%) during the 6 months
measurement. Fluxes data were most negative and low during drier days in
particular on 23 and 25 October. We observed increasing N2O fluxes 10 days
after fertilization in all N treatments following the rain events. Emission peak was
noticed 19 days after fertilization but didn’t seem to be related to the N
application.
We found significant relationship (P=0.05) between water level, volumetric
water content, WFPS, gravimetric water content and N2O but R2 was really low
(R2 =0.02, R2=0.08, R2=0.02, R2=0.03 respectively). No significant relationship
also found between soil NH4+, NO3ˉ and N2O emissions. However, N2O was
significantly related to ratio of NO3ˉ/ NO3ˉ+ NH4+ for both analysis before and
after incubation (R2= 0.16 P= 0.02, R2= 0.17 P=0.02 respectively).
The magnitude of N2O emissions of our study was much larger than what
reported in the literature for oil palm plantations on peat (Melling et al. 2007).
The authors measured annual N2O emissions of 1.2 kg N ha-1 year-1 ranging from
0.9 to 58.4 mg N m-2 h-1 in a 4 year old plantation fertilized at a rate of 103 kg N
ha-1 year-1. Our study found N2O emissions were 18, 10 and 20 fold higher than
this literature for N0, N1 and N2 respectively. Our study however found closer
result to IPCC (2006) emission factor for croplands on organic soil which is 16 kg
N ha-1 y-1.
© Copy Right of IPB, 2014
All right reserved
Unless otherwise indicated, all materials on this thesis are copyrighted by the
Bogor Agricultural University. All rights reserved. No part of these pages, either
text or image may be used for any purpose other than personal use. Therefore,
reproduction, modification, storage in a retrieval system or retransmission, in any
form or by any means, electronic, mechanical or otherwise, for reasons other than
personal use, is strictly prohibited without prior written permission.
THE EFFECT OF NITROGEN FERTILIZATION ON
SOIL N2O EMISSIONS FROM OIL PALM CULTIVATION
ON DEEP PEAT
SATRIA OKTARITA
Thesis
submitted to meet requirements for an award
Magister of Science at Natural Resource and Environmental
Management
GRADUATE SCHOOL
BOGOR AGRICULTURAL UNIVERSITY
BOGOR
2014
External examiner:
Dr Ir Budi Nugroho, MSi
Title
Name
ID
: The Effect of Nitrogen Fertilization on Soil N2O Emissions from
Oil Palm Cultivation on Deep Peat
: Satria Oktarita
: P052110221
Approved by
Supervising committee
Dr Ir Syaiful Anwar, MSc
Head
Dr Kristell Hergoualc’h
Member
Endorsed by
Head of Natural Resources and
Environmental Management
Dean of Graduate School
Prof Dr Ir Cecep Kusmana,MS
Dr Ir Dahrul Syah, MScAgr
Defense date :
Graduated Date :
FOREWORDS
I would like to thanks my supervisors, Dr. Syaiful Anwar MSc and
Dr. Kristell Hergoualc’h for their guidance, comments, discussions and
suggestions to finish this study. I would also like to thanks my husband for the
encouragements and my assistants, Ferdy and Fadly, for their hard work to assist
in collecting data. I am also indebted to Novi and Melly for their hard work to
analyze my samples.
This study was generously supported by the governments of Norway and
Australia. This work was carried out as part of the CGIAR programs on Trees,
Forests and Agroforestry (CRP6) and Climate Change, Agriculture and Food
Security (CCAFS).
