Abstract weather Bangladesh produces a huge amount of

Abstract

Biochar is getting considerable interest due to its
potential agronomic benefit through soil amendment as well as environmental
benefit through carbon sequestration. Bangladesh abounds in huge amount of
agricultural biomass which is considered significant feedstock for biochar
production. The soil of Bangladesh are facing various problems including soil
acidity problems. Soil acidity is mainly observed in the Northern and North-eastern
15 districts of the country. These areas generates 24 million tonnes of rice straw
which could be utilized as a potential source of feedstock for biochar
production. Some earlier studies reveals that application of rice straw derived
biochar into acidic soil can increase soil pH and reduce soil acidity thereby. Finally
the study concluded that application of biochar into wheat field of the acidity
affected areas of the country will reduce soil acidity and ensure food security
through increased production and crop diversity. The study insisted on more
field based research in Bangladesh context. In addition to that the study
recommended for cost benefit analysis for justifying the economic viability of
application of biochar.

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Key Words: Biochar, soil pH, residues, biomass, soil acidity.

Introduction

Biochar is a charcoal like materials produced by
thermal decomposition of organic material under limited supply of oxygen at
relatively low temperature (<7000C). Recent interest in biochar is mainly considering it's dual benefits; agronomic benefits from application into soil and it's potentials to reduce the emission of carbon dioxide through carbon sequestration. Several studies have showed it's potential to accelerate crop production through improving the physical and chemical properties of soil.The soils of Bangladesh constraints many problems including soil acidity. Excessive utilization of chemical fertilizer together with intensified crop production has lead soil acidification and nutrient deficiency. Biochar could  be considered to reclaim these degraded lands through improving the physical and chemical properties of soil.Agricultural biomass residues are considered effective feedstock for the production of biochar. Lying in the sub-tropic monsoon weather Bangladesh produces a huge amount of Agricultural biomass. These agricultural biomass are considered potential feedstock for the production of biochar which could be utilized for soil amendment to reduce the soil acidity of some acidity affected areas of Bangladesh. Different Soil Type  With Major  Soil Problems of Bangladesh   Bangladesh has a wide range of geographical conditions across the country. On the basis of physiography, soil characteristics, land levels in relation to flooding and agro-climatology, the country is divided into 30 agro-ecological zones (AEZ)(BARC,2012). Land levels in relation to flooding are classified as; high land, medium high land and low land. The nutrient status organic matter content and soil pH varies with individual AEZ.The soils of Bangladesh are facing many problems including soil acidity, low organic matter,soil salinity and nutrient deficiency . Acid sulphate soil is   one of the main problems of soils of Bangladesh covering 0.23 million hectares of land that include chittagonj, Khulna, Cox's bazar and satkhira districts. (BARC 2012)When exposed to aerobic conditions, these soils produce sulphuric acid.(Huq, et al)The soil pH of acid sulphate soil is generally below, 3.5. Acid basin clays occupy an area of 3,490 km2.These soils typically occur inhaor areas of Sylhet and Mymensingh districts,the lower Atrai basin,Trial beel,the comilla Basin and in some broad valleys  within the Madhupur and Barind Tracts.They are heavily textured soils with strongly acidic in reaction. Peat soils occupy about 0.13mha land in AEZ No.14 including Gopalgonj and Khulna districts. The soils in these areas have low bearing capacity containing more than 20% organic matter(Huq,et al).The soils are deeply flooded during rainy season, strongly acidic and have low, P, Zn and Cu availability (BARC, 2012).  Except some Gangetic alluvial soils, all soils of Bangladesh are acidic to neutral in nature ranging the pH value from 4 to 7.Excessive utilization of nitrogenous fertilizer, decomposition of organic matter in peat soil ,nitrification, Al+ toxicity result in soil acidity.