Biochar from water hyacinth

Catena 111 (2013) 64–71

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Biochar from water hyacinth (Eichornia crassipes) and its impact on soil biological activity R. Ebhin Masto ⁎, Sandeep Kumar 1, T.K. Rout 1, Pinaki Sarkar 1, Joshy George 1, L.C. Ram 1 Environmental Management Division, CSIR–Central Institute of Mining and Fuel Research, Digwadih Campus, Dhanbad 828108, India

a r t i c l e

i n f o

Article history: Received 25 October 2012 Received in revised form 8 June 2013 Accepted 28 June 2013 Keywords: Biochar Eichornia Microbial biomass Soil enzyme Respiration

a b s t r a c t Biochar is a useful material for carbon storage in soils. In this report, we explored conversion of water hyacinth (Eichornia crassipes) to biochar as a sustainable weed management strategy, as it also has potential for improving soil quality. Eichornia biomass samples were carbonised with limited supply of air in a muffle furnace at varied temperature (200 to 500 °C) and residence time (30 to 120 min). The biochar yield decreased with temperature and time, but biochar carbon stability increased with temperature. The optimum condition for obtaining maximum stable carbon in Eichornia biochar (EBC) is 300–350 °C temperature with 30–40 min residence time. TGA and FTIR studies showed that EBC has increased aromaticity and carbon stability compared to the starting biomass. Impact of the EBC on soil quality was studied using a red soil, from Dhanbad, India. Soil biochemical properties (dehydrogenase, fluorescein hydrolases, catalase, respiration, active microbial biomass) and maize seedling growth were used to investigate the effects of biochar addition to the soil. Maize seedling vigour index increased from 1.0 at control to 1.61 in 20 g/kg EBC treatment. The maximum increase in soil enzymes like acid phosphatase activity (+32%), alkaline phosphatase activity (+22.8%), and fluorescein hydrolases activity (50%) occurred at the EBC dose of 20 g/kg. EBC significantly enhanced the soil biological activity particularly the active microbial biomass which has increased by 3 times and soil respiration by 1.9 times. The study shows that the waste Eichornia weed could be gainfully utilised as a soil quality amendment material by converting it to EBC. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Eichornia crassipes (water hyacinth) is one of the world's most recalcitrant weeds, originated from Amazon basin, in the lakes and marshes of the Pantanal region of western Brazil (Barrett, 1989). It was introduced into India as an ornamental plant in 1896 from Brazil (Rao, 1988); now it has a near worldwide distribution. Eichornia is a stubborn weed and its management can assume serious environmental issue due to its high reproductive (vegetative and sexual) rate and dispersion (Téllez et al., 2008). It can constitute ecological menace for bodies of water, lakes, irrigation structures, etc. The presence of Eichornia on water surfaces increases the evapo-transpiration rate and it acts as channels for greenhouse gas emissions from water bodies. The main management strategy of Eichornia is via physical removal from water bodies and disposal.

⁎ Corresponding author at: Environmental Management Division, CSIR–Central Institute of Mining and Fuel Research, Digwadih Campus, PO: FRI, Dhanbad 828108, Jharkhand, India. Tel.: +91 326 2388339; fax: +91 326 2381113. E-mail address: [email protected] (R.E. Masto). 1 Tel.: +91 326 2388339; fax: +91 326 2381113. 0341-8162/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.catena.2013.06.025

