Introduction
The problem of soil pollution with toxic heavy metals
has enormously increased which pose several environmental and health issues.
Heavy metals are accrued in soils by natural and anthropogenic sources such as
mining activities, weathering, domestic and industrial effluents and frequent
use of fertilizers and pesticides in agriculture (Moon et al. 2013). Mostly, the heavy metals are non-biodegradable in
nature and their occurrence in the environment and ecosystem is a main concern
for healthy and safe environment (Qadir et
al. 2013).
Cadmium (Cd) is non-essential,
trace, toxic heavy metal and is hazardous at < 1 mg kg-1 soil
(WHO 2000). It is gradually accumulated in plants’ edible and non-edible parts
and continuous exposure can cause various acute and chronic health problems
such as kidney, prostate diseases, lungs cancer and can damage the pulmonary
and skeletal system in humans (IARC 2012). The toxicity of Cd in soil also has
detrimental effects on plant yield due to decreased germination and plant growth
and development (Hassan et al. 2016;
Naeem et al. 2016). The plants uptake
Cd with uptake of minerals nutrition’s and Cd translocation in plants tissues
results in chlorosis and necrosis of leaves, inhibition of photosynthetic
pigments, ultimately resulting in stunted plant growth and reduced food quality
(Metwally et al. 2005). Cadmium
stress may also severely affect the chlorophyll and carotenoid contents (Chen et al. 2014), transpiration rate, and
stomatal conductance in plants (Shafi et al. 2011).
To overcome the hazards of the heavy metal toxicities in
environment, various strategies have been adopted including the inorganic and
organic soil additives (Yousaf et al.
2016). Among the organic soil amendments, biochar is carbon rich organic soil
amendment (Wardle et al. 2008; Farooq
et al. 2020a). In a study,
application of biochar to low fertile sandy soil enhanced the soil carbon
(7–11%), phosphorus 68–70% and potassium 37–42%, in comparison with control (no
biochar addition) (Laghari et al. 2015).
In another study, wheat straw derived biochar greatly promoted the nitrogen,
phosphorus and potassium availability in poor fertile acidic soil (Zhang et al. 2017). Mostly, the biochar has
high pH, cation exchange capacity (CEC) and had more surface area and comprises
of well-designed structures of micro-porous and active efficient functional
groups (Rajapaksha et al. 2016; Hussain et al.
2017). Biochar could be more useful for long term carbon sequestration in soil
(Yousaf et al. 2016). Moreover,
biochar improves the soil health, physical and chemical properties, soil
fertility and nutrient retention by adding potassium, sodium, magnesium and
calcium for plants (Hussain et al.
2017; El-Naggar et al. 2019; Minhas et al. 2020). Biochar has capacity to
remediate metals toxicities from soil and reduce their uptake and translocation
in plants (Lu et al. 2014). The
addition of biochar works as pollutant premeditator in heavy metals
contaminated soil (Park et al. 2011)
and remediate the metal toxicity form soil particles by raising soil pH (Zeng et al. 2011).
Addition of biochar reduces the metal mobility by
reducing metals phytotoxicities and translocation in plants grown in polluted
soil (Lu et al. 2014; Hussain et al. 2017). In a study, the addition
of rice (Oryza sativa L.) straw and bamboo derived biochar induced the
Cu, Zn, Pb and Cd immobilization in polluted soil by reducing heavy metals
uptake in plants (Lu et al. 2017).
Addition of biochar potentially reduces the Cd bioavailability in wheat as
compared to farmyard manure, compost and press mud (Yousaf et al. 2016). The maximum Cd reduction (< 0.2 mg kg-1)
in plants edible parts is compulsory for safe food production in polluted soil
(Rizwan et al. 2016a) to ensure healthy
human life. Biochar has potential to reduce the hazards of Cd toxicities in
plants including rice (Bian et al. 2013), rapeseed (Brassica napus L.)
(Shaheen and Rinklebe
2015), wheat (Yousaf et al. 2016) and
spinach (Spinacia oleracea L.) (Younis et al. 2016). The maximum reduction of Cd toxicity in various parts
of plants due to lowered Cd concentration in pore water or induced Cd binding
with organic matter after biochar addition (Lu et al. 2017).
Worldwide, bread wheat (Triticum aestivum L.) is widely cultivated food
crop with annual yield of almost 761 million tons (FAO 2020). Wheat occupying central position in Pakistan agriculture and
have significant place among cereals. The plants mostly uptake metals
through roots and then translocated towards shoots and grains (Naeem et al. 2016). The excess of Cd decreases
the plant growth and development by disturbing the photosynthesis process and
interrupt mineral nutrition’s in wheat (Rizwan et al. 2016a). Therefore, it is important to find out eco-friendly,
cheap, and effective alternatives to remediate the Cd toxicity in polluted
soils for the successful and safe cultivation of food crops on sustainable
basis. Previously, a limited work has been reported to compare the efficiency
of biochar produced from various feedstocks to immobilize Cd in alkaline
polluted soil by reducing metal phytotoxicity in wheat. For this study, we
hypothesized that biochar may enhance wheat growth and yield by reducing Cd
hazards in polluted alkaline soil. The specific objective of this study was to
evaluate the relative amendment impact of applied biochar for Cd immobilization
in contaminated soil and its impact of wheat growth and yield.