(FRG,2005).Soil plateaus, raised lands and hills are usually acidic. Soil acidity adversely affects the soil fertility and crop productivity. Geo-morphologically acid sulphate soils, peat soils, acid basin clays, terrace soils and hill soils are slightly to strongly acidic in reaction. Very severe forms of acidification has been observed in the coastal areas in about 62000 ha of active acid sulphate soils (SRDI, 1963-75).Potential acid sulphate soils are reported to occupy some 8000 ha in the adjoining young tidal lands. Intensive acidification is also identified in the heavy clays in the Sylhet Basin areas, Lower Atrai Basin, and in some broad valleys within the Madhupur and Barind tracts. Northern and Eastern hills have also undergone strong acidification upto a considerable depth (BARCA1 , 1999). Nutrient unavailability together with toxicity of soil cause a huge yield loss each year. SRDI, 2012 estimates  that more than 30% crop production could be hindered due to soil acidity. Table 1:Soil acidity affected areas in Bangladesh (BARC)   Soil type pH value Areas(hectare) Very strongly acidic <4.5 2,50,270 Strongly acidic 4.5-5.5 37,07,269 Slightly acidic 5.6-6.5 27,37,997 Neutral 6.6-7.3 14,41,908 Slightly alkaline 7.4-8.4 14,35,278 Strongly alkaline 8.5-9.0 25,599 These acid soils contain lower concentration of P, toxic concentration of Al+3, Fe+3,and Mn+2 and low availability of bases which together cause reduction in crop yield. To reduce soil  acidity, it is suggested to apply lime in the soil at the rate of 1.0t/ha(Varies rate with pH value) in the areas affected with acidity having pH value below 5.5.(FRG,2012A2 ).   Fig.1: Map showing the geographical location of some areas  affected with high acidity(Red colour)(Source:BARCA3 ) The region affected with strongly to very strongly acidic soil acidity are located mainly in the northern, north-western and north-eastern hill areas of Bangladesh.The major districts include in higher acidity are :Sylhet, Sunamganj, Habiganj,  Rangpur, Nilphamari, Lalmonirhat, Panchagar, Dinajpur, Nawabganj, Naogaon,Netrokona, and Comilla.(See Fig.1) These areas are further degraded with low concentration of organic matter in soil and also nutrient deficiency (P,K,B,Zn) in the soil. Lower soil pH coupled with lower nutrient status and organic matter content of soil have lead to lower crop yield in these areas. It is expected that application of biochar will increase the soil pH of the region and give rise in nutrient availability which might result in better crop yield. 3. Effect of Biochar on soil pH: Several studies in the earlier have revealed that application of biochar into the soil can increase soil PH .A study by Zhang, et al., 2010 found increased soil pH in the soil amended with wheat straw biochar. Jones,et al., 2011 also found an increase of 0.32 unit soil pH after application of wood bioachar. Several other studies (Petter,et al., 2012, Major et al. 2010;Oguntunde,et al.,2004  )also found  an increase in pH after the application of biochar. Rodriguez,et al., 2002 observed liming effect of biochar derived from sugarcane bagasse that increased soil pH from 4.0-4.5 to 6.0-6.5.in a maize trial in Colombia. The increase of pH further varies with soil type.The pH increase in sandy and loamy soils has been reported to be larger than in clay soils(De Gryze, et al., 2010).Collins(2009)found an increase of a unit of pH by applying herbaceous biochar and 0.5-1 unit increase for applying woody biochar.Biochar is considered as potential substitute for lime. To increase soil pH, it would require 42.5 MT of biochar per hectare of land.(Collins,2009)while the rate for lime is 1.35-9.78 MT/ha (CPHA, 2002 in Galinato,et al.,2011)depending on soil. 4. Biomass availability for the production of biochar in the acidity affected areas There could be three potential sources of biomass for the production of biochar in the acidity affected 15 districts of Bangladesh. These are : agricultural residues, livestock residues and forest residues. The major crops grown in the areas are rice, wheat, jute, sugarcane, ,maize, potato ,pulse and vegetable. Table-2: Land use in the acidity affected areas:(BBSA4 ,2008,National web portal  Bangladesh) Name of the Districts   Total Cultivable land(ha) Areas under major crops(acres) Rice Wheat Jute Sugarcane Pulses Potatoc Maize Forest land(ha) Sylhet 20,o8,800 479,267 722 825 6 151 3312 Maize 24042 Sunamganj 2,76,434 409531 724 2,074 50 60 2229 360 7131 Maulvibazar 1,46,740 2,38765 430 383 155 345 4739 172 31053 Habiganj 1,54,953 610945 1417 1788 3488 964 6368 209 14954 Rangpur 2,01491 365,206 10,388 18953 3866 1560 77224 434 1595 Nilphamari 1,26,133 279,226 14465 17115 551 456 33694 34889 1063 Lalmonirhat 98,875 160300 6361 9649 102 263 9632 19515 33 Panchagarh 