IJERD – International Journal of Environmental and Rural Development (2020) 11-1

Research article
erd

Reducing Nitrogen Emission during Cow Manure
Composting with Adding of Rice Husk Biochar
SAVESH MASKEY
Graduate School of Agriculture, Tokyo University of Agriculture, Tokyo, Japan
Email: smaskey27@gmail.com

MACHITO MIHARA*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan
Email: m-mihara@nodai.ac.jp
Received 15 January 2020

Accepted 5 May 2020(*Corresponding Author)

Abstract Nitrogen losses in the forms of ammonia and nitrous oxide emission are major
causes for low nitrogen content in cow manure compost. In addition, nitrogen losses decrease
the agronomic value of compost. In this study, rice husk biochar was added in cow manure
to assess its effects on reducing nitrogen losses. Rice husk biochar is a product ofthermochemical reaction in limited oxygen supply resulting in a product with micro-pores
and large surface area with negative charge. A small scale composting experiment was
designed and conducted using cow manure for a period of 60 days. Gases released were
measured periodically with static gas chamber method. In addition, total nitrogen content andC/N ratio were analyzed. The experiment results showed that the loss of ammonia which isin peak during initial stages were lower in the treatments added with biochar. The cumulativeammonia emission was lowered by 12.6%, 14.5% and 23.2% in 5%, 10% and 15% biochar
added treatments respectively, as compared to control. The cumulative gas flux result of N2O
showed similar trend to that of NH3. N2O emission was lowered by 40.0%, 46.4% and 60.4%
in 5%, 10% and 15% biochar added treatments respectively, as compared to control.
Furthermore, total nitrogen content and C/N ratio had better results in biochar added
treatments. The obtained results may be attributed to the fact that micro-pores and negative
charge in rice husk biochar adsorbed the nitrogenous compounds. Additionally, biochar
increased retention of moisture and nutrients enhancing microbial activity for better
degradation and humification of organic matter. The results indicated that biochar could be agood medium in reducing the nitrogen loss and increasing agronomic value duringcomposting of cow manure.
Keywords cow manure composting, nitrogen emission, rice husk biochar, agronomic value

INTRODUCTION
Composting is a sustainable method for waste management of cow manure. It is a naturally occurring
process where various distinctive microorganisms break down organic matter to produce humus like
substance, which has high agronomic value. On the other hand, composting produces harmful gases
like ammonia (NH3) and nitrous oxide (N2O), which causes environmental problems. High nitrogencontent of cow manure causes the release of NH3, which is one of the principal malodorouscompounds produced during composting. Aerobic degradation of organic material in cow manurecauses intensive NH3 generation and emission. Ammonia volatilization leads to the loss of nitrogenand effects compost nutrition content (Pagans et al., 2006). N2O is released from nitrification or
denitrification (Fig.1) of nitrogenous compounds and has a high global warming potential (Houghton
et al., 1992). Nitrous oxide is considered 265 times more potential GHG than carbon dioxide (IPCC,
2013). Emission of these gases causes loss of nitrogen, which decreases the agronomic value ofcompost. Loss of nitrogen through ammonia volatilization can be as high as 70% (Martin and Dewaes,
1992; Eghball et al., 1997; Beck-Friss et al., 2001) and 0.62 to 1.07% in the form of N2O in manure(Hao et al., 2001). Nitrogen transformation during of manure composting is a complex mechanismⒸ ISERD

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and is shown in Fig. 1 (Wu et al., 2012). It is of great concern on developing measures for reducing
nitrogen losses during composting process to minimize the emission of hazardous gases and increase
the agronomic value of compost.
Recently, biochar amendment has been used in limiting N2O emission in manure compostingand soil (Kamman et al. 2015; Wang et al. 2013). Biochar is a carbon rich material derived frompyrolysis of biomass characterized by high number of micro pores and large surface area withnegative charge. In this study, it is speculated that these properties of biochar can reduce the emissionof NH3 and N2O when composted with animal manure as biochar can effectively retain NH3, NH4+
and NO3- in animal manure (Steiner et al., 2010).

Organic nitrogen
A
M
V
Compostingmaterial of
manureNH4+-NN

N
NO2- N

NH3

D

N20
DN

DN

N2

L
NO3--NL

Leachate

Fig. 1 Nitrogen transformation during manure composting (adopted from Wu et al., 2012)
A: Ammonification; I: Immobilization; M: Mineralization; V: Volatilization;
D: Dissolution; Nf: N-fixation; N: Nitrification; DN: Denitrification; L: Leaching loss

Therefore, this study concentrates to evaluate the effects of composting cow manure with rice husk
biochar amendment to reduce the emission of NH3 and N2O and increase the agronomic value of compost.
METHODOLOGYDesigning of Compost Box and Gas Chamber
A compost box was designed using glass container of dimension 30 cm3. The glass box was covered
with styro-foam sheets of thickness 4 cm on five sides for minimizing the heat loss (Fig. 2).

