Livestock Research for Rural Development 31 (6) 2019 Guide for preparation of papers LRRD Newsletter

Citation of this paper

Water retention capacity of biochar and its effect on growth of maize

Nguyen Van Lanh, Nguyen Huy Bich, Bui Ngọc Hung, Nguyen Nam Quyen and T R Preston1

Faculty of Engineering and Technology, Nong Lam University Ho Chi Minh city, 70000, Viet Nam
nvlanh@hcmuaf.edu.vn
1 Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia

Abstract

It has been shown that the soil ameliorating qualities of biochar are linearly related with its effect on soil water retention capacity. It was therefore hypothesized that a simple measurement of the water retention capacity of the biochar itself could serve as an indicator of its capacity to enhance growth of plants in soils. Experiment 1 aimed to produce biochar of different qualities as indicated by its water retention capacity (WRC). The purpose of Experiment 2 was to relate the WRC of the biochar to its potential to increase the growth of maize used as indicator plant in a soil biotest.

Increasing the equivalence ratio (and thus the air flow rate) resulted in an increase in combustion temperature in the gasifier, decreased the yield of biochar but increased the water retention capacity. In a 35-day biotest, the length of maize stem and of the roots, and the weight of roots, were linearly increased by the increase in the water retention capacity of the biochar and the concentration of biochar added to the soil.

Keywords: BET test, biotest, gasification, pyrolysis


Introduction

Biochar is the byproduct of the pyrolysis of fibrous biomass at high temperatures under limited supply of oxygen. Its “quality” in terms of its capacity to enhance plant growth is usually measured by the estimation of surface area using the Brunauer–Emmett–Teller (BET) method of gas adsorption (BET_theory). The apparatus required for this test is rarely available in laboratories in developing countries, and less so at farm or household level where the biochar can be prepared in small scale gasifiers (Lanh et al 2016; Orosco et al 2018) and gasifier stoves (Gasification.pdf)

It has been shown that the soil ameliorating qualities of biochar are linearly related with its effect on soil water retention capacity (Bouaravong et al 2017). It was therefore hypothesized that a simple measurement of the water retention capacity of the biochar itself could serve as an indicator of its capacity to enhance growth of plants in soils.

There were two experiments. Experiment 1 aimed to produce biochar of different qualities as indicated by its water retention capacity (WRC), The purpose of Experiment 2 was to relate the WRC of the biochar to its potential to increase the growth of maize used as indicator plant in a soil biotest (see methodology in Rodríguez et al 2009).


Experiment 1: Producing biochar of varying qualities as determined by its water retention capacity (WRC)

Materials and methods

Biochar was made in a farm-scale gasifier constructed in our laboratory in Nong Lam University Ho Chi Minh City, Viet Nam (Photo 1; Van Lanh et al 2018)using rice hulls (varieties OM4900, IR50404 and OM5451) as biomass source. The composition of the gaseous products from the biomass gasification process was measured with the Gas board 3100P device from Wuhan Cubic Optoelectronics Co, Ltd (Photo 2). The rice hulls were gasified at increasing air enrichment ratios (ER= 0.2, 0.25, 0.3, 0.35 and 0.4). Air temperature at the time of the experiment ranged from 30 to 32o C; air humidity was 68 to 71%.(Figure 1). The water retention capacity (WRC) of the biochar was determined by suspending 100g (Wi) of dry biochar in 1 liter of water for 24h, after which it was filtered, and the wet weight of biochar determined as Wf. The water retention capacity was determined as:

WRC = [Wf-Wi)]/Wi. ……………....(1)

Statistical analysis

Linear equations were fitted to the data using the regression program in the Microsoft Excel software as in Table 1.

Table 1. Regression equations

“X” value

“Y” value

(i)

ER

Combustion temp., oC

(ii)

Combustion temp., oC

Biochar yield, %

(iii)

Combustion temperature, oC

WRC, ml/g


Results and discussion

Increasing the equivalence ratio (and thus the air flow rate) resulted in an increase in the temperature in the combustion zone of the gasifier (Table 2; Figure 1), which in turn decreased the yield of biochar (Figure 2) but increased its water retention capacity (WRC) (Figure 3). The decrease in biochar yield due to the higher temperature in the reactor, is because more of the carbon in the biochar is released in the form of gas (CO2) as can be seen in the relationship between the increase of the temperature in the reactor and the % of CO2 in the syngas (Table 2; Figure 4). This in turn leads to a decrease in the calorific value of the syngas (LHV) because CO2 is not combustible like carbon monoxide and hydrogen.