108200 289251 25631 24087 5236 4802 10609 49272 1866 Dinajpur 2,88,432 1419426 21678 4311 2751 500 53573 1149 7591 Nawabganj 133058 309808 40670 19959 45904 49136 2388 95984   Naogaon 2,73,832 1020065 16485 9461 3037 3225 44078 14265 2893 Netrokona 20,781 524526 2409 13255 204 862 3161 20279 738 Comilla 593380 1506554 225928 6917 1468 7857 26599 319 679 Khagrachhari 3373 85016 142 30 541 132 2159 16472 224338 Chittagonga 123097 419188 618 401 576 18321 10512 1666 170069 Total 1,282,255 8117074 368068 129208 67935 88634 290277 817 488045   The main sources of agricultural residues could be gained from rice straw, rice husk ,jute stalk, wheat straw, maize cob ,pulse, sugarcane begassae, and  vegetable residues.It is assumed that 35 %  field are  recovered without adverse effect on future yield (Foundation for alternative energy, 2005 in Hossain,2007)On the other hand  100% crop processing residues could be recovered..The field  residues recovered(35%) are mainly used for fuel purposes .The rest 65%  unrecovered biomass could be available for biochar production. It is estimated(Table 2) that 31 million tones of agricultural residues could be generated per year in the acid affected 15 districts where 20.82 million tones of  unrecovered biomass might be available for biochar production. Table 3 :Agricultural Biomass generation, recovery, available in 15 districts(metric ton) (Source :Calculated from the available data of BBS,National Web portal of Bangladesh,See Appendices 4 for calculation) Biomass Source Generation Recovery Available Rice straw 24130876.95 8445806.934 15685070 Rice husk 3812392.986 3812392.986 190619649 Jute stalk 453066.7895 158573.3763 294493.41 Wheat straw 1060947.277 371331.5471 689615.73 Maize 1298687.077 454540.4769 844146.6 Pulse 122213.8846 42774.85962 79439.025 Sugarcane bagasse 351167.1593 351167.1593 175583.58 Vegetable 577776.8 202221.88 375554.92 Total 31807128.93 13838809.22 208763553 Besides, each of the 15 districts has some forest lands which are a good source of biomass. Forest biomass includes trunks, branches, leaves, bark, roots, twigs, and saw dust both from homestead trees and reserve forest. Data regarding how much forest residues are generated in the 15 districts are not available. However, the total generation of forest residues in the country is 17.442 million tons(Halder,et al.,2o14).As the  15 districts comprise 7.65% of the total forest land of the country(BBS). It is calculated that the total generation of forest residues could be 1.3 million tons in the region.   Another potential source for biomass in these areas could be waste from livestock . The total dry biomass residue recovery (Cow dung, poultry litter)is estimated  8.98 million tons per year(calculated from available data of BBS, and Nationnal web portal,see calculation in appendices 1) . From the above discussion it is clear that among the three potential sources of biomass,  agricultural residues  contribute the highest amount of biomass generating 31.80 million metric tons of biomass of which 20.87 million metric tons are currently unused being available for biochar production in these areas.   Fig.2: Composition of Agricultural biomass in the 15 districts   Rice straw further, constitute the highest  percentage(76%) among all other agricultural  biomass  which could be the prime source of biomass in the acid affected districts.   5.Properties of Rice Straw Derived(RSD) Biochar  Physical and chemical properties of Biochar largely depends on the type of feedstock, pyrolysis temperature and also duration of heating. The normal cation exchange capacity in soil is <3 cmol/kg for sandy soil and >25 cmol for soils with high clay or
organic matter(40,Wu,et al.,2012) whereas the
CEC in RSD biochar was found 46-61 cmol/kg which can enhance the adsorption
ability to retain cationic nutrient.The rice straw-derived biochars especially
produced at 400°C had high
alkalinity and cation exchange capacity, and high levels of available
phosphorus and extractable cations(Wu, et al., 2012) The higher pH and
alkalinity of RSD biochar can potentially increase  soil pH and neutralize soil acidity  thereby . In addition to that RSD bichar can
reduce the availability of exchangeable Al in the soil to alleviate the
possible toxic effects(Van Zwieten,et al.,2010) A  study (Jiang, T et. al., 2012) revealed  an increase of pH from 4.9 to 6.13 by
amending acidic soil (oxisol) with 5% RSD biochar. Overall biochar produced
from rice straw at temperature of 400°C
shows the greatest potential to improve the fertility of highly weathered and
infertile soil(Wu et al.,2012)