Fig. 2 Schematic diagram of composting box
and gas flux analysis

Fig. 3 Apparatus used during gas flux
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A static gas chamber was designed to measure the gas flux. A digital thermometer and a fanwere attached inside the chamber for measuring temperature and uniform circulation of air during
measurement of gas respectively (Figs. 2 and 3). The volume of air inside the chamber was calculated
as 0.017705 m3.
Conditions of the Experiment
The composting experiment was conducted from 8 August 2019 to 7 October 2019 in Laboratory ofLand and Water Use Engineering, Tokyo University of Agriculture. The average temperature was
23.0 C̊ during the experiment. Cow manure, rice straw and litter was used as main components forcomposting. The nitrogen content in cow manure and rice husk biochar was 23695 mg/kg and 1241
mg/kg respectively at the start of the experiment. Rice husk biochar was added in three different
variations (Table 1). The initial water content of the composting material was set at 70±2% for all
the treatments.
Table 1 Composition of treatments
Composition

Control

Treatment with 5%
added biochar

Treatment with 10%
added biochar

Treatment with 15%
added biochar

Cow manure (g)

3200

3200

3200

3200

Litter + rice straw (g)

1800*

1800*

1800*

1800*

250*

500*

750*

Rice husk bio-char (g)Note: * represents air-dry weight basis

Measurement of Gas Emission
Gas flux was measured using static gas chamber method with photoacoustic spectrometer. The
spectrometer used in this study was INNOVA 1412 Photoacoustic Field Gas Monitor (Fig. 3). Gas
flux was calculated using linear aggression method showed in Equation 1 (Minamikawa et al., 2015).
𝑉
𝐴

𝐹 =𝜌× ×

△𝑐
273
×
△𝑡
𝑇

(1)

where F is gas flux (mg m-2 hr-1), ρ is density of gas (kg m-3) where density of NH3 is 0.772 kg m-3
and of N2O is 1.96 kg m-3, A is bottom surface area of chamber (m2), V is volume of air inside thechamber (m3), △c/△t is average increase rate of gas density inside the chamber (10-6 m3 m-3 hr-1), T
is average temperature inside the chamber (K).
Compost Sampling and Analysis
Compost was sampled at 5, 10, 20, 30, 40 and 60 days to analyze its agronomic value. Temperatureof the compost pile was measured using Custom CT-0580 data logger and digital thermometer on
daily basis. Water content of the sample was analyzed using gravimetric method, where samples
were kept at 105°C for 24 hours. Carbon content was determined by using the formula C=0.580* IL.
Total nitrogen was analyzed by absorption spectroscopy using HC-1000 (Central Science Corp.) as
measurement device (Mihara and Ueno, 2000).
RESULTS AND DISCUSSION
Biochar Effects on Composting Temperature
Temperature of composting process is widely considered as significant factor in gas emission during
cow manure composting as microbial metabolism and activities are all temperature sensitive andⒸ ISERD

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dependent. NH3 is released when the temperature is high and are carried by thermophiles. Whereas,
N2O is released after temperature declines and mesophiles are responsible for it. In this study, all thetreatments showed a similar pattern of temperature evolution with a rapid activation of compostingprocess carried by intensive microbiological degradation of organic matter. Biochar added treatments
had increased temperature profile during the thermophilic phase compared to control (Fig. 4). The
result coincides with previous studies using biochar as a co-substrate for manure composting (Jindo
et al., 2012; Wang et al., 2013; Wei et al., 2014). It is speculated that higher temperatures in biochar
added treatments were attributed to the structure of biochar, which provided suitable habitat
conditions with positive effects on substrate properties such as porosity, surface area and moisture
content. These factors promoted microbial activity, explaining higher temperatures.
60
Control55

5%50

Temperature (

)

10%
15%

45

Ambient temp.
40
35
30
25
20
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60

Days

Fig. 4 Periodic changes in temperature with time
Biochar Effect on Ammonia Emission
Ammonia emission is inevitable during cow manure composting which has high content of nitrogen.
Generally, emission is high during early stage of composting where temperature and pH are high. In
this study, emission was high during the first week of composting which lowered gradually as thetemperature decreased for all the treatments (Fig. 5) with negligible emission after 20 days ofcomposting. The emission pattern of the results of this study coincides to that of Osada et al. (2000)
and Kuroda et al. (1996). The total ammonia emissions were significantly lower in biochar amended
treatments with 15% added treatment having the lowest emission.
0.12
5%
0.1
10%

0.08

15%

0.06
0.04
0.02
0

Cumulative gas emission (mg)0.35
Control!

