Effect of enhanced biochar on green house gas emission and paddy rice yield from loamy
sand soil after first year trial in Thai Nguyen, Viet Nam
Lan Anh Mai Thi1, Stephen Joseph2,3; Lukas Van Zwieten2; Kien Hoang Trung1;
Genxing Pan3, L Li3; Trinh Mai Van4
(Corresponding authors: Lan Anh Mai Thi, mailananh.festn@gmail.com)
Abstract:
Rice fields are considered as important sources of CH4 and N2O emissions. Organic
matters and water regimes are the determining factors for CH4 and N2O emissions from rice
fields. Rice on the upland areas of Vietnam is mostly planted on the soils which are acidic and
have low organic matter. Biochar could increase the pH and the organic carbon content of the
soil as well as increasing yields if combined either with compost or with chemical fertilizer. This
study investigates the effect of biochar as well as biochar-composting on the green house gas
emission and rice yield on paddy fields that have a sandy clay loam, in suburb of Thai Nguyen
City, Vietnam (21o34’275’’ North, 105o46’ East). This paper reports on the results of the first
year of a three year field trial. Experimental treatments include: T1: no amendment (control);
T2: application of inorganic fertilizer (NPK); T3: NPK+ 1.5 tonnes biochar; T4: NPK+ 10
tonnes of composted buffalo manure without biochar; T5: NPK+ 10 tonnes of composted of
buffalo manure/5% biochar mixture. A composite high nutrient biochar was produced by
blending buffalo dung, Hybrid Acacia wood, bamboo, rice husk, rice straw. All feed stocks were
coated with a mixture of 5% of buffalo dung, 2% of lime; 10% clay; 5% of rice straw ash to
increase the mineral content on the biochar’s surface. The mixture of minerals and biomass (rice
straw and timber wood) were dried and then pyrolysis in TLUD - drum oven at 400-500oC to
produce the biochar. After year trial of experiment, the utilization of organic amendments
increased the amount of SOC compared with the control soil. The highest soil carbon content
and nitrogen content was observed in treatment of compost mixed with 5% biochar. The highest
yield increase was from treatment NPK+ 1.5 tonnes biochar.
There was significant differences in methane emission flux (p<0.05) between plots which
was added 10 tonnes of compost with 5% biochar plus NPK and 3 other treatments. There is no
difference in CH4-C flux in treatment T2 (NPK) and T3 (NPK+1.5t/ha biochar) and T4 (10 tonne
compost without biochar plus NPK). There was not significant difference (p> 0.05) between the
CO2e GWP (changed from 134.4-175.6g/h/WRGS) and no significant difference in N2O -N
(changed from 916.5 - 1115.4 µg/h/WRGS between 4 treatments.
Key words: Soil organic carbon, rice, biochar, compost,
1
Thai Nguyen College of Sciences, Thai Nguyen, Vietnam
School of Materials Science and Engineering, University of New South Wales, SYDNEY, NSW2052
Australia
3
Institute of Resources, Ecosystem and Environment of Agriculture, Nanjing Agricultural University,
Nanjing, 210095, P.R.C.
4
Institute for Agricultural Environment (IAE), Ha Noi, Viet Nam
2
1
1. Introduction
Methane (CH4) and nitrous oxide (N2O) are greenhouse gases (GHGs) with important
impacts on our environment. Increasing atmospheric N2O concentration may also be detrimental
to the stratospheric ozone layer. The concentrations of CH4 and N2O are lower than carbon
dioxide (CO2), but their global warming potential are 25 and 298 times as strong as that of CO2
respectively ((Forster, 2007)). The concentration of CH4 was increased by 4.9ppb/yr and N2O
was increased by 0.8± 0.2ppb/yr (IPCC, 2001). Agricultural soil is a major source of CH4 and
N2O.
