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Carbon nanoparticles in ‘biochar’boost wheat
(Triticum aestivum) plant growth
Manav Saxena, Sheli Maity and Sabyasachi Sarkar*
Biochar is shown to contain raw carbon nanoparticles (rCNPs). The traditional use of biochar for the healthy
growth of plants is due to its retention capability of nutrients for needs-based slow release. On aging, the
rCNPs are aerially oxidized with the incorporation of hydrophilic carboxylic and hydroxyl groups on the
biochar surface to increase its spongy structure that enhances its absorptivity to water and several ionic
nutrients. The chemical oxidation of rCNPs in biochar introduces similar carboxylic acid and hydroxyl
groups in transforming rCNPs to water soluble carbon nanoparticles (wsCNPs). These wsCNPs in
solution enhance the growth rate of wheat plants. The concentration of wsCNPs used in this wheat plant
growth study varied in the range from 10 to 150 mg L
1
. The seeds treated with wsCNPs in this range
showed higher growth rates, with the optimum growth found to occur with 50 mg L
1
wsCNPs, as
compared with the control study. This suggests a concentration threshold of wsCNPs for the optimum
stimulation of plant growth that the aged biochar can readily meet. Model experiments with ammonium
nitrate as cationic and anionic nutrients show that both the rCNPs and wsCNPs hold the nutrient ions,
although the negatively charged wsCNPs hold less effectively than the anionic nitrate. These carbon
nanoparticles are capable of releasing cationic and anionic nutrients slowly over time. Such action is
correlated with the booster action of CNPs in supplying nutrients to the young plants. Thus, wsCNPs
may be a better choice than fertiliser or manure alone, due to the controlled and slow release of
nutrients for better assimilation by plants.
1. Introduction
Carbon is one of the most key elements involved in fostering
life. In addition to its existence in organic compounds respon-
sible in biochemical processes, elemental carbon in its newer
nano version, excluding coal, graphite or diamond, has gained
added importance in several applications.
1
The story of such
carbon is related with some spectacular discoveries but also
with issues such as carbon balance to global warming and
climate change.
2
Biochar‡is a carbonized form of leover biomass (waste
stems and roots) in agricultural land, obtained by its pyrolysis
under limited air. This is mixed with the soil during ploughing
of the land for the next crop to enhance the fertility of the land.
Smaller particles of carbon in the nano range are formed during
biochar synthesis. These particles are called biochar dust, due
to their smaller sizes.
3a
The land of the Amazon basin ‘terra
preta’is highly fertile owing to the high quantity of carbon as
biochar, formed by carbonization processes over a long period
of time.
3
The carbon in biochar does not degrade readily and
stays in the soil for several years. However, on aging, the defects
on the surface of the carbon in biochar responds to a slow aerial
oxidation, with a resulting peripheral incorporation of hydroxyl
and carboxylic groups.
3d
The highly porous carbon in biochar
retains micro nutrients for controlled release, which is neces-
sary for germination and growth of the plants.
3
It can adsorb
water up to 4.5 times its dry weight, due to its porous structure,
which mitigates the drought effect.
4
Biochar applied in the soil
has been shown to retain these promoting effects when tested
for a short period of 2 years
3c,d
to longer periods, even up to a
hundred years of observation in ‘terra preta’of the Amazon
basin soil.
3b
Biochar in its crushed form increases its surface
area, which in turn enhances its effectiveness.
3d
Interestingly in
soil, the slow aerial oxidation of biochar on its surface helps to
enhance its ion exchange and nutrients retaining capacity.
3d,5a
Biochar is also well known to increase the colonization of
mycorrhizal, rhizobia.
3c
It is known that graphene units with
heteroatoms (N, O) are one of the main structural entities of the
biochar surface and are responsible for nutrients adsorptio-
n.
3a,5b
These graphene units curve to create spherical-like
carbon particles under thermal conditions.
5c–g
The pyrolysis of
carbonaceous materials thus rst generates graphene nucle-
ation from the pentagonal ring, followed by a spiral shell
growth, with the subsequent incorporation of pentagonal,
hexagonal and heptagonal rings to facilitate carbon nano-
particles growth.
5c–g
Department of Chemistry, Indian Institute of Engineering Science and Technology
Shibpur, Howrah 711103, West Bengal, India. E-mail: abya@iitk.ac.in; protozyme@
gmail.com; Tel: +91-33-266806464
Cite this: RSC Adv.,2014,4, 39948
Received 2nd July 2014
Accepted 7th August 2014
DOI: 10.1039/c4ra06535b
www.rsc.org/advances
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The effect of nanocarbons in plant growth is relatively less
explored compared with similar studies with the animal
kingdom.