Eichornia has high biomass yield (100–120 t/ha/yr), and it contains valuable plant nutrients and thus it is a potential resource for soil reclamation. Eichornia biomass is essentially cellulosic and if incorporated in soil in this form, the biomass carbon will decompose readily and release to atmosphere. Conversion of the biomass to biochar (BC) would enhance the stability of the carbon and supports long-term carbon storage in soil (Jeffery et al., 2011). Pyrolysis and gasification are used to convert bulky and heterogeneous biomass into useful forms tailored to user needs (Kim et al., 2012). During pyrolysis, cellulosic carbons in biomass can be converted to more stable aromatic carbons as BC. This stable carbon and its tendency towards slow decomposition in soil are attracting interest for application of BC for boosting soil carbon. BC is being recognised as an interesting material to mitigate global climate change (Lehmann, 2007). It has been reported that the turn over time of BC in soil ranges from less than 100 years to more than million years (Nguyen et al., 2008), thus, BC can constitute a significant carbon sink in the global carbon cycle (Harvey et al., 2012). Conversion of Eichornia to BC represents a more sustainable strategy for management of this weed. BC from Eichornia biomass will enhance carbon storage and fertility of soil, hence, the hitherto recalcitrant weed, Eichornia, then becomes a valuable resource. Thus, the present study was aimed at BC production from the Eichornia biomass; evaluation of the potential of Eichornia biochar (EBC) for improving soil quality (soil enzymes, microbial biomass, respiration, etc.); and the effect of EBC on the germination and growth of the test crop, Zea mays.

R.E. Masto et al. / Catena 111 (2013) 64–71

as and when needed, and the maize plant was harvested after 20 days. Data on percent seed germination, shoot length, root length, shoot weight and root weight were recorded. Seedling vigour index (SVI) was calculated as below:

2. Materials and methods 2.1. Biochar preparation from Eichornia Eichornia biomass collected from Manjhi Basti, Dhanbad, India was air dried and cut to small pieces (30–50 mm). The biochar was prepared under limited supply of air in 500 ml cylindrical stainless steel box (11 × 7 cm, height × diameter) with perforated lid containing nine holes, each of 4 mm diameter. We prepared EBC in a perforated box with limited supply of air as our objective was to simulate a simple pyrolysis condition that could be easily adopted by farmers with minimum investment. Known quantity of air dried material was taken in stainless steel box, closed with perforated lid, and heated in muffle furnace at different temperature (200, 250, 300, 400, 500 °C), and time (30, 60, 90, 120 min). After carbonization, the biochar yield was recorded. The resultant EBC was characterised for oxidisable organic carbon (OC) content by potassium dichromate oxidation method (Walkley and Black, 1934). This wet oxidation with potassium dichromate was used to estimate the labile fraction of C in biochar (Calvelo Pereira et al., 2011). Loss on ignition (LOI) was determined by heating the EBC (taken in an open silica crucible) in a muffle furnace at 750 °C for 6 h (ASTM method, D-1762-84). Carbon lability index was calculated as the OC/LOI ratio (Blair et al., 1995). Stable organic matter (SOM) was calculated as below: SOM ¼ LOI−ðOC 1:724Þ

ð1Þ

where, 1.724 is the factor to convert organic carbon to organic matter. Stable organic matter yield index (SOMYI) was determined as per the following equation: SOMYI ¼ ðChar yield=100Þ SOM:

65

ð2Þ

The process parameter for biochar preparation was optimised to get maximum SOMYI using response surface method. The elemental composition and the morphological properties of the EBC were determined by elemental analyzer (Elementar, Vario EL III) and scanning electron microscopy (JEOL, JSM-6390LV) respectively, at the Sophisticated Test and Instrumentation Centre, Cochin University of Science and Technology, India. The spectral properties were determined by infrared spectrophotometer (Bruker). Differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA) have been carried out in a simultaneous thermal analyzer (Netsch, 409C), where the sample was heated with a flow of air (50 ml/min) at a heating rate of 10 °C/min. 2.2. Pot experiment EBC prepared at 300 °C with 30 min residence time was used for the pot experiment. Red soil collected from Digwadih, Dhanbad, India was used for the evaluation of the beneficial effect of EBC on soil. The area experiences tropical climate and is characterised by very hot premonsoon and cold winters. The month of May and half June is the peak of pre-monsoon season with an average maximum temperature of 44 °C, while December and January are the coldest months. Bulk soil sample (0–15 cm depth) was collected from an uncultivated fallow land (approximate geo-reference: 23°41′18.39″N and 86°24′29.63″E). The soil is Ustorthents, as per the USDA soil classification system, originated from Gondwana formations. The soil was air dried, passed through 2 mm sieve and treated with EBC at different doses (0, 1, 3, 5, 10 and 20 g/kg). The experiment was carried out in plastic containers of 0.5 kg capacity; there were 6 treatments and 3 replications. Three healthy maize seeds were sown on each pot. The pots were irrigated