Converting crop residues to biochar through thermal decomposition (pyrolysis) is a
potential solution for minimizing emissions and maximizing the recycling of nutrients. Biochar
is a carbon-rich solid material produced by heating biomass in an oxygen-limited environment
and is intended to be added to soils as a means to sequester carbon (C) and maintain or improve
soil functions (Joseph, 2010). Many studies have now been undertaken to determine the affects
of adding biochars with or without chemical fertilizers and/or compost to different soils and to
different crops. In many cases there has been an increase in crop yields and soil properties
including an increase in the recalcitrant carbon content and reduction of greenhouse gas
emissions (Lehmann et al. 2003b; Yamato et al. 2006; Chanetal. 2007, 2008; Steiner et al. 2007;
Kimetu et al. 2008; Hidetoshi et al. 2009; Yeboah et al, 2009; Gaskinetal. 2010; Major et al.
2010; Van Zwieten et al. 2010a, b). An important aspect for improving crop growth in highly
weathered soils is the liming effect of biochars that typically have a high pH (Yamato et al. 2006;
Van Zwieten et al. 2010a; Yuan and Xu 2011) and the increase in cation exchange capacity
(CEC) (Liang et al. 2006) to reduce nutrient leaching (Lehmann et al. 2003b). Initial field trials
using biochar manufactured in a simple drum pyrolysis kiln was carried out SFRI (Hien & Vinh,
2012) in the districts of Dinh Hoa and Ba Thuoc in 2 poor provinces of Thai Nguyen and Thanh
Hoa. Results indicated that there was a significant increase in rice yields (20-30%) when
500kg/ha of biochar and 9.5tonnes/ha of composted manure and NPK or when 2.5tonnes/ha of
biochar and NPK when were added to the soil (Hien & Vinh, 2012).
The recent trials were undertaken to determine if similar yield increases could be
achieved in a different pedogenic climate around the city of Thai Nguyen. The specific
objectives of the trials were to
(1) Quantify the effects of charcoal, organic, and inorganic fertilization on soil fertility and crop
production; and
(2) Evaluate the sustainability of charcoal additions in terms of maintaining high-SOM contents
and nutrient availability in loamy sand.
(3) Methane and nitrogen oxide emission monitoring from the field under paddy rice soil
condition.
The hypothesis that was to be tested is “charcoal additions improve nutrient availability
and reduce GHG emission; that crop productivity is maintained on a higher level than without
charcoal addition”.
2. Materials and methods
2.1. Materials: Pretreated feedstock and production of biochar
Bamboo and wood (which was soaked in pond for a year) were dried and added in equal
2
proportions to dry rice husk and rice straw. To increase available nutrients and the CEC of the
biochar a slurry consisting of 2% lime, 10% clay and 5% of buffalo manure and 5% rice straw
ash was added to these feedstocks. The mineral coated biomass was dried and then pyrolysed in
a drum oven (Care International in Viet Nam, 2012) at 450-600oC over a period of 1.5-2 hours.
2.2. Making compost with biochar and without biochar for experiments
The composting method used was developed by SFRI and consisted of adding by weight
5% biochar 1% compost enhancing plant (Eupatorium odoratum L.), 0.5kg of microorganism
package per 1 tone of manure. The procedure was as follows:
1. A layer of 10-15 cm of buffalo was placed on the ground approximately 2m in diameter.
2. Approximately 100g of the micro-organisms was added to buffalo dung.
3. Approximately 25% of the biochar was sprinkled over the dung
4. Green leaf was then added on top of the biochar in thin layer, to cover all manure.
5. A further 3 Layers of dung/biochar and green leaves were added.
6. Then cover compost pile with nylon that has approximately 30 small holes (10 mm in
diameter) for water vapor to escape.
Manure, green plant and microorganism are added for composting without biochar using
the same procedure as above. Composting is complete after 45 days in spring season.
2.3. Method
2.3.1. Soil and Field trials
Characterization of soil at study site
This study was implemented in Thai Nguyen city, Thai Nguyen province, Viet Nam.
Longitude is 21o34 275’ North; 105o46 796’ East. Rice has been cultivated in this field for at
least 20 years. Soil samples were taken at the depth of 0-20cm. The soil was loamy sand with a
particle size distribution of 79.8%, 11.3%, and 8.9% respectively of sand, silt, and clay. Bulk
density is 1.34g/cm3. The properties of the soil are given in table 1. The pHKCl (1:5) is acidic at
4.43. Cation Exchange Capacity (CEC) in research areas is 12.3cmol/kg, soil organic carbon
(SOC) 0.96%, total nitrogen (0.11%), total phosphate (P) is 0.017% and total potassium (K) is
0.03%. CEC, P and N are typical of soils in this area but OC and K are low. Burning of the rice
straw causes volatilization of its K content and this in part could result in a low K in the soil after
experiment.