6
Though specic uses of such carbon nanomaterials
have been carried out on different plant species, including
rice,
6a
gram,
6b–c
tobacco,
6d–e
and wheat.
6f
Earlier reports show
that single-walled carbon nanotubes (SWCNTs), multi-walled
carbon nanotubes (MWNTs), and carbon nano-onions (CNOs)
readily penetrate the biological membrane barriers in mam-
mals,
7a
plants,
6d
and also in microorganisms.
7b
It is also shown
that water soluble carbon nanotubes (wsCNTs) become aligned
due to an endo-osmotic root pressure in the xylem vessels of
plants, which then enhances the water and nutrients uptake
capacity.
6b,8
In the presence of carbon nanotubes (CNTs), lignin
biosynthesis
9
suggests the formation of more biomass of xylem
vessels than is shown to be directly related to the growth of the
overall plant, in relation to the biochar effect.
3
The essential
nutrients required for a plant interact with the hydrophilic
groups attached to the surface of the carbon nanomaterials by
hydrogen bonds and by electrostatic interaction in the outer
peripheries of CNPs
6
and remain attached there on a temporal
basis, and thus these carbon nanomaterials work as storage
houses for micronutrients. Such retention then allows a sus-
tained and slow release of these for the facile transport of the
essential nutrients inside the xylem vessels,
6
which is similar to
retaining the activity of biochar.
3d,5
The present work deals with the isolation of carbonaceous
materials from biochar as raw carbon nanoparticles (rCNPs). As
these are not effectively dispersible in water, the isolation of
water soluble carbon nanoparticles (wsCNPs) from the rCNPs of
biochar was carried out to compare its concentration dependent
effect in the growth of wheat (Triticum aestivum) plant. We
choose wheat for this study as it is the most important grain
used as a staple food throughout the world. Furthermore, we
show here that the surface groups on either rCNPs or wsCNPs
play an important role in determining the nature of the effec-
tively adsorbed ions by using nitrogen containing essential
nutrient ions. These adsorbed ions are subsequently released
slowly, in relation to the nutrient needs in the growth of young
plants.
2. Experiment
2.1 Materials
All chemical reagents were of analytical grade and used without
further purication. Water used in the control experiments, as
well as for wsCNPs, to make the solutions was simple tap water
to mimic the environmental conditions otherwise mentioned.
The tap water quality parameters are known.†
2.2 Synthesis of water soluble carbon nanoparticles
We collected ‘biochar’material produced by carbonization of
the plant waste lein rice agriculture elds used in the present
study. The ‘biochar’collected was powdered and the ne
powdered part was separated from the unburned parts by
sieving. The powdered material was treated with water and
stirred and then the stirring was stopped, whereby the heavier
part containing silica and the other solid inorganic materials
settled down fast, leaving the upper part containing oating
carbon particles, which were decanted off. Repetition of this
oatation procedure resulted in the separation of the essential
carbon materials in almost pure form from the silica and mud.
The carbon part was then ltered through a lter paper and
washed twice with water to remove any residual soluble salts
present therein. The carbon residue was then dried at 60 C for
5 hours. This carbon is termed as raw carbon nanoparticles
(rCNPs). The dried carbon material was treated with HNO
3
and
water (in a 1 : 1 ratio), for oxidation to produce the water soluble
version as reported earlier.
10,6b,c,11
The nal isolated and dried
water soluble carbon powder was used in the solution study and
termed as wsCNPs.
2.3 Surface disinfestation of seeds
The surface disinfestation of seeds was carried out by their
immersion in 10% sodium hypochlorite solution for 10 min
followed by washing three times with double-distilled water,
and then subsequently soaked in tap water†for control and in
wsCNPs solution of different concentrations for 6 h before
use.
6b,c,f
2.4 Preparation of wsCNPs solution and germination
For the optimization, different concentration (10, 20, 40, 50, 80,
100 and 150 mg L
1
) of wsCNPs were prepared as stock solution
and used in comparison with the control (without wsCNPs).