SVI ¼ ½GT ðSLT þ RLT Þ=½GC ðSLC þ RLC Þ

ð3Þ

where, GT and GC are germination percentage under treated and control soils respectively; SL and RL are respective shoot length and root length. 2.3. Soil analyses After the harvest of maize, soil samples were collected from all the pots and analysed for different parameters. Soil pH and electrical conductivity (EC) were determined in 1:2.5 soil–water suspensions using a glass electrode and conductivity bridge, respectively (Tandon, 1995). Active microbial biomass carbon (AMBC) was measured by the glucose nutrient induced respiration method (Islam and Weil, 2000). Soil dehydrogenase activity (DHA) was determined using the method of Klein et al. (1971). Catalase activity (CAT) was determined as the amount of H2O2 consumed by the soil as described by Xu and Zheng (1986). Fluorescein diacetate hydrolase activity (FDA) of the soil was determined by the method described by Dick et al. (1996). Phosphatase activity of the soil was determined by the method of Tabatabai and Bremner (1969). Basal soil respiration (BSR) was measured as the CO2 evolved from moist soil, adjusted to 60% water holding capacity (WHC), over an incubation period of 10 days at 25 ± 1 °C, in the dark (Islam and Weil, 2000). Metabolic quotient (qCO2) was calculated as BSR per unit of AMBC (Anderson and Domsch, 1990; Islam and Weil, 2000). 2.4. Statistical analysis Response surface method was employed for optimization of temperature and residence time for preparation of biochar. One-way analysis of variance was carried out to compare the means of different treatments, and least significant differences at P b 0.05 were obtained using Duncan's multiple range test (DMRT). Statistical software SYSTAT-12 was used for response surface method (RSM) and other statistical analysis. 3. Results and discussion 3.1. Biochar preparation The EBC yield decreased with increasing pyrolysis temperature and residence time (Fig. 1). EBC yield decreases more sharply at temperature above 400 °C. High pyrolysis temperature increases the rate of dehydration and release of volatile components of the biomass, and tendency of biomass loss through combustion increases with duration of the pyrolysis (Mašek et al., 2011). Stable carbon in the BCs appears to increases with increasing pyrolysis temperature as shown by the trend of oxidisable carbon (OC) of the EBC. Similar trends had been observed by Calvelo Pereira et al. (2011), Baldock and Smernik (2002), and Bruun et al. (2008). LOI decreased with increase in temperature and time. This reflects increase in ash content in the EBC at high pyrolysis temperatures. Highest ash content (69%) was observed at 500 °C. Bird et al. (2011) reported 73.4% ash content for algal biochars, but they commented on the possibility of secondary carbonate formation at high ashing temperatures, leading to an over estimate. The carbon lability index (OC/LOI) of the EBC decreased with increasing temperature and duration of pyrolysis. Stable organic matter (SOM) content of the EBC increased with increase in temperature and time. But the SOM shows a peak at 300 °C after which it decreased probably due to the increase in ash content (Fig. 1). When applied in agricultural soils, the biochar will be exposed to numerous physical, chemical and

66


Char yield

200

250

300

Temperature

30 min

60 min

90 min

120 min

400

Oxidisable organic carbon (%)

60 min

90 min

120 min

40 20 0 200

0.60

30 min

60 min

40

90 min

120 min

30 20 10 300

300

500

400

Carbon lability index 30 min

60 min

90 min

120 min

0.30 0.20 0.10 0.00

500

200

250

300

400

500

Temperature (°C) Stable organic matter yield index

30 min

60 min

90 min

120 min

400

500

Temperature (°C)

Stable organic matter yield index

Stable organic matter

250

400

0.40

Stable organic matter

200

300

0.50

Temperature (°C)

50.00 45.00 40.00 35.00 30.00 25.00 20.00 15.00 10.00 5.00 0.00

250

Temperature (°C)

50

250

30 min

80 60

500

60

200

100

(°C)

Oxidisable organic carbon

0

Loss on ignition (%)

Loss on ignition 120

Carbon liability index

Char yield (%)