Table 1. Soil properties in experiment
pH (1:5)
H2O
6.27
KCl
4.43
CEC
(cmol/kg)
OC
12.3
0.96
N
P
K
Total content (%)
0.11 0.02 0.03
Fe
0.22
Available Exchange
P
K
(ppm)
22.2
22.2
Field trial:
Field trial was set up as random complete block design (5m x 6m) with 5 treatments with
3 replicates as below: T1: Control with no amendment; T2: NPK; T3: NPK + 1.5 tonne biochar;
T4: NPK+ 10t/ha compost buffalo manure without biochar (CP); T5: NPK + 10 tonne/ha of
compost with 5% of biochar (CPBC). Chemical fertilizer was applied at 100kg N, 90kg P 2O5, 60
3
kg K2O per ha. The amount of NPK was the same in all treatment, except Control where no
ammendent or fertilizer was added.
2.3.2. Sample analysis
Biochar analysis
Biochar pH values were obtained in duplicate using a ratio of 1.0 g of biochar in 20 mL
deionized water with the modification that the time on the shaker was increased to 1.5 h to
ensure sufficient equilibration between solution and biochar surfaces (Rajkovich et al., 2011).
Potential CEC was determined by saturating 1.0 g of the biochar with 40 mL of CH3COONH4
1N at pH 7 and placing on a table shaker overnight. The shaking ensured sufficient wetting of the
biochar surfaces. After shaking, the initial 40 mL of 1N ammonium acetate was extracted by
vacuum with an automatic extractor, and a second addition of 40 mL ammonium acetate was
added. The samples were then washed with ethanol three times with a total volume of 60 mL and
then received 40 mL of 2N KCl. This initial 40mL addition of 2 N KCl was allowed to stand 16h
to ensure adequate time for replacement of the absorbed NH4+ cations. The initial 40 mL was
extracted and then immediately followed by a second addition of 40 mL of 2N KCl and
subsequent extraction. The 10 ml extracted NH4 solution was quantified by Kjeldahl method
(Rajkovich et al., 2011).
Total C and N were measured by Dumas combustion using an Elementar vario MAX CN
analyzer with combustion chamber set at 900°C and oxygen flow rate of 125 mL min−1 (Zwieten,
Kimber, & Morris, 2010). Total P, Ca, Mg, and K was analyzed using the following method. The
biochar samples were combusted at the temperature of 500°C over 2h and then the oven was
maintained at 500°C for 8h. 5.0 mL concentrate HNO3 was added to each sample and digested at
120°C until all liquid was evaporated. Secondly, tubes were removed and allowed to cool before
adding 1.0 mL HNO3 and 4.0 mL H2O2. Then, the samples were placed back into a preheated
block and cooked at 120°C to dryness. The dry sample was dissolved with 1.43 mL HNO3, made
up with 18.57 mL demonized water to get the 5% acid concentration, sonicated for 10 min, and
filtered.
Taking green house gas sample
Closed chamber technique was used to collect the gas samples (Pathak et al., 2001;
Zhang et al., 2010). There were two parts of the chamber. One part was the base chamber fixed
permanently in the soil throughout the rice growing season, and second part was top replaceable
chamber Fig. 5b. The base chamber was made up of stainless steel with 40 cm length, 36 cm
width and 35 cm height. Before transplanting, the base chamber was fixed in the middle of each
plot by inserting 10 cm of its base into the soil. The base chamber contained grove on the top
edge so as to fix top chamber during gas sampling. Furthermore, the base chamber was provided
with two holes on the opposite sides near the level of the soil so as to allow the flow of water in
and out of the base chamber. The holes were sealed with rubber cork during gas sampling to
avoid the air leakage. Four hills of the rice plants were maintained within the base chamber. In
addition, wooden boardwalk was provided to reach each base chamber to avoid the soil
disturbance during sampling. The top chamber was 2 types. The small chamber was used for
sample taking at 35 DAT and 50 DAT. The small one made up of Plexiglas with aluminum
frame with 36 cm width, 40 cm length and 37.5 cm height. The big was used for 3 times latter.
