apatite nanoparticles act better and supply enough P nutrients to the plants compared to the soluble and solid counterparts. The greenhouse experiment conducted on soybean
(Glycine max (L.) Merrill) shows that applying of synthetic
apatite nanoparticles increases the growth rate (32.6%), seed
yield (20.4%), and biomass productions (above ground by
18.2% and below-ground by 41.2%) of the soybean. In this
experiment, apatite nanoparticles have been synthesized in
wet chemical route with carboxymethyl cellulose (CMC) as
stabilizing agent. The shape of the synthesized hydroxyapatite nanoparticles is spherical and particle size is 15 nm
approximately. Comparing to the regular P fertilizer (Ca
(H 2 PO 4 ) 2 ), the utilization of apatite nanoparticles improves
the yield and decreases the water eutrophication (Liu and Lal
2015a).
5.2 Carbon Nanomaterials
Carbon is one of the main elements required for the plants. It
is present in the all organic materials. Plants get the carbon
mainly from air in the form of carbon dioxide. Verma et al.
(2019) reported that the impacts of carbon nanomaterials on
plant growth (from enhanced crop yield to acute cytotoxicity) have been studied by many researchers. The concentration of the carbon nanomaterial is more important.
Vegetative growth and yield of fruit/seed increase at lower
concentration of carbon nanomaterials but they decrease at
higher concentrations of carbon nanomaterials. At lower
concentrations, carbon nanomaterials are able to increase
water uptake and transport, seed germination, and antioxidant activities (Verma et al. 2019). The supportive factors
available at lower concentrations of carbon nanomaterials
improve the vegetative growth and yield of fruit/seed.
Multi-walled carbon nanotubes (MWCNTs) are applied
with urea fertilizer for the growth of paddy plants. Functionalized carbon nanotubes are unique since they are
attached with a variety of functional groups on their surface.
This makes the carbon nanotubes material suitable for lots of
applications. MWCNTs are functionalized with 4wt% of
carboxyl (–COOH) functional groups. The functionalization
enhances the efficacy of urea fertilizer as plant nutrition for
(local MR219) paddy. About 0.6wt% of functionalized
MWCNTs is grafted onto urea fertilizer. The experiment is
performed using a pot under exposure to natural light. After
14, 35, and 55 days, the crop growth of plants significantly
increased. The homogeneous grafting of functionalized
MWCNTs onto the urea leads to such beneficial result
(Yatim et al. 2018). Functionalization of MWCNTs assists in
attaching urea fertilizer onto MWCNTs. The bonding
between urea and MWCNTs can be confirmed using spectroscopy and chemical characterization techniques such as
FT-IR and total N analysis. The functionalization process
facilitates the separation of nanotube bundles into individual
tubes (Yatim et al. 2015).
Carbon nanotubes (CNTs) are synthesized in chemical
vapor deposition (CVD) method. Zaytseva and Neumann
(2016) have explained the synthesis and applications of
carbon nanomaterials. Figure 6a shows the CVD reactor that
has reaction chamber and tubes (for inert gas and hydrocarbon supply). Figure 6b, c exhibits the base-growth and
tip-growth mechanism of CNT growth. Figure 6d enumerates the agricultural and environmental applications of
carbon-based nanomaterials (Zaytseva and Neumann 2016).
Generally, in SWCNTs production, methane gas is utilized
and the substrate is heated up to 850–1000 °C. In the case of
MWCNTs production, ethylene or acetylene gas is utilized
and the substrate is heated up to 550–700 °C. Carbon is
produced due to thermal decomposition of hydrocarbons.
After producing a certain concentration of carbon,
semi-fullerene cap is formed. In the next stage, the growth of
cylindrical nanotube is formed by carbon flow from the
hydrocarbon source on the catalyst (Matsuzawa et al. 2014;
Morsy et al. 2014). Formation of semi-fullerene cap and
cylindrical nanotube growth can be seen in Fig. 6b, c.
Nanoparticles can be used as potential plant growth
regulator. Preparation of the slow releasing Cu–Zn
micronutrient carrying carbon nanofibers (CNFs) is an easy
method. It can be done through dispersing the micronutrient
(Cu–Zn/CNFs) in a polymeric formulation of PVA–starch.
Applying the prepared micronutrient increases the plant
height significantly. The translocation of the Cu–Zn/CNFs
from roots to shoots is analyzed. Scavenging of reactive
oxygen species by the micronutrient nanoparticles is confirmed by measuring the quantity of superoxide anion radicals and hydrogen peroxide present in the plant (Kumar et al.
2018).
Banana peel pieces have been blended with tap water
using a high-speed mechanical blender which is then mixed
with potassium hydroxide. The prepared slurry has been
heated at 100 °C for 30 min (Fig. 7a). This thermo-chemical
process leads to produce the nanofertilizer. Figure 7b shows
the TEM image of the nanofertilizer. Figure 7c shows the
histogram analysis of the particles. The average particle size
of nanofertilizer is found to be 40 nm. Elemental analysis
reveals that chelated potassium, chelated iron, urea, citric
acid, amino acids, protein, and tryptophan are the some
materials present in the nanofertilizer. This nanofertilizer can
be applied to increase the germination of seeds in crops such
as tomato and fenugreek (Hussein et al. 2019).
Banana peel consists of Na
+ , K
+
, P, Ca
++
, Fe
+++ , and
Mg
++
. Mixing of potassium hydroxide with banana peel
helps to break lignin and cellulose. Presence of urea, citric
acid, amino acids, tryptophan, and protein liberate minerals.