70 60 50 40 30 20 10 0

14.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 200

250

300

30 min

60 min

90 min

120 min

400

500

Temperature (°C)

Fig. 1. Impact of pyrolysis temperature and residential time on char yield, and other char parameters.

biological processes (Mašek et al., 2011), thus, the stability of applied biochar is very critical. The maximum SOM was observed at 300 °C and 90 min duration, but the corresponding EBC yield was only 13%. However, for carbon storage in soil, the yield of the stable carbon is more important than its mere concentration in biochar (Mašek et al., 2011). Thus we proposed the stable organic matter yield index (SOMYI), Eq. 2. The calculated SOMYI decreased at temperature N300 °C (Fig. 1). Also at 300 °C, SOMYI decreased with increasing pyrolysis time. This shows that optimum SOM yield tends towards moderate pyrolysis conditions. The response of SOMYI to pyrolysis time and temperature is presented in Fig. 2. The SOMYI increased up to 300–350 °C, thereafter it decreased. Based on desirability analysis, the optimum condition was found to be heating Eichornia at 300 °C for 40 min. As the goal of biochar is for soil amendment to improve soil fertility, SOM yield is important, rather than the SOM content. Thus, we recommend a low temperature moderate pyrolysis (300–350 °C, 30–40 min) condition for preparation of EBC from Eichornia biomass. 3.2. Characterisation of the Eichornia biochar C, N, and S contents were increased in EBC as compared to the starting biomass, whereas, O and H content decreased (data not given). The C enrichment factor (Cbiochar/Cbiomass) for EBC is 1.20. We employed H/C and O/C ratios as an indication of degree of aromaticity of biochar carbon (Killops and Killops, 2005). The H/C and O/C atomic ratios of the Eichornia biomass are 1.71 and 0.78 and the respective values for EBC are 0.85 and 0.33. The decrease of these ratios suggests higher degree of aromaticity in EBC. The infrared spectra of the EBC, prepared at 300 °C and 500 °C are shown in Fig. 3. The absorption bands (Coates, 2000) of the FTIR spectra are assigned as follows: 1616 and

1427 ― of C_C\C aromatic ring stretching; 1321 ― aromatic C\H stretch; 1032 ― C\O\C stretch associated with \OH bend cellulose, hemicelluloses and lignin; 877 and 782 ― aromatic C\H out-of-plane bends. The spectra of EBC—500 °C show higher intensities of aromatic absorption bands than those of EBC—300 °C, indicating an increase of aromatic C for the EBC prepared at 500 °C than that of 300 °C. The scanning electron microscope (SEM) images (Fig. 4) for EBC showed puffy surfaces. When the Eichornia biomass is heated, volatile matters release out of the biomass which creates micropores on the surface, while the volatiles trapped inside the biomass expand the microstructure. Thus the resulting EBC is with high surface area and porosity. These two properties are particularly useful for soil application of biochar especially for enhancing soil water holding capacity, nutrient retention, harbouring micro-organisms and increasing the fertiliser use efficiency, etc. The SEM–EDX (Fig. 4), shows the composition of the biochar particles. The main elemental compositions of the particles in decreasing order are C N O N K N Cl N P N Mg N Si. Thermo gravimetric analysis (TGA) is a useful tool for obtaining information about thermal degradation of materials. Application of TGA for studying thermal stability of biochar has the advantage of avoiding extraction steps (Enders et al., 2012; Gascó et al., 2012). TGA of the Eichornia biomass and the respective EBCs prepared at 300 and 500 °C were carried out to gain insights on their thermal stability. Fig. 5 shows TG curves and the weight loss (DTG) of the biochar. From the TG/DTG curves, the weight loss at temperature b 250 °C can be attributed to loss of adsorbed water and partial dehydration of the cellulose structural units. The weight loss at 250–300 °C may be assigned to the degradation of hemicellulose and cellulose, while the weight loss at N400 °C may be due to decomposition/degradation of the remaining cellulose and lignin (Girisuta et al., 2008; Zhou et al., 2009). Comparison


67

Fig. 2. Response surface plot of SOMYI (stable organic matter yield index) of Eichornia biochar.