The big one made up of Plexiglas with aluminum frame with 36 cm width, 40 cm length and 95
4
cm height. Two opposite sides of the top chamber were transparent and the other two sides were
non-transparent. The non-transparent sides of the chamber were faced towards the sun during gas
sampling to avoid direct sunlight into the chamber. The reason behind this was to reduce the
temperature fluctuation inside the chamber during its deployment. A thermometer to measure
temperature and two small electric fans to homogenize air during gas sampling were fixed inside
the top chamber. Four fans were connected with disposable batteries placed on the top of the
chamber to supply power. The top chamber also contained a 3 mm hole on the top. A open ended
plastic tube with 5 mm diameter and 50 m length was inserted into the chamber through the hole
with one end hanging 10 cm inside and the other end protruding 40 cm outside the top chamber.
The hole was sealed from the periphery after the tube insertion so as to prevent air leakage. A
check valve was provided on the protruding part of the tube to control the gas flow during gas
sampling.
To determine seasonal emissions of CH4 and N2O, gases samples were collected 5 times
on 35 DAT (maximum tiller); 50 DAT (Booting); 63 DTA (Flowering); 80 DAT (Milky Ripen)
and 90 DAT (Total ripen). Gas sampling was started from the first replicate of each treatment at
9.00 h followed by second replicate at 9.45 h, and third replicate at 10.30 h in a row during each
sampling day. Sampling time was decided based on the procedure recommended by various
previous studies (Buendia et al., 1997; Zou et al., 2005). While sifting from one replicate to
another 15 minutes time difference was maintained so as to let the air inside the top chamber to
normalize.
During gas sampling the top chamber was placed on the grove of the base chamber and
water was poured into the grove so as to avoid ga leakage. The whole assemble was made an
airtight chamber during gas sampling. Four fans inside the chamber were operated immediately
after placing the top chamber on the base chamber. In total, the top chamber was deployed on the
base chamber for 30 minute during each gas sampling. Gas samples; t0, t1, t2 and t3 were
collected at 0 minute, 10 minutes, 20 minutes and 30 minutes after the deployment, respectively.
A 60 ml syringe provided with a needle was used to pull the gas samples from the chamber. The
needle with the syringe was inserted into the tube, the check valve was opened and the tube was
flushed with the air inside the chamber for five times before pulling out the gas samples so as to
take representative samples. Exactly 50 ml gas was pulled into the syringe and the check valve
was closed before the syringe was pulled out from the tube. The pulled gas was immediately
inserted into the pre-evacuated 12 ml vials. The vials were analysis in the Lab of Center of
Biochar & Green Agriculture, Institute of Resource Ecosystem & Environmental of Agriculture,
Nanjing Agricultural University.
Green house gas analysis:
The concentration of CO2, CH4 and N2O in a gas sample was simultaneously analyzed
with a gas chromatograph (Agilent 7890A) equipped with a flame ionization detector
(FID) and an electron capture detector (ECD). N2 was used as the carrier gases and an Ar–
CH4 gas mixture as the make-up gas for ECD analysis of CO2, CH4 and N2O. N2O was
separated by two stainless steel columns (column 1 with 1 m length and 2.2 mm in
diameter, column 2 with 3 m length and 2.2 mm in diameter) that were packed with 80–
100 mesh Porapack Q. N2O was detected by ECD, while CO2 and CH4 was detected by FID.
The oven temperature was controlled at 55 ◦C, and the temperatures of the ECD and
FID were set at 330◦C and 200◦C, respectively.
5
Calculation of amount of flux was based on the change in gas concentrations within the
enclosed headspace with increase in time from 0 min to 30 minute during each sampling. Data
points were excluded unless the change in concentration of gas from t0 – t30 yielded linear
regression value, i.e. r2 greater than 0.80 with increase in time from 0 min to 30 minutes.