Bogor, March 2014
Satria Oktarita
TABLE OF CONTENTS
LIST OF TABLES
vi
LIST OF FIGURES
vi
1 INTRODUCTION
Background
Objectives
Research Benefit
Scope of Research
7
7
2
2
2
2 LITERATURE REVIEW
Peatlands
Oil Palm
Nitrogen Cycling
Factors Influence Soil fluxes
3
3
3
3
4
3 METHOD
Site Description
Experimental Design
Equipments and Materials
Data Analysis
5
5
5
6
7
4 RESULT AND DISCUSSION
Result
Discussion
8
8
13
5 CONCLUSION AND SUGGESTION
Conclusion
Suggestion
14
14
14
REFERENCES
14
BIOGRAPHY
19
LIST OF TABLES
1 Fertilizer events of N1 Plot
2 Water level, gravimetric water content, volumetric water content
and WFPS during the study period
3 Ammonium, Nitrate, Net Mineralization and Nitrification for the
different N treatment
6
9
10
LIST OF FIGURES
1 Major transformation in nitrogen cycle
2 Monthly rainfall (a), air temperature (b) and soil temperature (c)
) N1 (
)
in the top 10 cm of the soil profile for N0 (
and N2 (
)
3 Monthly fluxes (g N ha-1 d-1) of N0( ),N1 ( ),N2( ) in the
oil palm plantation, Jambi, Sumatra, Indonesia
), FP (
) for N0, N1 and
4 N2O Fluxes (mean ± SE) of CP (
N2 during intensive sampling (d-1 to d+29)5
5 Fluxes and its relationship with environment variables
4
9
11
12
13
1 INTRODUCTION
Background
Agriculture contributes to 13.5% of worldwide greenhouse gases (GHG)
emissions (IPCC 2007). The emissions from this sector are mainly in the form of
nitrous oxide (N2O) (46 %), followed by methane (CH4) (45%) and Carbon
dioxide (CO2) (9%) (Baumert et al. 2005). N2O is classified as long-lived GHG
and has a global warming potential (GWP) 300 times higher than that of CO2. The
N2O concentration in 2005 was 319 ppb, about 18% higher than its pre-industrial
value (IPCC 2007). N2O emissions largely come from soil management including
tillage and other cropping practices, such as fertilizer application (Baumert et al.
2005). Worldwide consumption of synthetic N fertilizers has increased by about
150% since 1970 to about 82 Tg N y-1 in 1996 (IPCC 2000).
Oil palm is one of the most rapidly increasing crops in the tropics
(Fitzherbert 2008). Malaysia and Indonesia began to dominate oil palm production
in 1966 (Poku 2002) and Indonesia has been the largest producer of Crude Palm
Oil (CPO) since 2005. In 2006 the country had 4.1 million ha of oil palm
plantations or 31% worldwide plantation area (Koh and Wilcove 2008).
According to Rahutomo et al. (2009) oil palm plantations are distributed in all
over twenty two provinces. In 2010 the plantation area was 7.2 million ha
producing 46% of the world’s crude palm oil (Bromokusumo and Slette 2010).
Recent data on oil palm area for 2012 was estimated at around 9.2 million ha
(MoA 2012).
Conversion of primary forests into oil palm plantations accounted for more
than 10 % of deforestation in Indonesia and Malaysia between 1990 and 2010
(Koh et al. 2011) causing large biodiversity losses and contributing to climate
change (Murdiyarso et al. 2010, Hergoualc’h and Verchot 2011). On the other
hand, oil palm is also a major driver of economic growth and a source of
alternative fuel (Sheil et al. 2009). The growing trend is likely to continue in the
future as Indonesia aimed at doubling-up oil-palm production by 2020 (Koh and
Ghazoul 2010). The Indonesian government allows the development of oil palm
plantations on marginal lands such as peatlands however forbids plantation on
peat deeper than 3 m (RSPO 2012). Furthermore, according to the regulation oil
palm can only be grown on sapric and eutrophic peat. So far 11% of the
plantations are located on peatlands (Koh et al. 2011). The Presidential Instruction
(Inpres) No. 10/2011 which is part of bilateral cooperation between the
governments of Indonesia and Norway (Murdiyarso et al. 2011) postpones the
issuance of new licenses on primary natural forests and peatlands for area
included in the indicative map.
Peatlands are classified as marginal due to their poor chemical and physical
soil properties (nutrient limited) (Murdiyarso et al. 2010, Sabiham 2010).
According to Riwandi (2002), oil palm needs intensive N, P and K amendments
with doses depending on the site characteristics. Nitrogen fertilizer doses
recommended by Ministry Agriculture for oil palm cultivated on peat range from
3.45- 34.5 kg N ha-1 for young stand (1-32 months) to 103-172.5 kg N ha-1 for
2
mature palm (3-25 years). The addition of nutrient such as fertilizer to promote
plantation productivity are likely to increase oxidation of soil organic matter and
stimulating an increased soil CO2 and N2O emission (Murdiyarso et al. 2010,
Hadi et al. 2001).