Gas flux( mg mˉ² hˉ¹ )

0.14

(

denotes significance difference p<0.01)

0.3

A**

0.25
0.2

Control
5%
10%
15%

B**
C**

0.15
0.1

D**

0.05
0

1

2

3

4

5

10

15

20

0

Days

5

10

15

20

Days

Fig. 5 Periodic changes in ammonia flux

Fig. 6 Cumulative ammonia emission

The cumulative gas emission was lowered by 12.6%, 14.5% and 23.2% in 5%, 10% and 15%
biochar added treatments respectively, as compared to control (Fig. 6). The reduced emission can be
attributed to the microscopic porous structure having negative charge adsorbing ammonium ions byelectrostatic attraction (Montes-Moran et al., 2004; Nguyen et al., 2017).
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Biochar Effect on Nitrous oxide Emission
Composting of high organic content materials has been shown to produce N2O by nitrification anddenitrification under aerobic and low oxygen conditions respectively. Fig. 7 shows the periodic
change in emission between the treatments. The cumulative gas flux resulted in least emission in
15%, 10% and 5% biochar added treatments followed by control (Fig. 8). The cumulative gas
emission was lowered by 40.0%, 46.4% and 60.4% in 5%, 10% and 15% biochar added treatments
respectively, as compared to control. The result observed is supported by that of Jeffery et al., 2015,
which states that addition of biochar can decrease the emission of nitrous oxide.
Cumulative gas emission (mg)

Gas flux （ mg m-2 hr-1 ）

0.25
0.2
Control

0.15

5%
0.1

10%
15%

0.05

0.9

(

0.8

denotes significance difference p<0.01)

A, A**

Control

0.7

5%

0.6

10%

0.5

15%

A, B
A, B

0.4
0.3

B, B**

0.2
0.1
0

0
1

5

10

20

30

40

50

0

60

10

20

Days

Fig. 7 Periodic changes in nitrous oxide flux

30

Days

40

50

60

Fig. 8 Cumulative nitrous oxide emission

Biochar Effects on Agronomic Value of Compost

25000

40
(

(

denotes significance difference p<0.01)

Controldenotes significance difference p<0.01)

Control

22000

B**
B**

5%

19000

C**

10%

A**

15%

16000

35

C/N ratio

Total nitrogen (mg/kg)

Nitrogen content and C/N ratio are oftenly used as a criteria for determining the agronomic value ofcompost. Nitrogen is the most esential plant nutrient for growth and development of plants. Compost
which has high nitrogen content is considered having high agronomic value. The experimental results
showed that total nitrogen content of biochar added treatments were higher than control (Fig. 9) at
60 days of composting with 99% significant difference. The high nitrogen content in biochar added
treatments can be due to the result of reduced emission of NH3 and N2O.

5%
10%

30
A**

B**
B**

20

13000
10000

15%

25
B**

15

1

5

10

20

40

5

60

10

20

40

60

Days

Days

Fig. 9 Periodic changes in nitrogen content

Fig. 10 Periodic changes in C/N ratio

In addition, biochar may have enhanced aeration, water holding capacity and microbial activity
increasing humification of organic material. This resulted in high nitrogen content and concurrs tothat of Akdeniz (2019), El-Naggar et al. (2019) and Godlewska et al. (2017). C/N ratio is used as anindicator of compost stability and nitrogen availability. The periodic change of C/N ratio showed
better values in biochar added treatments compared to control (Fig. 10). The C/N value of biochar
added treatments at 60 days of composting had siginificant difference at 99%, compared to control.
This can be explained as increased surface area and moisture content favoured compost
microorganisms for degradation and humification of organic material. Also, biochar addition
increased sorption of nitrogen compounds in the microspores providing microorganism withⒸ ISERD

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sufficient nitrogen for their metabolism.
CONCLUSION
This study discusses the effects of composting cow manure with rice husk biochar in reducing theemission of NH3 and N2O and increasing the agronomic value of compost. A small scale laboratory
experiment was conducted where rice husk biochar were composted with cow manure The results
showed that addition of biochar is effective in reducing emission of NH3 and N2O with 15% treatment
being the most efficient. This can be attributed to the structure of biochar with high number ofmicropores and surface area that enables absorption / adsorption of NH3, N2O, water soluble NH4+
as well as NO3-. The result also showed better nitrogen content and C/N ratio in biochar-amended
treatments. The author speculates that adding of biochar helped in increasing oxygen content andretention of water enhancing better microbial metabolism and mineralization. The author believes
that composting biochar with cow manure is encouraging method for reducing emission andincreasing better quality compost. However, further researches are needed to understand the role ofbiochar and interaction of manure, biochar and microbes during composting process.
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