Following equation (Pihlatie et al., 2013) was used to calculate the hourly flux (F= mg m-2 h-1) of
CH4 and N2O:
𝑴 𝑽
𝟐𝟕𝟑. 𝟏𝟔
𝑺 𝑽𝒎 𝒙 𝑨 𝒙
𝒙𝟑𝟔𝟎𝟎
(𝑻 + 𝟐𝟕𝟑. 𝟏𝟔)
𝑭=
𝟏𝟎𝟎𝟎
Where,
• F is the final flux value of gas of interest at the time of chamber closure and is expressed as mg
m-2 h-1,
• S is the slope or time derivative of the linear fit at chamber closure and is expressed as ppm s-1
• M is molecular mass of the particular gas, which is 16.042 g mol-1 and 44.0128 g mol-1 for
CH4 and N2O, respectively
• Vm is ideal gas mole volume, which is 0.0224 m3mol-1
• V is the volume of chamber above water/soil level and is expressed as m3,
• A is the surface area of soil covered by the base chamber and is expressed as m2,
• T is the temperature reading in the thermometer, which was installed inside the chamber and is
expressed as 0C.
The CO2 equivalent (CO2-e) global warming potential (GWP) over 100 years time
horizon for each of the treatment over the WRGS were calculated using the IPCC GWP factors
for CH4 and N2O. The IPCC GWP factors on mass basis for CH4 and N2O is 25 and 298 times
CO2 over 100-years time horizon, respectively (Forster et al., 2007). The CO2 emissions from the
rice field under any of the treatments were not included during the calculation of total CO 2-e
GWP. The CO2-e GWP ton-1 of rice production from each of the treatment was also calculated
on the basis of total CO2-e GWP.
Following equations were used to calculate the total CO2-e GWP kg ha-1 and CO2-e
GWP per unit of rice grain yield for each of the treatment:
Total CO2e GWP (CH4+N2O) = 25 x total cumulate CH4+298 x total cumulate N2O
CO2e GWP tonne-1 of rice grain produced =
𝑇𝑜𝑡𝑎𝑙 𝐶𝑂2𝑒 𝐺𝑊𝑃
𝑅𝑖𝑐𝑒 𝑔𝑟𝑎𝑖𝑛 𝑦𝑖𝑒𝑙𝑑 𝑖𝑛 𝑡𝑜𝑛𝑛𝑒
Soil analysis:
Soil pHKCl was extracted by KCl 1N (1/5 w/v) and the pH measurement taken. Soil
organic carbon (OC) is analyzed using the Walkley and Black method (Walkley & Black., 1934).
The soil organic matter is oxidised by dichromate (Cr2O72-) and concentrated sulphuric acid.
Unreduced dichromate is titrated with ferrous ammonium sulphate using diphenylamine as a
redox indicator. Total N was digested by concentrated H2SO4 and then determined by Kjeldahl
method. Total P was extracted by mixed concentrated H2SO4 and HNO3, measured on color
specphotometer at = 882 nm. Total K was digested by concentrated HNO3 acid and measured
on flame photometer (BWB XP). To measure available P– Bray 2, available K, exchangeable
Ca2+, Mg2+ and CEC extraction was carried out using ammonium acetate solution (1M, pH7).
6
Ca2+ and Mg2+ concentration was measured on AAS. CEC was measured by steam ammonium
distillation with semi- micro Kjendahl, then titration, (TCVN Manual, 2010).
3. Results and discussion
3.1. Some characterizations of biochar
The properties of the biochar used in the trials are provided in table 1. Enhanced biochar
made from mixed biomass have high nutrient content of total carbon (54%); nitrogen (0.82%) as
well as Calcium, Magnesium, potassium, phosphorus. Mixture with rich of mineral and clay
could help t improved CEC of biochar (13.6 cmol/kg)
Table 2. Biochar properties for field trial in experiment spring 2013
pH H2O
(1:4)
9.78
CEC
cmol/kg
13.6
C
N
C/N
P
0.82
65.9
5.12
%
54
K
Ca Mg
g/kg
25.87 13.8 3.9
Enhanced biochars after composting have higher total carbon (24%) and total nitrogen
(19.4%) then before composting. Composted manure with 5% biochar has higher total carbon
and total nitrogen content. These results showed the improvement of making compost with the
addition of 5% biochar can help to increase nutrient content of amendment.
Figure 1. Total carbon and total nitrogen of biochar; compost manure before and after
composting.