The production and consumption of N2O in the soil is mainly due to the
activity of soil microbes through nitrification and denitrification process (Smith et
al. 1982, Davidson et al. 2000, Murdiyarso et al. 2010). Nitrification is the
aerobic microbial oxidation of ammonium (NH4+) to to nitrate (NO3-) and
denitrification is the anaerobic microbial reduction of nitrate (NO3-) to nitrogen
gas (N2). Nitrous oxide is a gaseous intermediate in the reaction sequence of
denitrification and a by-product of nitrification that leaks from microbial cells into
the soil and ultimately into the atmosphere (Bouwman 1998, Smith et al. 2003,
IPCC 2006, Jauhiainen et al. 2012). The controlling factors of the flux include
soil moisture and temperature (Hadi et al. 2001, Inubushi et al. 2003, Hadi et al.
2005, Melling et al. 2007), nitrogen availability (Smith et al. 1982, Bouwman
1998, Davidson et al. 2000, Verchot et al. 2006, Melling et al. 2007). The effect
of soil water content on soil N2O effluxes described as a monotonic curve with
maximum emissions around 60% of water-filled pore space (WFPS) (Bouwman
1998, Murdiyarso et al. 2010). Studies have also shown that N2O emission and
water content can be positively and negatively correlated (Davidson et al. 2000).
cou.
There has been, to our knowledge, only one publication reporting soil N2O
fluxes from oil palm plantations on tropical peats (Melling et al. 2007). The
authors measured annual N2O emissions of 1.2 kg N ha-1 year-1 ranging from 0.9
to 58.4 mg N m-2 h-1 in a 4 year old plantation fertilized at a rate of 103 kg N ha-1
year-1. This study however didn’t capture the magnitude and dynamics of
emissions following fertilizer application.
Objectives
The objectives of this study were (a) to investigate the impact of N dose
applied on soil N2O emissions (b) to assess soil emissions relationship to key
environmental variables including soil moisture, temperature, water filled pore
space (WFPS) and nitrogen availability.
Research Benefit
This research is the first one evaluating the effect of N fertilization on soil
N2O emission from oil palm plantations on peat. The knowledge will be useful for
plantation developers, government agencies and related stakeholders in their
efforts and policies to implement sustainable oil palm management in peat lands
and evaluate impacts on climate change.
Scope of Research
This research will focus on short term (6 months) and immediate effect of
nitrogen fertilization on soil N2O emissions.
3
2 LITERATURE REVIEW
2.1 Peatlands
Peat is traditionally defined as being synonymous with turf being partially
carbonized plant tissue formed in wet conditions by decomposition of various
plants. The different between tropical wetland and other wetlands which influence
management is the nature of the organic soils. This is because the plants from
which the peat is formed are different. In the tropics, trees are frequently involved
as opposed to sedges and sphagnum moss in temperate regions (Andriesse 1988).
Peat (and carbon) accumulates as a result of a positive net imbalance between
high tropical ecosystem primary production and incomplete organic matter
decomposition in permanently saturated soil conditions, the organic matter
originated from plant residue and plant tissue. Generally peat was formed in the
alluvial plain, especially in the basin between big rivers. Based on fertility, peat
soil can be differentiated as oligotrophic, mesotrophic, and eutrophic.
Oligotrophic is unfertile peat that is poor of bases. Eutrophic is fertile peat which
is rich in minerals and bases, while mesotrophic is peat that has properties in
between oligotrophic and eutrophic (Hooijer et al. 2010, Presetyo and Suharta,
2011).
2.2 Oil Palm
Oil Palm (Elaeis guineensis) is a tropical palm native to West and Central
Africa. Grown in plantations it produces 3–8 times more oil from a given area
than any other tropical or temperate oil crop. Oil (triacylglycerols) can be
extracted from both the fruit and the seed, crude palm oil (CPO) from the outer
mesocarp and palm-kernel oil from the endosperm. Most crude palm oil is used in
foods. In contrast, most palm-kernel oil is used in various non-edible products,
such as detergents, cosmetics, plastics, surfactants, herbicides, as well as a broad
range of other industrial and agricultural chemicals (Wahid et al. 2005).