of the TGA–DTG and DSC curves of biomass and biochar shows characteristic shifting of DTG plot towards higher temperature range especially for EBC—500 °C. This shift in DTG depicts stability of the organic carbon in the EBC than the biomass. The weight of residual material at 600 °C (in TGA) was higher for EBC than for biomass materials. This may be due to higher ash content of the biochar than the biomass. In EBC 500 °C, the peak for lignin reaction has shifted to low temperature probably due to the catalytic role of potassium that it strongly promotes the decomposition reaction of cellulose (Nowakowski and Jones, 2005). The reported K2O content in Eichornia ash ranged from 6.3–34.1% (Gopal, 1987). The influence of potassium in char formation has also been reported by Zhou et al. (2009). High potassium content promotes

0.03

dissolution/degradation of cellulose and lignin and affects the thermal stability. In the present study, the catalytic shift in DSC peak is attributable to the influence of the high K concentration (5.1%, Fig. 4) in the EBC. Adopting thermal degradation mechanism described by Galvez et al. (2012) three weight loss steps were identified. WL1 was assigned to water release from the samples which continues to take place up to temperature around 180 °C. After 180 °C the net weight loss is basically due to release of volatile organic components. WL2 and WL3 were assigned to combustion of labile and stable organic components, respectively. The TG and DTG revealed that the WL2 occurred at temperature range 180–450 °C for the starting biomass and EBC—300 °C, whereas, for EBC—500 °C, WL2 occurred at 180–420 °C. Accordingly,

EBC 300 EBC 500 1032

0.025

782

1616

1321

877

1427

0.015

0.01

0.005

500°C

300°C

0 3997 3911 3824 3738 3651 3565 3479 3392 3306 3219 3133 3046 2960 2873 2787 2700 2614 2527 2441 2354 2268 2182 2095 2009 1922 1836 1749 1663 1576 1490 1403 1317 1230 1144 1057 971 885 798 712

Absorbance

0.02

Wave number (cm-1) Fig. 3. FTIR spectra of Eichornia biochar.

68


Fig. 4. SEM-EDX of Eichornia biochar.

the respective WL3 for the starting biomass and EBC—300 °C is between 450–600 °C; however, WL3 for EBC—500 °C ranged from 420–600 °C. This may be due to the aforementioned influence of potassium content in the samples. Thermo stability index (WL3/WL2) and weight loss associated with loss of organic matter combustion (Worg = WL2 + WL3) are presented in Table 1. Thermo stability index value of EBC—300 °C is higher than that of EBC—500 °C, which implies that loss of organic matter (WL3) is lower for EBC—300 °C compared to EBC—500 °C. Therefore preparation of EBC at 300 °C is more beneficial for soil amendment purpose as compared to the higher temperature EBC. 3.3. Impact of Eichornia biochar on maize seedling growth and soil biological activity The germination percentage of Z. mays increased from 78% in control to 100% at 20 g/kg EBC (Table 2). The shoot length (increased from 22 to 33 cm), root length (15.7 to 20.2 cm), shoot weight (1.13 to 1.69 g/pot), and root weight (0.34 to 0.57 g/pot) significantly increased with EBC application at 20 g/kg. The improved crop growth in biochar incorporated soil is normally due to liming effect, improved water holding capacity and nutrient availability of the soil (Jeffery et al., 2011). The soil used in the present study has neutral pH (Table 3) and the crop trial was carried out in a pot culture with uniform irrigation. Hence, the enhanced growth of the maize may be mainly attributed to the nutrient contents in EBC. Gopal (1987) reported the rich content of plant nutrients in Eichornia ash (28.7% K2O, 1.8% Na2O, 12.8% CaO, and 7.0% P2O5). In a pot trial, Peng et al. (2011) reported that maize biomass yield increased by 64% (without NPK) to 146% (with NPK) after biochar