Though the dissolved wsCNPs remained in solution for an
extended period of time, even then each solution was shaken
well before use. For germination, the wsCNPs-treated wheat
seeds were placed in cotton clothes of one square feet size
soaked with the respective concentration of wsCNPs and, for
control, under water for comparison. Cotton clothes were
wetted using the same volume of respective solutions. Seeds
covered with such wet cotton clothes were placed in polystyrene
plates during the germination period.
2.5 Treatment of soil
Natural soil was taken and dried at 60 C for 10 h to remove any
excess water from it and any volatile substances, if present.
Then, it was allowed to cool to attain room temperature. The
weighed amount of soil placed in each earthen pot was xed to
culture the wheat samplings under similar conditions aer
germination under moist clothes.
2.6 Wheat plant growth
On the 5th day, the germinated wheat seeds were transferred
into the soil and placed in different earthen pots with the
†pH ¼7.3; total dissolved solids (mg L
1
)¼495; hardness (as CaCO
3
)(mgL
1
)¼
160; alkalinity (as CaCO
3
)(mgL
1
)¼310; nitrate (mg L
1
)¼0.59; sulfate (mg L
1
)
¼51; uoride (mg L
1
)¼0.69; chloride (mg L
1
)¼235; turbidity (NTU) ¼0.2;
arsenic (mg L
1
)¼0.002; copper (mg L
1
)¼BDL; cadmium (mg L
1
)¼BDL;
chromium (mg L
1
)¼0.002; lead (mg L
1
)¼BDL; iron (mg L
1
)¼0.276; zinc
(mg L
1
)¼BDL; fecal coliform (cfu) ¼0; E. Coli (cfu) ¼0. [BDL ¼below
detection limit].
‡http://www.theguardian.com/commentisfree/2009/mar/27/biochar.
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germinated seeds placed under the same depth of the soil in
each pot, and then allowed to grow in an open environment.
2.7 Characterization
The surface morphologies of rCNPs and wsCNPs were imaged
using a eld emission scanning electron microscope (FESEM),
which is a SUPRA 40VP (Carl Zeiss NTS GmbH, Oberkochen,
Germany) in high-vacuum mode operated at 5 kV. Transmission
electron microscopy (TEM) analysis was performed using a
Tecnai 20 D456 U-Twin Gun W, HT 200 kV. 400 mesh size
carbon coated copper grid procured from Electron Microscopy
Sciences, Hateld, PA, was used for the TEM study. FT-IR
spectra were recorded with a Bruker Vertex 70 FT-IR spectro-
photometer as pressed KBr pellets. The samples were prepared
using standard protocols.
2.8 NH
4+
and NO
3
ions release study
Nitrogen containing ions are some of the main ingredients of
fertilizer and these essential nutrients are required for plant
growth and were thus chosen for this study. Nitrogen de-
ciency leads to chlorosis (yellowing) of plant leaves, due to the
drop in chlorophyll content. In a typical loading procedure,
200 mg of CNPs (both versions) was packed in a glass column
of inner diameter 3 mm over a glass wool support. 20 mL of
10
4
MNH
4
NO
3
solution was poured gently in to the top of the
column and was leundisturbed to attain equilibrium for 12
h. The solution was then eluted through the column with an
appropriate ow rate of 0.25 mL min
1
.Thisrst recovered
elute was tested for NH
4+
by Nessler's reagent
12
and NO
3
ion
by Griess–Ilosvay reagent under reduction with Zn dust.
10
The
un-adsorbed NH
4+
/NO
3
ions were quantied by using a
JASCO V-530 UV-Vis spectrophotometer, following standard
spectrophotometric methods of analyses. The column was
then quickly washed with a portion of chilled water (15 mL),
and then dried at 60 C under a current of N
2
gas through the
column.
To understand the subsequent time-bound NH
4+
and NO
3
ion release, distilled water was added in the top of the column
and it was eluted with a xed ow rate (0.25 mL min
1
)at
intervals of 24, 72, 120, 168 and 240 h. A xed volume of the
elute in each of these time periods was taken and the concen-
tration of NH
4+
and NO
3
ions released were spectrophot-
metrically evaluated using the Nessler test
12b
and Griess–Ilosvay
reagent with Zn dust.
10
Similar experimental procedures were
followed for both the rCNPs and wsCNPs forms.