It leads to the plant germination efficiently (Aboul-Enein
et al. 2016). Graphene oxide helps to release the potassium
140
T. Thirugnanasambandan
(Glycine max (L.) Merrill) shows that applying of synthetic
apatite nanoparticles increases the growth rate (32.6%), seed
yield (20.4%), and biomass productions (above ground by
18.2% and below-ground by 41.2%) of the soybean. In this
experiment, apatite nanoparticles have been synthesized in
wet chemical route with carboxymethyl cellulose (CMC) as
stabilizing agent. The shape of the synthesized hydroxyapatite nanoparticles is spherical and particle size is 15 nm
approximately. Comparing to the regular P fertilizer (Ca
(H 2 PO 4 ) 2 ), the utilization of apatite nanoparticles improves
the yield and decreases the water eutrophication (Liu and Lal
2015a).
5.2 Carbon Nanomaterials
Carbon is one of the main elements required for the plants. It
is present in the all organic materials. Plants get the carbon
mainly from air in the form of carbon dioxide. Verma et al.
(2019) reported that the impacts of carbon nanomaterials on
plant growth (from enhanced crop yield to acute cytotoxicity) have been studied by many researchers. The concentration of the carbon nanomaterial is more important.
Vegetative growth and yield of fruit/seed increase at lower
concentration of carbon nanomaterials but they decrease at
higher concentrations of carbon nanomaterials. At lower
concentrations, carbon nanomaterials are able to increase
water uptake and transport, seed germination, and antioxidant activities (Verma et al. 2019). The supportive factors
available at lower concentrations of carbon nanomaterials
improve the vegetative growth and yield of fruit/seed.
Multi-walled carbon nanotubes (MWCNTs) are applied
with urea fertilizer for the growth of paddy plants. Functionalized carbon nanotubes are unique since they are
attached with a variety of functional groups on their surface.
This makes the carbon nanotubes material suitable for lots of
applications. MWCNTs are functionalized with 4wt% of
carboxyl (–COOH) functional groups. The functionalization
enhances the efficacy of urea fertilizer as plant nutrition for
(local MR219) paddy. About 0.6wt% of functionalized
MWCNTs is grafted onto urea fertilizer. The experiment is
performed using a pot under exposure to natural light. After
14, 35, and 55 days, the crop growth of plants significantly
increased. The homogeneous grafting of functionalized
MWCNTs onto the urea leads to such beneficial result
(Yatim et al. 2018). Functionalization of MWCNTs assists in
attaching urea fertilizer onto MWCNTs. The bonding
between urea and MWCNTs can be confirmed using spectroscopy and chemical characterization techniques such as
FT-IR and total N analysis. The functionalization process
facilitates the separation of nanotube bundles into individual
tubes (Yatim et al. 2015).
Carbon nanotubes (CNTs) are synthesized in chemical
vapor deposition (CVD) method. Zaytseva and Neumann
(2016) have explained the synthesis and applications of
carbon nanomaterials. Figure 6a shows the CVD reactor that
has reaction chamber and tubes (for inert gas and hydrocarbon supply). Figure 6b, c exhibits the base-growth and
tip-growth mechanism of CNT growth. Figure 6d enumerates the agricultural and environmental applications of
carbon-based nanomaterials (Zaytseva and Neumann 2016).
Generally, in SWCNTs production, methane gas is utilized
and the substrate is heated up to 850–1000 °C. In the case of
MWCNTs production, ethylene or acetylene gas is utilized
and the substrate is heated up to 550–700 °C. Carbon is
produced due to thermal decomposition of hydrocarbons.
After producing a certain concentration of carbon,
semi-fullerene cap is formed. In the next stage, the growth of
cylindrical nanotube is formed by carbon flow from the
hydrocarbon source on the catalyst (Matsuzawa et al. 2014;
Morsy et al. 2014). Formation of semi-fullerene cap and
cylindrical nanotube growth can be seen in Fig. 6b, c.
Nanoparticles can be used as potential plant growth
regulator. Preparation of the slow releasing Cu–Zn
micronutrient carrying carbon nanofibers (CNFs) is an easy
method. It can be done through dispersing the micronutrient
(Cu–Zn/CNFs) in a polymeric formulation of PVA–starch.
Applying the prepared micronutrient increases the plant
height significantly. The translocation of the Cu–Zn/CNFs
from roots to shoots is analyzed. Scavenging of reactive
oxygen species by the micronutrient nanoparticles is confirmed by measuring the quantity of superoxide anion radicals and hydrogen peroxide present in the plant (Kumar et al.
2018).
Banana peel pieces have been blended with tap water
using a high-speed mechanical blender which is then mixed
with potassium hydroxide. The prepared slurry has been
heated at 100 °C for 30 min (Fig. 7a). This thermo-chemical
process leads to produce the nanofertilizer. Figure 7b shows
the TEM image of the nanofertilizer. Figure 7c shows the
histogram analysis of the particles. The average particle size
of nanofertilizer is found to be 40 nm. Elemental analysis
reveals that chelated potassium, chelated iron, urea, citric
acid, amino acids, protein, and tryptophan are the some
materials present in the nanofertilizer. This nanofertilizer can
be applied to increase the germination of seeds in crops such
as tomato and fenugreek (Hussein et al. 2019).
Banana peel consists of Na
+ , K
+
, P, Ca
++
, Fe
+++ , and
Mg
++
. Mixing of potassium hydroxide with banana peel
helps to break lignin and cellulose. Presence of urea, citric
acid, amino acids, tryptophan, and protein liberate minerals.
It leads to the plant germination efficiently (Aboul-Enein
et al. 2016). Graphene oxide helps to release the potassium
140
T. Thirugnanasambandan