amendment. In our study the seedling vigour index increased from 1.0 at control to 1.62 at 20 g/kg EBC treatment. Along with its nutrient content, EBC may also contribute to increase in cation exchange capacity, which can increase seed germination, plant growth and crop yield (Glaser et al., 2002). The electrical conductivity and the soil pH increased significantly with EBC addition (Table 3). This is in agreement with related studies where biochar application increased the pH in acidic soils (Chan et al., 2007; Lehmann et al., 2003; Uzoma et al., 2011). Compared to the control, addition of the EBC increased soil pH by 0.01–0.19 unit (P b 0.05) and electrical conductivity by 1.4 to 4.8 times. Presence of alkaline metal (Ca2+, Mg2+, and K+) oxides in BC was assumed to explain such increase in pH (Steiner et al., 2007). Addition of biochar significantly increased EC; however, the increase in EC did not affect the maize seedling growth, rather the seedling vigour increased significantly even at the highest EBC dose of 20 g/kg soil (Table 2). Soil dehydrogenase (DHA) and catalase (CAT) activities increased significantly with increasing dose of EBC application (Table 3). It has been shown that soil DHA activity increased with application of chicken manure biochar (Park et al., 2011); sewage sludge biochar (Paz-Ferreiro et al., 2012). Further, Paz-Ferreiro et al. (2012) observed higher DHA coupled with lower respiration values in biochar amended soils which indicated the improvement in the efficiency of soil microorganisms under biochar treatment. DHA increased by 1, 6, 7, 14 and 21% for 1, 3, 5, 10, and 20 g/kg EBC additions, respectively. The increase in AMBC (Table 3) might have contributed to the increase in DHA as this is a group of intracellular enzymes present in active microorganisms in the soil (Nannipieri et al., 1990). DHA is considered an integrative soil


69

Fig. 5. TGA–DTG and DSC curves of Eichornia biochar and the biomass (EBC — Eichornia biochar).

biological indicator, its improvement after EBC amendment reflects the overall beneficial effect of EBC. CAT increased significantly with EBC application and reached a maximum at 20 g/kg EBC. The results clearly indicate that EBC can greatly increase the oxidative capacity of soil microorganisms. No adverse effect was noticed for DHA and CAT even

at the highest dose of 20 g/kg biochar which indicates the beneficial effect on EBC on soil microbial activity. The hydrolytic enzymes like FDA, acid and alkaline phosphatase were also increased in biochar added soils (Table 3). Although soil amendment with organics (pig slurry digestate, rapeseed meal, wheat

70


Table 1 Thermal analysis of Eichornia biomass and biochar (EBC, Eichornia biochar).

WL1 (mass loss %) WL2 (mass loss %) WL3 (mass loss %) Thermo stability index (WL3/WL2) Weight of organics (%)

RT–180 180–450 180–420 450–600 420–600

°C °C °C °C °C

Eichornia biomass

EBC—300 °C

10.4 51.0

6.43 36.3

12.4

21.3

EBC—500 °C 7.8

application have been reported by Liang et al. (2010), Jin (2010), and Paz-Ferreiro et al. (2012). BSR/AMBC has been used as stress indicator, at higher rates of EBC which probably the soil microorganisms have to expend more energy for growth and maintenance. The decrease in metabolic quotient in our study supports the beneficial role of EBC.

16.1

1.19 63.4

3.31 57.6

17.85 2.29 33.9

starch) can significantly increase the activity of hydrolytic enzymes (β-glucosidase, leucine amino peptidase and alkaline phosphatise), however, green waste biochar did not increase the hydrolytic enzymes activities (Galvez et al., 2012). Paz-Ferreiro et al. (2012) and Lammirato et al. (2011) found that β-glucosidase activity diminished in the biocharamended soils. The maximum increase in acid phosphatase activity (32%); alkaline phosphatase activity (22.8%), and FDA activity (50%) occurred at the highest EBC dose of 20 g/kg. Paz-Ferreiro et al. (2012), observed an increased phosphomonoesterase activity due to biochar, while aryl sulphatase activity exhibited no difference between biochar treatments. AMBC increased from 48 mg/kg in control to 153 mg/kg at 20 g/kg EBC treatment (Table 3). Evidence of microbial activity increase in char treated soils is reviewed (Atkinson et al., 2010; Lehmann et al., 2011) and is mostly due to improvement of physical and chemical characteristics of the soil. BSR values ranged from 427 mg CO2/kg/10 days in control to 819 in 20 g/kg EBC treatment. The increase in BSR is probably due to the addition of some labile C from biochar. Kolb et al. (2009) reported increase in soil respiration after biochar (from dairy and bull manure) additions. The metabolic quotient calculated as the BSR/ AMBC ratio decreased with increasing rate of biochar, and was lowest (5.35) at 20 g/kg EBC. The lower metabolic quotients due to biochar