The native habitat of oil palm is tropical rainforest with 1780–2280 mm
annual rainfall and a temperature range of 24–30°C (minimum and maximum),
seedlings do not grow below 15°C. Oil palm is tolerant of a wide range of soil
types, as long as it is well watered (NewCROP 1996). Oil palm needs humid
equatorial conditions to thrive, and conditions in Southeast Asia are ideal.
Seasonal droughts at higher tropical latitudes greatly reduce yields (Basiron
2007), water-stressed palms produce fewer female flowers and abort (drop) unripe
fruit. Palm productivity benefits from direct sunshine: the lower incidence of
cloud cover over much of Southeast Asia is thought to be one reason why oil palm
yields are higher than that in West Africa (Dufrene et al. 1990).
2.3 Nitrogen Cycling
The primary driver for the industrial era increase of N2O was concluded to
be enhanced microbial production in expanding and fertilized agricultural lands.
The increase in N2O since the pre-industrial era now contributes a radiative
forcing of +0.16 ± 0.02 W m–2 and is due primarily to human activities,
particularly agriculture and associated land use change. Current estimates are that
4
about 40% of total N2O emissions are anthropogenic but individual source
estimates remain subject to significant uncertainties. Long-lived greenhouse gases
(LLGHGs), for example, CO2, methane (CH4) and nitrous oxide (N2O), are
chemically stable and persist in the atmosphere over time scales of a decade to
centuries or longer, so that their emission has a long-term influence on climate.
Because these gases are long lived, they become well mixed throughout the
atmosphere much faster than they are removed and their global concentrations can
be accurately estimated from data at a few locations (IPCC 2007).
The production and consumption of N2O in the soil is mainly due to the
activity of soil microbes through nitrification and denitrification process (Smith et
al. 1982, Davidson et al. 2000, Murdiyarso et al. 2010). Nitrification is the
aerobic microbial oxidation of ammonium (NH4+) to to nitrate (NO3-) and
denitrification is the anaerobic microbial reduction of nitrate (NO3-) to nitrogen
gas (N2). Nitrous oxide is a gaseous intermediate in the reaction sequence of
denitrification and a by-product of nitrification that leaks from microbial cells into
the soil and ultimately into the atmosphere (Bouwman 1998, Smith et al. 2003,
IPCC 2006, Jauhiainen et al. 2012).
Figure 1 Major transformations in nitrogen cycle (from Bernhard 2012)
2.4 Factors influence Soil fluxes
The controlling factors of the flux include soil moisture and temperature
(Hadi et al. 2001, Inubushi et al. 2003, Hadi et al. 2005, Melling et al. 2007),
nitrogen availability (Smith et al. 1982, Bouwman 1998, Davidson et al. 2000,
Verchot et al. 2006, Melling et al. 2007). The effect of soil water content on soil
N2O effluxes described as a monotonic curve with maximum emissions around
60% of water-filled pore space (WFPS) (Bouwman 1998, Murdiyarso et al.
2010). Studies have also shown that N2O emission and water content can be
positively and negatively correlated (Davidson et al. 2000).
5
3 METHOD
Site Description
Flux measurements were conducted at an oil palm plantation located at
Arang-arang village in Muaro Jambi district. The annual rainfall is 2144 mm y-1
with an average air temperature of 28.8°C. The peat at the research site is deep (>
8.5 m) and slightly decomposed (fibric). The site was cleared of native vegetation
in 2004 and planted in December 2009 with 148 palms ha-1. Planting distance is 9
m in a triangular pattern. Halfway to the site can be reached by car but the rest is
only accessible by tractor. Drainage canals in the plantation are deeper than 4
meters. The first fertilization was carried out on March 2010 when the palms were
3 month old. The palms receive fertilizer twice a year in March and September
until they reach maturity at about 3 years. After they reach maturity, the palms are
fertilized once per year in April.