Table:4 A comparison between RSD biochar and biochar derived from
other feedstock.

 

Feedstock of Biochar
 

pH

Total C

Total N

C:N

Ca

Mg

K

CEC

Ref.

(%)

 

RSD biochar (400 oC)

9.96-10.62

50a
 

1.68a

 

12.2-13.4

4.1-3.9

61.3-61.4

46.1-61.6

Wu, et al.,(2012)

 

 

59.9b

 

 

24.6-29.9

 

Peng, et al., (2011)

 

 

 

 

 

 

 

 

Paper mill waste-1
(Waste wood chip)

9.4

50.0

0.48

104

6.2

1.20

0.22

9.00

Zwieten, et
al., (2010

Paper mill waste-1
(Waste wood chip)

8.2

52.0

0.31

168

11.0

2.60

1.00

18.00

Zwieten, et
al., (2010)

Green
waste
 

9.4

36.0

0.18

200

0.4

0.56

21.00

24.00

Chan, et al., (2007

Eucalyptus biochar

82.4

0.57

145

4.69

Noguera, et
al., (2010)

Cooking biochar

72.9

0.76

96

11.19

Noguera, et
al., (2010)

Poultry litter (450oC

9.9

38.0

2.00

19

Chan, et al., (2008)

Poultry litter (550oC)

13

33.0

0.85

39

Chan, et al., (2008)

Wood biochar

9.2

72.9

0.76

120

0.83

0.20

1.19

11.90

Major et al., (2010)

Hardwood sawdust

66.5

0.3

221

Spokas, et
al., (2010)

a  = Lu, et al.2014) b= 400°Ct.and 8 h duration

The above table shows
that the  pH value and CEC is higher
in  RSD biochar  as compared to other organic bioch. Peng et.al,2011 opined that RSD biochar play much more
important role than fertilizer as soil conditioner by increasing soil pH and
CEC.The study found an increase in soil pH by o.1-O.46 unit and CEC by
3.9-17.3% by adding 1% biochar(equivalent to 2.4ton/ha) in highly weathered
ultisol (pH 4.1).The above discussion reflects the potential for  rice straw to be used as biochar feed stock
to reduce soil acidity.

6.Suitable
crops for application of Biochar

Three different
scenario for three different crops have been considered to justify the
availability of biomass  for the
production of biochar .Assuming 100% of generation  would be utilized for biochar and the yield
rate for biochar 30%, 9.54 million tons of biochar could be made from the  rice straw generated in the areas .This
amount of biochar are not sufficient  for
application into rice field requiring 65 million tons of biochar at a rate of
20t biochar/ha. On the other hand production of biochar would be sufficient to
apply in to in wheat field considering the utilization of biochar in all
possible scenario(Table -5)

Table 5:Yield
possibility  of RSD biochar with the
available feedstock in acid affected 15 districts

Utilization of rice straw

Wheat field
(149015.4 ha)

Maize
(103563.6 ha

Rice areas
(27504.05 ha)

 

Biochar 
production
(million tons)

Required

Biochar 
production
(million tons)

Required

Biochar 
production
(million tons)

Required

100% of generation

9.54

 
2.98
Million tons

9.6

 
2.07
Million tons

9.54

 
65
Million tons

Recovered biomass only

4.14

3.37

4.14

Unrecovered biomass  only

6.2

6.2

6.2

Rice is grown in
slightly acidic soil(5.5-6) while wheat grows well in soil with higher
pH(6-7).Wheat is the second major cereal crop of Bangladesh that grows in soil
with higher pH (6-7) soil..The results of some previous studies(Van Zwieten et
al.,2007,Solaiman et al.,2010, Blackwel et al.,2010)
show that incorporation of biochar into wheat field comparatively at a lower
rate(1-6 ton/ha) can increase the yield rate of wheat upto 46%. Although the
average yield rate of wheat in Bangladesh is 2.78 t/ha, the yield rate of wheat
in acidic soil of northern and north- eastern part of Bangladesh is
considerably lower(DAE).One of the reasons behind lower yield could be soil
acidity.Considering the above issues this study consider wheat field for
application of biochar. The pH level in these areas is also significantly lower
(4.5 to 5) compared other parts of the country. BARI suggest to apply
agriculture lime at a rate of 1 ton/ha in acidic soil to raise the pH. But the
lime has GHGs potential at a rate of 0.22MT of CO2 per ton of
lime.To avoid the emission, biochar could be considered as a potential
substitute for agricultural lime in the region with acidic soils.

7.Conclusion

Bangladesh
produces substantial amount of biomass which shows potentials for biochar
productio in Bangladesh.. Considering the huge availability, rice straw seems
to be the prime candidate to be used as feedstock for biochar. The physical and
chemical properties of RSD biochar also gives confidence to be used for soil amendments.
The Northern and North-Eastern 15 districts with higher level of acidity seem
to be highly benefited from application of biochar. The application of biochar
will increase soil pH of the acidity affected areas of the country and reduce
soil acidity thereby. In this way more agricultural land will be taken under
cultivation which in turns bring food security for the people through increased
yield and crop diversification. Due to yield uncertainty and shortage of
required amount of biomass, rice may not be a suitable crop for utilization of
biochar. As wheat is the second major crop showing positive agronomic benefit
after amendment with biochar, this study suggests incorporation of biochar for
soil amendment in wheat field of Bangladesh. Some other crops like Maize,
Mungbean, and Tomato which grow at higher pH also might get similar benefit
while amendment soil with biochar. The agronomic benefits from utilization of
RSD biochar which have been described in the study are based on the result of
previous studies. To ensure the degree of certainty, more field based research
in Bnamgladesh context is required. Further the study requires cost benefit
analysis to justify whether the application of biochar would be economically
viable.

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