Estimation of nitrous oxide, carbon dioxide and methane emissions from selected rice soils in Malaysia using DNDC model
Greenhouse gases (GHG) such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are the main cause of global warming. In Malaysia, all these gases can be assessed through Denitrification and Decomposition (DNDC) model in various agricultural systems. Three soils and agriculture sy...
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| Format: | Thesis |
| Language: | English |
| Published: |
2015
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/67750/1/FP%202015%2083%20IR.pdf |
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| Summary: | Greenhouse gases (GHG) such as carbon dioxide (CO2), methane (CH4) and
nitrous oxide (N2O) are the main cause of global warming. In Malaysia, all
these gases can be assessed through Denitrification and Decomposition
(DNDC) model in various agricultural systems. Three soils and agriculture
system studied for simulation were located in Kota Bharu (Kelantan) situated
between 6°8′N 102°15′E, Alor Setar (Kedah) situated between 06°07'N,l
100°22'E and Selangor, Malaysia situated at 2°43′N 101°57′E. All the three
sites have double cropping system in a year. The objectives of these studies
were to examine and forecast the agricultural practices involved in N2O, CO2
and CH4 emissions from various rice fields and to utilize the modeling
approach to estimate changes in N2O, CO2 and CH4 emissions from rice soils
of Malaysia.
Through DNDC model, four interacting sub-models: thermal/hydraulic, crop
growth, decomposition, and denitrification were simulated. (Rice cultivation is
an important source of GHGs that cause global warming. Rice systems
contribute over 25% of total global anthropogenic CH4 emissions
currently). The model efficiently treats nitrogen inputs from atmospheric
deposition, fertilizer use and nitrogen fixation and represents soil inorganic
turnover to enable calculation of gas emissions. The farmers of Kelantan,
Kedah and Selangor apply 248, 280 and 300 kg N ha-1 year-1,respectively.
The model validation was found satisfactory and gave correct simulations
when compared with other studies reported elsewhere. In Kelantan,simulated CO2 flux rate was 4392 kg C ha-1, 33.7 N2O kg ha-1 year-1 with -2CH4 flux kg ha-1 year-1. The Global Warming Potential (GWP) for CO2 flux
was 16105 kg CO2-eq ha-1, N2O 16403 kg CO2-eq ha-1. However, CH4 was found as sink (-66 kg CO2-eq ha-1). Bulk of all these gases had 32442 kg CO2-eq ha-1 net GWP. In Kedah, the simulated CO2 flux rate was 4675 kg C ha-1 and 15.2 kg N2O ha-1 year-1 recording -3 CH4 flux kg ha-1 year-1. The GWP for CO2 flux was 17141 kg CO2-eq ha-1, N2O 454412 kg CO2-eq ha-1.
However, CH4 was found as sink (-92 kg CO2-eq ha-1) and thus, bulk of all
these gases had 471460 kg CO2-eq ha-1 net GWP. In Selangor, CO2 flux rate
was 1489 kg C ha-1, 152.1 N2O kg ha-1 year-1 with -2 CH4 flux. The GWP for
CO2 flux was 5460 kg CO2-eq ha-1 and N2O 74085 kg CO2-eq ha-1. However,
CH4 was found as sink (-66 kg CO2-eq ha-1). Bulk of all these gases had
79440 kg CO2-eq ha-1 net GWP. The simulations for field uncertainties were
tested with variable nitrogen rates at 20% less than recommended and 20,
40 and 60% more N than recommended along with soil organic carbon
(SOC) rates at 4, 3, 2 and 1.93% kg C kg-1 in Kelantan, 2, 3, 4 and 5% SOC
rates in Kedah and 2.31, 3, 4 and 5% in Selangor. In all the rice sites, the unit
increase in N rate as well as SOC correspondingly increased N2O flux by
10.06, 6.80, 6.51 and 1.16 kg N ha-1. NO flux by 0.76, 3.25, 3.14 and 2.03 kg
N ha-1 year-1.N2 flux 17.87, 18.21, 21.75 and 25.22 kg ha-1 year-1. N2O GWP
flux rate by 3495.3, 1614.6, 6.3.0 and 499.4. In Kedah, the unit increase in N
rate as well as SOC correspondingly increased N2O flux by 0.25, 0.42, 2.51
and 0.96 kg N ha-1, NO flux by 1.04, 1.17, 1.33, 1.51 kg N ha-1 year-1 and N2
flux by 0.12, 0.83, 1.19 and 0.99 kg ha-1 year-1. N2O GWP flux rate by 30.6,
23033, 110302 and 154765. Similarly, in Selangor, the unit increase in N rate
as well as SOC correspondingly increased N2O flux by 2.86, 3.83, 7.61 and
1.95 kg N ha-1. NO flux by 5.41, 5.0, 4.39 and 3.78 kg N ha-1 year-1. N2 flux
by 5.22, 9.76, 18.46 and 30.44 kg ha-1 year-1. N2O GWP flux rate by 1385.3,
1865.3, 2701.5 and 3411.5. In conclusion, the DNDC model validations were
accurate for Malaysian rice. The farmers of these three sites are applying
more nitrogen fertilizer against the crop demand corresponding more yearly
NH3 volatilization loss and increased fluxes of N2O, NO and N2 in the
environment and excess fertilizer leach down in the soil by polluting
underground water. In Malaysian rice, the simulated CH4 values were
negative indicating it as sink. In these sites, the GWP is also increasing due
to elevated CO2, ongoing management practices especially cropping system,
straw incorporation, irrigation/flooding and N fertilizer management as well as
C storage potential of the soil which is increasing with the passage of time
due to left over residues and soil flooding condition.
The DNDC, was modified to enhance its capacity of predicting GHG
emissions from rice ecosystems. The major modifications focused on
simulations of anaerobic biogeochemistry and rice growth as well as
parameterization of rice management. The new model was tested for its
sensitivities to management alternatives and variations in natural conditions
including weather and soil properties. The test results indicated that (1)
varying management practices could substantially affect CO2, CH4, or N2O
emissions from rice; (2) soil properties affected the impacts of management
alternatives on GHG emissions; and (3) the most sensitive management
practices or soil factors varied for different GHGs. For estimating GHG
emissions under certain management conditions at regional scale, the spatial
heterogeneity of soil properties (e.g., texture, SOC content, pH) are the major
source of uncertainty. |
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