4. Conclusions Conversion of Eichornia biomass to biochar and application of the biochar to soil can turn the hitherto waste weed into useful material for soil carbon sequestration and for improving soil fertility. The biomass-to-biochar conversion process optimisation study indicated that stability of biochar carbon increased but biochar yield decreased with increase of pyrolysis temperature. The yield of stable organic matter fraction was found to be optimum at 300–350 °C temperature and 30–40 min residence time. Elemental analysis, TGA, and FTIR, revealed the aromaticity and stability of biochar carbon. Laboratory experiment on agronomic benefit of the EBC with Z. mays showed that the seedling vigour index increased significantly up to 20 g/kg biochar. Addition of biochar to red soil (up to 20 g/kg) has significantly enhanced the soil biological activity assessed through different enzymes, microbial biomass, respiration and metabolic quotient. Active microbial biomass carbon increased by 3.0 times, and soil respiration by 1.9 times due to biochar application. The results of this study support that the conversion of Eichornia to biochar could be a sustainable option for gainful use of this weed.

Acknowledgement We express our thanks to Director, CSIR–Central Institute of Mining and Fuel Research, Dhanbad, India for supporting this publication. We acknowledge financial support of Department of Science and Technology, India under “Fast Track Scheme for Young Scientist (SR/ FTP/ES-28/2007)”. The support of Mr. James for his comments on this manuscript and English editing is acknowledged.

Table 2 Effect of Eichornia biochar on maize seed germination and seedling growth (within each row, values with the same letter are not significantly different at P b 0.05 level following DMR test).

Germination (%) Shoot height (cm) Root length (cm) Shoot weight (g/pot) Root weight (g/pot) Seedling vigour index

Control

Soil + EBC (1 g/kg)

Soil + EBC (3 g/kg)

Soil + EBC (5 g/kg)

Soil + EBC (10 g/kg)


78a 22a 15.7a 1.13a 0.34a 1.0a

80a 24a 16.3a 1.28b 0.36a 1.04a

84b 27ab 16.6b 1.33b 0.41a 1.17b

94c 28ab 16.8b 1.48c 0.48b 1.36c

94c 30ab 17.4bc 1.57cd 0.55bc 1.44c

100d 33b 20.2c 1.69d 0.57bc 1.62d

Table 3 Effect of Eichornia biochar on soil quality parameters (within each row, values with the same letter are not significantly different at P b 0.05 level following DMR test).

pH Electrical conductivity(dS/m) Catalase activity (vol. of 0.1 N KMnO4/g soil) Dehydrogenase activity (mg TPF/kg/24 h) Alkaline phosphatise activity (μg PNP/g/h) Acid phosphatase activity (μg PNP/g/h) Fluorescein diacetate hydrolase activity (mg fluorescein/kg/h) Active microbial biomass carbon (mg/kg) Basal soil respiration (mg CO2/kg/10 days) Metabolic quotient (BSR/AMBC)

Control

Soil + EBC (1 g/kg)

Soil + EBC (3 g/kg)

Soil + EBC (5 g/kg)



7.29a 0.159a 0.15a 833a 35a 25a 1.94a 48a 427a 8.90d

7.30a 0.219b 0.17a 840a 36a 26a 2.18a 60a 451ab 7.52cd

7.31a 0.243b 0.23b 887b 37a 28a 2.29ab 74b 513b 6.93c

7.33a 0.336c 0.26b 892b 38ab 29ab 2.43b 113c 685c 6.06b

7.40ab 0.544d 0.27b 946c 42b 32b 2.52b 129cd 774d 6.0b

7.48b 0.766e 0.27b 1008d 43b 33b 2.90c 153d 819cd 5.35a


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