Experimental Design
We used 3 nitrogen doses in the form of urea (N0, N1, N2) of 0 kg N ha-1
y , 51 kg N ha-1 y-1 and 102 kg N ha-1 y-1, respectively. 10 replicate chambers
were installed in each N dose treatment. 5 chambers were placed near the palm
and 5 others at mid-distance between two palms. Fertilizer was applied in circle
1m around oil palm. In the N1 and N2 treatments, the 5 chambers placed close to
the palms receive 750 g urea and 1500 g urea, respectively. This area will be
referred to as the close to palm (CP), while the other 5 chambers that are not
receiving fertilizer will be referred to as the further from palm (FP). As we
described above chamber was placed inside this circle area (CP). Amount of urea
spread in the chamber was calculated based on the relative area of chamber
surface to the total surface of fertilizer circle. This is to make sure that we applied
N fertilizer in the chamber based on the assumption that it is distributed evenly.
Radius and basal area of oil palm was also taken into consideration in the
calculation. Fertilization events of N1 plot can be found in table 1. N2 Plot doses
were always the doubled of N1.
-1
Table 1 Fertilizer events of N1 Plot
Month
March 2010
September 2010
March 2011
September 2011
March 2012
October 2012
April 2013
Age
(months)
3
9
15
21
27
34
40
g urea
palm-1
100
200
300
400
750
750
1500
gN
palm-1
46
92
138
184
345
345
690
kg urea
ha-1 y-1
15
30
44
59
111
111
222
kg N
ha-1 y-1
7
14
20
27
51
51
102
6
Equipments and Materials
Soil Flux Measurement
Soil fluxes were measured using the static chamber technique (Verchot et
al. 1999) from October 2012 until March 2013 using PVC made chambers
(diameter and height of 26 cm and 40 cm, respectively). Chambers were pushed
into the soil to a depth of 2–3 cm. Gas samples were collected on 0, 10, 20 and 30
minutes after closure using a 50 ml syringe and stored in a 40 ml customized glass
vials. Gas samples were transported to CIFOR's laboratory in Jambi for further
analysis by gas chromatography. Samples were analyzed within 30 days after
collection. We modified Shimadzu GC 14 A, 2 valco valves with a computerized
injection system to enable the machine analyze 60 samples sequentially. Nitrogen
was used as carrier gas to transport samples through a stainless steel column
equipped with Flame Ionization Detector (FID) for CH4 and Electron Capture
Detector (ECD) for N2O. The column is 3 m long packed by porapak Q with 80100 mesh.
Climatic data such as rainfall, air pressure and temperature were also
collected. Rainfall data collected from a rain gauge installed around 3 km from the
plot. A digital barometer from greisinger electronic (Germany) was used to
measure air pressure at each sampling time for each chamber. Environmental
factors were also obtained namely soil temperature, gravimetric moisture, WFPS
and nitrogen availability. Soil temperature was measured using a digital soil
thermometer v.GTH 1170 from greisinger electronic. Soil moisture kit from
Delta-T Devices Ltd (UK) was employed to measure gravimetric soil moisture.
The soil water-filled pore space (WFPS) was calculated based on Haney and
Haney (2010):
Soil water content (g g-1) = Weight of moist soil- Weight of oven dried soil
Weight of oven dried soil
Soil bulk density (gcm-3) = Weight of oven dried soil
Volume of soil
Soil porosity (%) =
Soil bulk density
Soil particle density (assumed to be 1.5 g cm-3)
Volumetric water content (g cm-3) = Soil water content x bulk density
WFPS (%) = Volumetric water content x 100
Soil porosity
Flux Calculation
Gas fluxes were calculated from the rate of change of N2O concentration in
the chamber headspace, determined by linear regression based on the four samples
(Verchot et al. 1999). The slope of the best linear fit is expressed in mass units
per space by using the ide al gas law:
N2O (µ N2O m-2 h-1) = N2O x Pressure x 28 x Chamber height
Air temp x Gas Constant
7
Where N2O is rate of N2O concentration in ppm N2O m-2 h-1 in the chamber
headspace, pressure is air pressure in pascal (Pa), 28 g mole-1 is the mass of N (14
g 2) per mole of N2O, chamber height is in meter, air temperature is in Kelvin
(273+°C), gas contant is 8.31441 j k-1 mol-1.