Table 2. Effect of equivalence ratio (ER) on characteristics of the syngas, the temperature in the combustion zone and
the yield and water retention capacity of biochar derived from rice husks of three different varieties

ER

CO
(%)

H2
(%)

CO2
(%)

CH4
(%)

LHV
(kcal/m3)

SGR
(kg/h/m2)

Temp.
(°C)

Biochar
yield (%)

WRC
(ml/g DM)

Rice variety OM4900

0.2

19.1

5.56

1.34

5.54

1,247

97

745

39.3

3.7

0.25

19.2

6.23

1.57

6.45

1,359

108

784

37.5

4.1

0.3

21.0

6.8

1.59

7.6

1,574

112

812

36

4.4

0.35

20.8

6.32

1.72

5.89

1,373

119

843

32.7

5.1

0.4

18.8

5.65

1.79

4.72

1,156

125

876

29.8

5.5

Rice variety OM5451

0.2

18.7

5.56

1.27

5.12

1,117

95

749

36.3

4.0

0.25

19.0

5.98

1.35

6.15

1,268

110

782

34.5

4.2

0.3

20.8

6.85

1.46

6.83

1,453

114

818

33.8

4.5

0.35

19.8

6.18

1.54

5.96

1,389

122

848

29.6

5.4

0.4

19.0

5.95

1.69

4.52

1,136

127

882

26.5

5.7

Rice variety IR50404

0.2

19.1

5.6

1.44

5.45

1,227

98

752

34.7

3.9

0.25

19.2

6.3

1.47

6.5

1,339

110

789

33.8

4.4

0.3

21.1

7.1

1.59

7.3

1,492

116

821

32.5

4.5

0.35

20.7

6.2

1.67

5.9

1,333

124

852

30.3

5.2

0.4

18.9

5.5

1.75

4.32

1,116

129

887

29.4

5.6



Figure 1. Effect of the air equivalence ratio on temperature
in the combustion zone of the gasifier		 Figure 2. Effect of temperature in the combustion zone
of the gasifier on yield of biochar


Photo 1. The downdraft gasifier Photo 2. The gasboard 3100P syngas analyzer


Figure 3. Effect of temperature in the combustion zone of the gasifier
on the water retention capacity of the biochar		 Figure 4. Effect of temperature in the combustion zone of the gasifier
on the percentage of carbon dioxide in the syngas


Experiment 2: Biotest of biochar quality using maize as indicator plant

Materials and methods

Treatments and design

The field experiment was carried out in the green house of the Research Institute for Biotechnology and Environment (RIBE), Nong Lam University from December 2018 to February 2019. Rice husk from variety IR50404 was gasified at equivalence ratios of 0.2, 0.3 and 0.4 producing biochars with WRC values of 3.9, 4.5 and 5.6 [ER is defined as the ratio of the actual air flow rate with the stoichiometric air flow rate, according to the formula ER = Qac/Qst (the stoichiometric air flow rate is the air required to burn completely the biomass)].

The three sources of biochar were then added to samples of grey soil (Table 3) in concentrations of 1, 3 and 5% (w/w basis) with 3 replications of each type of biochar at each concentration. The mixed samples (500g) of soil/biochar were put in plastic cups of 1-liter capacity. Three seeds of maize were planted in each cup, two being removed after germination to leave one single maize plant the growth of which was observed over 35 days. Urea (10g) was added once to each cup at the beginning. Water was applied equally to all cups at 0.7 liters twice daily the first week and 1 liter twice daily in subsequent weeks.

Table 3. Characteristics of the grey soil (from: Man and Hao 1993)

Soil depth

Texture (%)

pH

C%  

 N%

C/N

P2O5

K2O

0-30cm

Silt

Loam

Clay

81

5

14

5

0.53 

0.5

10

0.008

0.011

The data were analyzed with the GLM option of the ANOVA program in the Minitab (2016) software. Sources of variation were: water retention capacity of the biochar, concentration of biochar added to the soil and error. on plant growth is now a wll estabsed fact (eg:


Results and discussion

The length of the maize stem and of the roots, and the weight of roots, were linearly increased by the increase in the concentration of biochar added to the soil (Table 2; Figure 5) and by the water retention capacity of the biochar (Figure 6). Positive effects of biochar on plant growth is a well estabshed fact (eg: Rodriguéz et al 2009; Southavong and Preston 2011; Chhay et al 2013; Preston 2015). However, the positive effect on plant yield with increasing water retention capacity of the biochar has not previously beeen repeorted.