Analyses of enhanced biochars made in TLUD have shown that the clay, lime and some
of the nutrients from the manure resides in the macrospores of the biochar. It is probably that
these nutrients are plant available. Figure 1 is a piece of biochar that has been mounted in resin
and polished. Analysis of the light colored mineral phases by energy dispersive x-ray
spectroscopy (EDS) shows that these mineral phases are high in K, Ca, Si and Al. The K and Si
probably originate in part from the added rice straw ash and the Ca from the lime (figure 2).
3.2. The effect of organic matter amendment on rice yield
Results of these first year trials show that there is a significant increase in yield of 45% in
spring season and 74% in summer season when 1.5tonnes/ha of biochar was added to the NPK
fertilizer compare to the addition of only NPK (table 3). Although, in flowering stage of whole
7
rice growth season (WRGS), rice was affected by a big storm; the summer rice yield was lower
than spring season, plots of 1.5 tonnes/ha of biochar plus NPK till got highest yield.
There was a small increase in yield when CP and CPBC compared with the addition of straight
NPK but this was significantly smaller than the addition of biochar plus NPK. All treatments
resulted in significantly greater yields than the treatment that had no fertilizer and/or amendment.
There was no significant difference between CP and CPBC.
There was not significant difference between the number of filled grains per panicle
(changed from 117.2 – 130.4 filled grains/panicle), weigh of 1000 filled grains (range between
18.15 – 19.54 gram in spring season; 17.4-19.0 gram in summer season), rate of filled grain per
all grain in the panicle (90.3– 92.9% in spring season and from 70.3-80.03% in summer season)
for all of the treatments.
Figure 2. Examination of the biochar using SEM with EDS detector
However, there was significant difference in number of panicles per hill between NPK plus 10
tonnes of CP (5.2 panicle per hill) and 10 tons of CPBC with NPK (7.5 panicle per hill). There
were not significant differences between the numbers of panicles/hill for the other treatments.
There was a significant difference in the average height of rice plants between the CPBC and the
other amendments (Table 3).
8
Table 3. Rice yield in spring season 2013
Weight of 1000
grains (g)
SP13
SM13
18.15a
17.8a
19.54a
17.4a
Actual Yield
(tonne/ha)
SP13
SM13
5.1a
2.2a
6.4b
2.71ab
Theorical Yield
(tonne/ha)
SP13
SM13
6.22a
7.08a
7.2ab
6.69a
Filled grain/
Panicle (%)
SP13
SM13
88.0a
70.3a
90.3a
71.6a
18.2a
19.0a
7.4c
3.82c
5.16a
10.06b
92.6a
74.3a
18.24a
18a
6.8bc
3.0ab
7.14ab
7.95a
92.5a
74.0a
19.5a
18.6a
6.7bc
3.29ab
9.25b
8.51a
91a
80.0a
CV,%
8.0
6.2
8.5
9.0
18.5
20.3
7.1
4.4
LSD, 5%
2.83
2.12
1.02
1.18
2.46
3.08
7.5
9.9
Treatments
Control
NPK
1.5 tonne BC +
NPK
10 tonne
compost without
BC + NPK
10 tonne
compost with
5% BC + NPK
Notes: SP13: spring season 2013; SM13: Summer season 2013.
3.3. Soil characterize before and after first trials.
After first season trial, there was no change in pHH2O (1:5) and pHKCl (1:5), with
variations between 6.11- 6.82 and 4.27– 4.49. There was a significant difference between the
treatment NPK plus 1.5 tonnes of BC and all of the other treatments.
The CEC of the soil (table 4) where organic amendments were added (CP and CPBC)
was significantly higher than CEC of soil in the control, NPK and NPK plus 1.5 tonnes BC plots.
After first season, CEC in soil of treatments with added CP and CPBC was significantly higher
than CEC in soil before trials. SOC and total nitrogen in soil after the trial was higher than before
trials started however there was no significant different in soil organic carbon in the first trial
between the 5 treatments. SOC had increased from 0.96%, to between 1.23-1.56%. Total
nitrogen had increased slightly from 0.11% before starting the trial to between 0.117 – 0.136%.
Total nitrogen was highest in 1.5 tonnes of BC plus NPK treatment.