3. Results and discussions
The carbon separated from the mud part from biochar, rCNPs,
was imaged by FESEM and TEM microscopy and is shown in
Fig. 1a and b. Once this is derivatized, the solubility pattern of
wsCNPs can be seen, as in Fig. 3. The surface visualizations of
wsCNPs were achieved by FESEM and TEM as shown in Fig. 1c
and d. The nearly spherical morphologies of wsCNPs are
conrmed by TEM (Fig. 1d). High resolution transmission
electron microscopy (HRTEM) shows the multiwall, porous
nature of wsCNPs (Fig. 3) and thus these can best be described
as carbon nano-onions.
6c
FESEM and TEM clearly show the
presence of carbon nanoparticles in the size ranges from 20 to
50 nm (histogram not shown). These wsCNPs contain an
average of 20% of carboxylic groups attached (by weight), as
found by acid–base titration.
13
Extensive surface impregnation
of the carboxylic acids and other enol groups make the outer
surface of these wsCNPs porous. Initially, to dissolve this in
water, sonication for a few minutes is essential. These wsCNPs
remain in solution for a minimum period of 30 5 days in
water (Fig. 2).
Fig. 1 FESEM and TEM images of biochar: (a and b) rCNPs; (c and d)
wsCNPs.
Fig. 3 From left to right: control, 10, 50, 80 and 150 mg L
1
solutions
of wsCNPs in water.
Fig. 2 HRTEM image of wsCNPs.
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The FTIR of rCNPs and wsCNPs are shown in Fig. 4, which
shows that these retain almost similar functional groups.
The FTIR of rCNPs and wsCNPs show peaks around 1700 and
3420 cm
1
, corresponding to the vibration due to the presence
of >C]O and –OH groups, respectively. As expected for rCNPs,
the carboxyl stretching vibration (appearing only as the
shoulder) is related to the low abundance of carboxylate
groups compared to that in wsCNPs, where the peak at
1717 cm
1
becomes prominent. The prominent peak around
1100 cm
1
is responsible for the presence of –C–O(H) vibrations
and originates from hydroxyl groups attached in both the
forms. This conrms the presence of hydrophilic groups on
the surface of rCNPs
3d,5a
introduced by ageing and, for wsCNPs,
the density of carboxylation is increased due to the oxidative
treatment to enhance its solubility in water.
It was found that wsCNPs-exposed wheat seeds germinate
faster than the control, which is consistent with previous
reports.
6
The optical images of germinated seeds for different
sets of wsCNPs and control are shown in Fig. 5. Aer trans-
ferring the germinated seeds into the soil, we monitored the
length of the shoot part of the wheat plants in every three day
intervals. The shoot length of the control and wsCNPs-treated
plants at intervals are graphically represented in Fig. 6. The
shoot lengths of wheat plants increase in a proportional
manner with 10–50 mg L
1
concentration of wsCNPs. When
80 mg L
1
of wsCNPs was used, the growth of the shoot length
slightly decreased compared to that achieved under 50 mg L
1
treated wsCNPs. However, this is higher than that for 40 mg L
1
treated wsCNPs. The percentage shoot growths of wsCNPs-
treated seeds with respect to the control seeds were calculated
with the standard equation, and the results obtained are pre-
sented in Fig. 7.
Shoot growth %¼
LwsCNPs Lcontrol
Lcontrol
100
where L
control
and L
wsCNPs
are the shoot lengths for the control
and wsCNPs-treated seeds, respectively.
Fig. 5–7 conrm that the growth of the shoot part of the
wheat plants increase in the presence of wsCNPs compared to
that with the control. The shoot lengths of wsCNPs-treated
wheat plants are signicantly longer compared with the
control in the concentration range of 10–80 mg L
1
. In the range
of 100–150 mg L
1
of wsCNPs, the growth remains similar to the
seeds treated with 10 mg L
1
of wsCNPs (Fig. 6).
These results clearly indicate that the growth rate of the
wheat plants treated with 50 mg L
1
is optimum in comparison
with the growth obtained from the other concentration of the
wsCNPs used. The growth rate of wheat plant exposed with an
80 mg L
1
concentration of wsCNPs lies in between those found
Fig. 4 FTIR of rCNPs (red) and wsCNPs (black).
Fig. 5 Germinated seeds (a) control; with wsCNPs of concentration
(b) 10 mg L
1
; (c) 20 mg L
1
; (d) 40 mg L
1
; (e) 50 mg L
1
; and (f)
150 mg L. (These are not imaged from the same distance and the
figures compare only the variation of the shoots in the germination).
Fig. 6 The growth of the control and wsCNPs-treated wheat plants.