Figure 5. Growth of maize in a biotest was increased with
the level of biochar added to the soil


Table 4. Mean values for length of stem and root of maize, and weight of root, after 35 days growth,
according to WRC of the biochar and the concentration of biochar added to the soil

WRC, ml/g

Biochar in soil, %

3.9

4.5

5.6

SEM

p

1

3

5

SEM

p

Stem, cm

85.7

91

99.1

1.16

0.001

79.5

90.9

105

1.84

0.001

Root, cm

37.8

42.4

54.4

2.7

0.28

42.4

43.7

48.6

1.74

0.001

Root, g

20.4

22.6

20.7

1.74

0.62

13.7

21.6

28.4

1.74

0.001



Figure 6. Growth of maize in a biotest was increased: (i) by enriching the soil with biochar;
and (ii) by increasing the water retention capacity (WRC) of the biochar


Conclusions


References

Bouaravong B, Dung N N X and Preston T R 2017 Effect of biochar and biodigester effluent on yield of Taro ( Colocasia esculenta) foliage. Livestock Research for Rural Development. Volume 29, Article #69. http://www.lrrd.org/lrrd29/4/boun29069.html

Chhay T, Vor S, Borin K and Preston T R 2013 Effect of different levels of biochar on the yield and nutritive value of Celery cabbage (Brassica chinensis var), Chinese cabbage (Brassica pekinensis), Mustard green (Brassica juncea) and Water spinach (Ipomoea aquatica). Livestock Research for Rural Development. Volume 25, Article #8. http://www.lrrd.org/lrrd25/1/chha25008.htm

Lanh N V, Bich N H, Hung B N, Khang D N and Preston T R 2016 Effect of the air-flow on the production of syngas, tar and biochar using rice husk and sawdust as feedstock in an updraft gasifier stove. Livestock Research for Rural Development. Volume 28, Article #71. Retrieved October 2, 2017, from http://www.lrrd.org/lrrd28/5/lanh28071.html

Man N V and Hao N V 1993 Effect of plant spacing on the growth and yield of four legume trees in the grey soil of eastern south Vietnam. Livestock Research for Rural Development. Volume 5, Article #4. http://www.lrrd.org/lrrd5/1/man.htm

Minitab 2016 Minitab user's guide. Data analysis and quality tools. Release 16.1 for windows. Minitab Inc., Pennsylvania, USA.

Nguyen Huy Bich, Nguyen Van Lanh and Bui Ngọc Hung 2017 The Composition of Syngas and Biochar Produced by Gasifier from Viet Nam Rice Husk.International Journal on Advanced Science, Engineering and Information Technology, Vol 7, No 6 (2017), p. 2258-2263, DOI: http://dx.doi.org/10.18517/ijaseit.7.6.2623.

Orosco J, Patiño F J, Quintero M J and Rodríguez L 2018 Residual biomass gasification on a small scale and its thermal utilization for coffee drying. Livestock Research for Rural Development. Volume 30, Article #5. http://www.lrrd.org/lrrd30/1/jair30005.html

Preston T R 2015 The role of biochar in farming systems producing food and energy from biomass. In: Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration and Reversing CO2 Increase (Editor: Thomas J Goreau) CRC Press, Tayler and Francis Group, Boca Raton, Florida USA

Rodríguez L, Salazar P and Preston T R 2009 Effect of biochar and biodigester effluent on growth of maize in acid soils. Livestock Research for Rural Development. Volume 21, Article #110. http://www.lrrd.org/lrrd21/7/rodr21110.htm

Southavong S and Preston T R 2011 Growth of rice in acid soils amended with biochar from gasifier or TLUD stove, derived from rice husks, with or without biodigester effluent. Livestock Research for Rural Development. Volume 23, Article #32. http://www.lrrd.org/lrrd23/2/siso23032.htm

Van Lanh N, Huy Bich N, Nam Quyen N, Ngọc Hung B and Preston T R 2018 A study on designing, manufacturing and testing a household rice husk gasifier. Livestock Research for Rural Development. Volume 30, Article #35. Retrieved March 11, 2019, from http://www.lrrd.org/lrrd30/2/lanh30035.html


Received 18 March 2019; Accepted 21 May 2019; Published 4 June 2019

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