Nitrogen Availability
Laboratory incubations were carried out to measure the rates of net
mineralization and net nitrification. Soil samples were collected on February
2013. One soil sample per chamber collected within 0-10 cm depth. Samples
transported to the laboratory and refrigerated until incubation. The coarse roots
and organic matter detritus was manually removed from the soil samples. The
procedure described by Hart et al. (1994) was used to determine net
mineralization and net nitrification. A 10-g soil subsample was extracted in 100
ml of 2M KCl to determine inorganic N concentrations. These extracts were
shaken for an hour with magnetic stirrer and settled for 24 hours. A 20-mL
aliquot of the supernatant was removed, filtered through a grade no.42 whatmann
filter paper and frozen for later analysis. NH4+ analysis was done on auto analyzer
from Bran LuebbeTM using colorimetric method with indophenols blue (Solorzano
1969). Determination of NO3- was done on U-2001 spectrophotometer from
Hitachi using brucine procedure (EPA 1971). A second subsample of 10 g was
incubated in the dark at room temperature (25-28°C) for 10 days. After 10 days,
the incubated sample was extracted according to the procedures described above
The net N mineralization rate was calculated as the change in NH4+ + NO3concentration during the 10 day incubation. Net nitrification rate was calculated
as the difference between initial and final NO3- concentrations.
Data Analysis
Statistical analysis was done with SPSS software v.19. The data set showed
a non-normal distribution (Shapiro-Wilk test). A log transformation of the data set
was performed as an attempt to fix the distribution but gave unsatisfactory result.
Thus differences in N2O emission among N doses determined using non
parametric analysis (Kruskal Wallis Test). Simple regression analyses were
carried out to examine relationships between N2O emission and environmental
variables.
8
4 RESULT AND DISCUSSION
Result
Climatic observation
During our study period, there was no clear distinction between dry and
wet season. Rainfall was highest in December 2012 (354 mm) and lowest in
January 2013 (36.42 mm). Flux data were collected in the field around 9 am to 2
pm. Thus, every month we rotated the measurement time for each plot in order to
capture the variability. Air temperature fluctuated throughout the measurements
from 24.6°C to 49.6°C with high relative humidity. While air temperature
fluctuates during the day, mean of soil temperature remains stable at around 28°C.
The first fertilization treatment was conducted on 23 October 2012. We observed
no rain event on the fertilization day and 2 days after fertilization (0 mm). In
opposite, the second fertilization on 18 April 2013 was done during rainy season
where rainfalls continuously occurred one week after fertilization.
-1
Rainfall (mm month )
400
(a)
300
200
100
(b)
Air Temp (°C)
0
46
44
42
40
38
36
34
32
30
30
Soil Temp (°C)
(c)
29
28
27
26
Oct
Nov
Dec
Jan
Feb
Mar
Figure 2 Monthly rainfall (a), air temperature (b) and soil temperature (c) in the
top 10 cm of the soil profile for N0 ( ) N1 (
) and N2 (
)
9
Water level (WL) ranges from -36.5 cm to -85.5cm. We cannot measure
WL data on December 2012 when rainfall was the highest. Based on 5 months
observations (23 measurements), there was no clear relationship across WFPS,
mG, mV, WL and rainfall. We observed weak relationship also between mV and
WFPS.
Table 2 Water level (WL), gravimetric water content (mG), volumetric water
content (mV) and WFPS during study period
Month
WL
mG
mV
WFPS
(-cm)
(g g-1 d.w.)
(m3 m-3 d.w)
(%)
59.29 (0.87)c
65.14 (1.04)b
October
2.48(0.01)bc 0.44(0.01)ab
0.51(0.01)c
59.94 (0.74)c
November 56.80 (0.55)a
1.22(0.07)a
n.a
54.62 (3.01)bc
n.a
December
2.02(0.11)b
0.48 (0.02)bc
56.64 (2.60)c
62.17 (0.31)ab 1.23(0.04)a
January
n.a
31.67 (2.60)a
62.33 (0.93)ab 1.17(0.10)a
February
0.40 (0.02)a
46.69(2.70)b
58.00 (3.63)a
March
2.94(0.03)c
Values are mean ± standard error (in parenthesis)
Means with the same letter are not significantly different
n.a. is not available due to missing data.
Nitrogen Availability
Inorganic N pools were dominated by NH4+ in all N treatments (Table 3).