Fig. 7 The growth difference in the shoot length of wsCNPs-treated
and the control seeds with respect to the control seeds (in %).
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under exposure with 40 and 50 mg L
1
(Fig. 6 and 7). Therefore,
the optimum concentration of wsCNPs as a growth stimulator
may lie in the range of 40–80 mg L
1
, and preferably around
50 mg L
1
. Moreover, it has been shown earlier that the carbon
nanomaterials enhance the overall growth of the plants.
3c,d,6
If
transport and the release of micronutrients is the exclusive task
of this growth simulator, then it may be that going beyond the
threshold, an excess supply of mineral nutrients may be dele-
terious to the plant and may retard its growth. It is to be noted
that these carbon nanomaterials remain in the root section of
the plant and do not travel to the higher shoot part, and thus the
possibility for the distribution of these carbon nanomaterials in
the products from such treated crops may not be there.
6e,f
It is
true that no apparent distinction between the grains obtained
using biochar or without its use can be made. The consumption
of crops under biochar treatment over an extended period for
several centuries do not show any ill effects due to the genera-
tion of human habituation with the consumption of such
products. We have recently shown that the human race has
achieved immunity from nanocarbon materials by the invol-
untary intake of such products with cooked food for centuries.
14
As the use of biochar is an age old practice, so any distribution
of such wsCNPs/rCNPs inside seeds or fruits on consumption
may have developed immunities in humans.
The average size of root cells is roughly 1000 times larger
than the diameter of wsCNPs (20–50 nm). These wsCNPs/rCNPs
are known to get into plant roots and nally become embedded
into the xylem vessels, as previously shown by us using electron
microscopic studies.
6c,d
The porous nanoparticles hold the
nutrients and are the active constituents of biochar,
3d,5
which we
show slowly release the mineral nutrients like ammonium and
nitrate ions. The presence of carbon nanomaterials inside the
xylem vessels enhances the water uptake and transportation, by
a channel process or by adsorption process.
6b
With the higher concentration of wsCNPs, the decrease in
the growth and growth rate of wheat plants (Fig. 6 and 7) is an
important inference, and which indicates that the optimized
concentration of wsCNPs should be used in relation to their
application as growth promoters. At higher concentrations of
wsCNPs, the easy release of micro/macronutrients into the root
site accumulate and increase in quantity, which may have a
deleterious effect on the plant growth. Thus the rCNPs which
cause biochar to be much less soluble in water have an advan-
tage over wsCNPs, so far as their intimate association with the
root of the plant. Therefore, biochar has the optimum capability
to supply nutrients for the growth of plant. The difference
between crops using fertilizers and manures based on biochar
farming may be addressed in the following context. Biochar, by
holding essential nutrients, slowly releases these need-based
nutrients to a plant for its normal healthy growth in contrast to
fertilizer treatment, where fertilizers rapidly release these
mineral nutrients and can cause cytotoxicity in a plant, result-
ing in senescence. Thus, the sprinkling of fertilizer could supply
such nutrients for growth access at the initial stages but could
ultimately cause death of the plant. Frequently, excess watering
is done in the eld to wash away the local excess concentration
of the fertilizer aer a few days of its sprinkling, resulting in
draining out of these essential nutrients and their percolating
through the top soil layers and accumulating underground. To
avoid this happening, expensive fertilizers are nowadays avail-
able that are wrapped in bioaccessible synthetic polymers that
slowly releases micronutrients, similar to what one can simply
achieve using biochar.
It is known that the dehydrogenase activity is associated with
the ability of roots to retain nutrients and water, which is
dependent on the concentration of these carbon nano-
materials.
15
The decrease in dehydrogenase activity with higher
concentrations of carbon nanomaterials has also been repor-
ted.
6f
However, in contrast to the previous report,
6f
we have
observed the enhancement in the shoot length of the wheat
plants. In the present case, plant roots are allowed to penetrate
the soil layers to grow under normal conditions, which
remained absent in the case study under the articial growth
media.
6f
In addition, it is expected that soil provides the
optimum environment for the growth of the roots. It has also
been shown that the root growth is affected in articial growth
media, causing artefact responses.
16
3.1 NH
4+
/NO
3
ions release study
Fertilizers like NH
4
NO
3
provide NH
4+
and NO
3
ions to the
plants as essential nutrients for their growth. These ions enter
through the xylem vessels of plants. CNPs, due to their much
smaller sizes, enter into the xylem vessels and help the plant by
adsorbing essential ions and water.