SOC and N in soil increased with application of all of the amendments. Total SOC is
highest in treatments with 10t/ha compost without or with biochar (T4 and T5) although this is
not significant. There is no difference in SOC content in the soils that had treatment T2 (NPK)
and T3 (NPK+1.5t/ha biochar).
There was a significant increase in total P after the addition of all amendments except for
the addition of NPK. However there was a decrease in available P after harvesting the rice for
all of the treatments with the lowest available P in the plot that had no amendment. There was a
significant decrease in total and available K for all of the amendments. The data indicates that
these amendments increased nutrient uptake by the plants.
9
Table 4. Soil properties before and after 1 year application of biochar and compost
pH (1:5)
Before
experiment
T1
T2
T3
T4
T5
CV,%
LSD
5%
CEC
(cmol
/kg)
OC
N
pHH2O
pHKCl
6.27
4.43
12.3
0.96
0.11
6.11a
6.46a
6.61a
6.82a
6.48a
6.7
4.4ab
4.42b
4.27a
4.49b
4.49b
1.6
11.6a
11.5a
12.2a
14.6b
14.5b
5.6
1.32a
1.23a
1.35a
1.44a
1.56a
11.8
0.117a
0.120a
0.136a
0.124a
0.122a
12.9
0.8
0.13
1.38
0.30
0.03
P2O5
K2O
Total content (%)
0.017
P2O5
K2O
Available (ppm)
0.03
0.071c 0.01a
0.001a 0.012ab
0.05b 0.011ab
0.05b 0.011ab
0.072c 0.014b
19.7
17.5
0.02
N
0.004
32.6
22.2
22.16
32.9a
33.8a
25.9a
45.9a
36a
55.7
7.85a
10.3a
12.2a
11.8a
10.9a
43.2
7.9a
9.7ab
8.8ab
9.6ab
11.5b
16.2
35.7
0.4
1.15
Notes: T1: no amendment (control); T2: application of inorganic fertilizer (NPK); T3: NPK+
1.5 tonnes biochar; T4: NPK+ 10 tonnes of composted buffalo manure without biochar; T5:
NPK+ 10 tonnes of composted of buffalo manure/5% biochar mixture.
3.4. Changes in SOC in the top soils
Changes in SOC from the beginning of the experiment to harvesting of the rice in the first
spring season 2013 are presented in figure 3.
Figure 3. Changes in SOC during the trials
There was a very large increase in SOC for all of the treatments 36 days after their
incorporation in the soil. The largest increase was measured in the plots where NPK and
10
compost with biochar were added. SOC in the control and NPK plots increased due to the
incorporation of crop residues from the previous season and from irrigation water that had a high
organic matter. After 36 days SOC was highest in T5 plots and then reduce slowly across rice
growing period.
After day 36, there was no significant difference (p>0.05) in the changes in SOC for
treatment T1-T4 plots (1.3– 1.6%) between the 4 growth stages before harvesting. For NPK plus
1.5 tonne/ha of biochar and 10 tonnes/ha of compost without biochar, SOC was highest at
Panicle stage (45 days after transplanting the rice seedlings). Treatment with NPK+10 tonnes
compost mixed with 5% biochar gave the greatest increase of SOC. After first season, SOC was
increased by 62.5% with organic amendments but there was a decrease with the application of
NPK although this was not significant.
3.5. Green house gases by adding organic matter in four treatments.
3.5.1. Green house gases emission form paddy rice
The green house gases emission from loamy sand soil in paddy rice cultivation is
provided in figure 4.
Figure 4. Green house gases emission form paddy rice in spring season 2013
There was significant differences in methane emission flux (p<0.05) between plots which
was added 10 tonnes of compost with 5% biochar plus NPK and 3 other treatments (NPK; 1.5
tonne biochar + NPK and 10 tonne of compost without biochar + NPK). CH4 flux was lowest in
treatments with 10t/ha compost with biochar (T5), 5.36 CH4-C g/m2/WRGS. There is no
difference in CH4-C flux in treatment T2 (NPK) and T3 (NPK+1.5t/ha biochar) and T4 (10 tonne
compost without biochar plus NPK).
There was not significant difference (p> 0.05) between the CO2e GWP (changed from
134.4-175.6g/h/WRGS) and no significant difference in N2O -N (changed from 916.5 - 1115.4
µg/h/WRGS between 4 treatments.