Soil sampling was conducted on February. Soil NH4-N concentration at N0, N1,
N2 varied from 19.94 to 188.32, 47 to 290.42, 2.49 to 42.72, respectively. We
observed some high NH4+ concentrations at N1 and as expected it came from the
CP zone. NO3-N concentration at N0,N1,N2 ranged from 0.08 to 18.45, 0.19 to
14.93, 0.46 to 15.28 respectively. In summary, we observed higher N availability
at N0, N1 than that of N2 treatment. We found significant different among N
treatments for NH4+ (P=0.0002). However there were no significant found on
NO3-, net mineralization and net nitrification among the N treatments (P=0.77,
P=0.25, P=0.05 respectively). The result of net mineralization showed majority
positive value which indicate no NO3- loss during incubation.
Table 3 Ammonium, Nitrate, Net Mineralization and Nitrification for the
different N treatment
Treatment
N- NH4+, N- NO3-,
mg N kg-1 mg N kg-1
d.w.
d.w.
Net
Mineralization
(mg N kg-1 d-1)
89.39b
6.03a
4.73a
N0
114.65b
5.59a
5.94a
N1
17.73a
5.40a
2.62a
N2
Means with the same letter are not significantly different
Net
Nitrification
(mg N kg-1 d-1)
0.89a
0.83a
0.24a
10
3.3
N2O Fluxes
We observed majority positive fluxes (85%) during the 6 months
measurement. N2O fluxes from the soil showed seasonal fluctuation. Fluxes data
were most negative and low during drier days in particular on 23 and 25 October
and high relatively high in December. We observed low emissions in March
despite the high monthly rainfall due low rainfall during measurement and two
days before measurement. Few negative fluxes were also recorded during the
relatively wet days. Monthly fluxes were calculated from the average of ten
chambers (n=10) for each plot except for October and November when we
conducted intensive sampling of 9 (n=90) and 11 (n=110) days respectively. This
is to ensure a robust calculation that avoid under or over estimation. N2O
Emissions remain low on October at the fertilization plot (N1 and N2). It
increased on November and December following the rain events with a similar
magnitude for all N treatments and control. Emission relatively similar on
January, February and March. We observed high variability of fluxes on
December for all N treatments.
N 2O Flux (g N-N 2O ha-1 d-1)
350
300
250
200
150
100
50
0
Oct
Nov
Dec
Jan
Feb
Mar
Figure 3 Monthly fluxes (g N ha-1 d-1) of N0( ),N1 ( ),N2( )
in the oil palm plantation, Jambi, Sumatra, Indonesia
3.4
Intensive Sampling
We examined the dynamic and magnitude of N2O emission after
fertilization through an intensive samplings on October and November. We
observed increasing N2O fluxes 10 days after fertilization in all N treatments
following the rain events. Emission peak was noticed 19 days after fertilization
but didn’t seem to be related to the N application. We found CP was higher than
FP at N1 treatment 19 days after fertilization, however they were not significantly
different. We also observed higher CP fluxes than that of FP at N2 treatment in
11
day 2 and 3 after fertilization. Overall, we didn’t see the effect of fertilizer in both
N1 and N2 treatment.
(N0)
N2O (g N-N2O ha-1 d-1)
250
200
150
100
50
0
(N1)
N2O (g N-N2O ha-1 d-1)
300
250
200
150
100
50
0
(N2)
N2O (g N-N2O ha-1 d-1)
250
200
150
100
50
0
-1 0 1 2 4 5 6 7 9 11 13 15 17 19 21 23 25 27 29
Days after fertilization
Figure 4 N2O Fluxes (mean ± SE) of CP (
), FP (
during intensive sampling (d-1 to d+29)
3.5
) for N0, N1 and N2
N2O Fluxes and its controlling factor
We observed maximum fluxes were occurred when water level (WL) was
around -60 cm. Fluxes seem to decrease when WL lower than -60cm. N2O
emission were maximum at WFPS around 60-80 %. Fluxes also maximum when
soil temperatures were 28-29 ºC. Fluxes were decreasing when temperature above
30 ºC. We found significant relationship across all measured environmental
factors, however R2 was really low. Gravimetric and volumetric water content
were significantly related to water level (P=0.01 R2=0.006, P