6b,c
Interestingly, such ions
are also adsorbed by biochar present in the soils. The carbon
nanomaterials in the xylem vessels have electrostatic interac-
tions with the essential ions, and this thus leads to adsorption
on the surface.
3,6b,c,f
In a typical experiment, the slow release of
adsorbed NH
4+
and NO
3
from rCNPs and wsCNPs are shown in
Fig. 8 Release of adsorbed ions from rCNPs and wsCNPs at different
time intervals: (a) NH
4+
; (b) NO
3
ions.
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Fig. 8. It is interesting to note that the surface groups play
diverse roles in the ions being absorbed by these CNPs. The
rCNPs, with very limited aerial oxidized surfaces, adsorb both
the ions, as shown in Fig. 8. In the case of wsCNPs, where the
surface is highly negatively charged due to the presence of more
carboxylic acid and hydroxyl groups, NH
4+
ions are adsorbed
preferably over NO
3
ion by wsCNPs (Fig. 8) as compared to r-
CNPs. The chemical complexity of wsCNPs may allow adsorbing
NO
3
ions, although to a much lesser extent compared to that
with the adsorption of rCNPs. Interestingly, its adsorption
capability has been judged qualitatively for several other cations
like potassium, calcium, and nickel as noteworthy, as all these
are essential mineral nutrients known for plant growth. Thus,
biochar can help to serve several other mineral nutrients
needed for the healthy growth of a plant. Such adsorption and
desorption of NH
4+
and NO
3
may be similar for other ions,
albeit the rates may differ, and may even continue in cycles, as
biochar is stable for years and only slowly is oxidised by air on
its surface.
3c,d,5
Therefore, our investigation conrms that, on
aging, the aerial oxidation of biochar may function like wsCNPs
as described herein. The role of biochar is even more important
to trap both the anionic and cationic forms of nutrient ions,
followed by their slow delivery as required by the plant for
growth.
3,6b,c,f
4. Conclusions
The present work is intended to understand the science behind
the age old use of ‘biochar’in the agriculture eld to increase
crop productivity. We show that biochar is essentially
comprised of surface defective carbon nanoparticles, which on
aerial exposure with aging may be oxidized, thus incorporating
carboxylated and hydroxylated groups to form the water soluble
version of carbon nanoparticles. These functional groups, along
with the porous structure of such biochar, readily trap several
essential mineral ions. The slow and timely release of these
mineral nutrients is optimally used in enhancing the growth of
wheat plant under natural conditions. We show that there is a
concentration threshold and that exceeding this may be related
to the supply of extra nutrients causing harm in the growth of
the plant. The rCNPs in biochar work to nurse the young sapling
with the slow release of essential nutrients in a sustained
manner. The use of fertilizer may have the effect of a localized
high dose delivery of these elements, which could ultimately
cause plant senescence and even death. Biochar in a sense
works as a promoter or booster, by retaining the essential
elements from the organic manure or from the synthetic
fertilizer applied in the soil, for the controlled supply of the
optimised mineral nutrients to the plant for its normal growth.
In addition it retains water which it may provide to the thirsty
plant sapling during the absence of water and especially in the
arid zone. This helps the optimal use of fertilizer or manure and
prevents these from being wasted, by retaining the nutrients for
sustained release. Therefore, more detailed research work could
be possible to relate its role in conjunction with the optimal use
of manure and/or fertilizer for the growth of a plant. It is to be
noted that the use of nano carbons in the form of ‘biochar’over
prolonged ages does not show any adverse effects on human
health.
Acknowledgements
M.S. thanks the University Grant Commission, New Delhi,
India, for UGC-Dr D.S. Kothari Postdoctoral fellowship. S.M.
thanks University Grant Commission, New Delhi, India, for
Junior Research Fellowship. S.S. thanks the Department of
Science and Technology, New Delhi, India, for Ramanna
Fellowship.
Notes and references
1 D. Jariwala, V. K. Sangwan, L. J. Lauhon, T. J. Marksa and
M. C. Hersam, Chem. Soc. Rev., 2013, 42, 2824.
2 http://scienceprogress.org/2008/07/interview-carbon-age/.
3(a) F. G. A. Verheijen, S. Jeffery, A. C. Bastos, M. van der Velde
and I. Diafas, in Biochar Application to Soils –A Critical
Scientic Review of Effects on Soil Properties, Processes and
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