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Figure 5. Green house gases emission form paddy rice in spring season 2013
3.5.2. Correlation of soil organic carbon (%) and methane emission
Methane emission in WRGS was showed in figure 6. CH4 flux was highest in max tiller
stage (4.04-4.57 mg/h/m2). At that time, the soil was kept flooded all time to provide enough
water for tiller. CH4 flux was lowest in total ripen stage (0.05-0.22 mg/h/m2) because there was
no water in the field, thus resulting in an increase in Eh with sufficient O2 to oxidize the
methane. Main GHG fluxes at that time were CO2 and N2O.
Figure 6. Methane emission form paddy rice in WRGS in spring season 2013.
Figure 7 - 10 shows the correlation of soil organic carbon in soil and methane emission
after the first experiment. There is no significant correlation between OC and methane emissions.
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Figure 7. Correlation of OC (%) and Methane
emission in plot T2 (NPK application only)
Figure 8. Correlation of OC (%) and Methane
emission in plot T3 (1.5 tonne of biochar + NPK)
Figure 9. Correlation of OC (%) and methane
emission in plot T4 (10 tonnes compost without
biochar + NPK)
Figure 10. Correlation of OC (%) and methane
emission in plot T5 (10 tonne compost with 5% of
biochar + NPK)
3.5.3. Estimation of CO2 equivalent global warming potential for each of the treatment
Table 5 showed the CO2 equivalent global warming potential for each of the treatment.
The first experiment indicated that no significant different in total CO2e GWP and CO2e GWP
per tonne of rice grain in each treatments. There are necessary to have more research and
monitoring on CO2e potential in future.
Table 5. CO2 equivalent global warming potential for each of the treatment
NPK
BC+NPK
CP
CP+BC
CV,%
LSD, 5%
CO2e
(g/ha/Season)
1633.8a
1755.9a
1659.9a
1344a
28.2
899.5
Yield
(tonnes/ha)
6.4a
7.4b
6.8ab
6.7ab
7.5
1.02
13
CO2e GWP
(g/tonnes rice grain)
221.54a
256.19a
260.64a
202.04a
31
146.2
4. Conclusion and recommendation
4.1. Conclusion
After the first trial in spring season, application of all of the treatments increased rice yield over
the control (26% - 45%). The greatest increase in yield was the application of 1.5tonnes/ha with
NPK fertilizer (45% compared with the control). There was no significant difference (p> 0.05) in
yield between the other treatments.
The application of organic amendments increased the amount of SOC compared with the control
soil. The highest soil carbon content and nitrogen content was observed in treatment of 10 t/ha
compost mixed with 5% biochar.
There was significant differences in methane emission flux (p<0.05) between plots which was
added 10 tonnes of compost with 5% biochar plus NPK and 3 other treatments. There is no
difference in CH4-C flux in treatment T2 (NPK) and T3 (NPK+1.5t/ha biochar) and T4 (10 tonne
compost without biochar plus NPK). There was not significant difference (p> 0.05) between the
CO2e GWP (changed from 134.4-175.6g/h/WRGS) and no significant difference in N2O -N
(changed from 916.5 - 1115.4 µg/h/WRGS between 4 treatments.
4.2. Recommendation
Biochar in conjunction with either NPK or compost and NPK could increase crop yields and soil
quality in the North of Vietnam. Biochar in compost could help reduce GHGs flux from loamy
sandy soil in paddy rice condition. Long term trials need to be undertaken in a range of
ecosystems to determine the benefits of this new technology.
5. References
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Soil Enrichment in the Northern Vietnam Uplands Stove-Biochar Project (pp. 1–23).
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Intergovernmental Panel on Climate Change, (Cambridge University Press, Cambridge,
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Hien, N. Van, & Vinh, N. C. (2012). Component: “Application of biochar for sustainable soil
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Rajkovich, S., Enders, A., Hanley, K., Hyland, C., Zimmerman, A. R., & Lehmann, J. (2011).
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temperate soil. Biology and Fertility of Soils, 48(3), 271–284. doi:10.1007/s00374-0110624-7
Walkley, A., & Black., I. A. (1934). A Examination of a Rapid Methord for determination of
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