Materials and Methods
Soil collection
and analysis
The cultivated soil was collected (0–20 cm) from
Experimental Research area of College of Agriculture, Bahadur Sub-Campus Layyah of Bahauddin Zakariya University
Multan, Pakistan. The soil was air dried, crushed and sieved (2 mm) and
then was brought to laboratory for further analysis. The physio-chemical
characteristics of tested soil are presented in Table 1. The soil texture and
organic matter were measured by Hydrometer method (Day 1965) and Walky and Black method (Walkely
and Black 1934), respectively. Soil pH and electrical conductivity (EC) were
analyzed with pH meter (PHS-1701, China) and EC meter (CD-350, China) by using
soil to water ratio of 1:1 (w/w).
Moreover, soil nitrogen, available potassium and phosphorus were measured and
values are described in Table 1.
Preparation of biochar
Feedstock’s, poultry manure, sugarcane press mud, and
farmyard manure, were chosen for biochar preparation on their extensive
availability. Sugarcane press mud was obtained from nearby Layyah Sugar Mills
Limited Layyah, while the poultry manure and farmyard manure were obtained from
suburb of Layyah city, Pakistan. No special approval was required to collect
experimental material and to conduct experiment. All soil amendments were
individually managed during shade drying and handling. Before biochar preparation,
Cd contents were analyzed from each feedstock. Briefly, 0.5 g of each feed
stock was added di-acids mixture H2SO4–H2O2
and stay overnight in fume hood. The samples were digested on hotplate until
clear liquor obtained and then filtered and diluted with distilled water. The
prepared samples were analyzed for Cd determination by using atomic absorption
spectrophotometer (Agilent AA-240FS Varian, U.S.A.). The obtained Cd values
from each feedstock’s were found to be safe (Cd < 0.001 mg kg-1)
for experimental use. Biochar was prepared by pyrolysis of each feedstock under
minimal oxygen condition according to methods detailed in Rizwan et al. (2016b). Briefly, desired
material (5 g) was placed in ceramic crucibles and covered with lid and placed
in laboratory muffle furnace and temperature was adjusted to 400°C and
pyrolysis for 4 h after constant temperature was obtained. The prepared biochar
was grinded and sieved (2 mm) for experimental use. The pH of poultry manure
derived biochar was 10.4, farmyard manure 10.8 and sugarcane press mud 10.2,
while electrical conductivity of these biochar were 4.6, 4.9, and 4.5 ms cm-1, respectively.
Pot experiment
The soil was synthetically polluted with Cd 5 mg kg-1
of soil (highly toxic) and applied by dissolving CdNO3.4H2O
in deionized water and then incubated for one month. The contaminated soil was
amended with biochar derived from poultry manure (PM), farmyard manure (FYM)
and sugarcane press mud (PS) with various levels and mixed thoroughly except
control (only Cd contaminated soil) and further incubated for 60 days (60%
moisture). The soil moisture contents were carefully maintained for each pot on
weekly basis and the reduction of water difference was maintained by adding
water to each pot according to the calculation (Reeuwijk 2002).
%201633-1640_files/image002.png){kind=small}
Each earthen pot (40 cm × 20 cm) was filled with 5.5 kg
of amended soil. The treatments were control (only Cd polluted soil), PM-5 (2.5
g kg-1), PM-10 (5 g kg-1), FYM-5 (2.5 g kg-1),
FYM-10 (5 g kg-1), PS-5 (2.5 g kg-1), PS-10 (5 g kg-1).
No amendment was applied in control treatment. The soil was contaminated with
Cd on 15 August 2017 and after one month of contamination, biochar treatments
were applied on 15 September 2017. After two months of biochar application,
wheat seeds were sown on 16 November 2017. The experiment was arranged by
following complete randomized design (CRD) and each treatment was replicated
thrice. There were three pots in each replication. In each pot, ten wheat seeds
of wheat cultivar Galaxy-13 were sown and after germination five plants were
maintained in each pot. Recommended fertilizers nitrogen 90 mg kg-1,
phosphorus 81 mg kg-1, and potassium 69 mg kg-1 per pots
were applied from urea, di-ammonium phosphate and sulphate of potash,
respectively in each pot (Agricultural Department Punjab, Pakistan www.agripunjab.gov.pk).
The pots were placed in open environmental conditions. The pots were uniformly
irrigated to avoid drought stress. The plants from each pot were harvested at
maturity on May 01, 2018.
Agronomic
traits
Chlorophyll
contents (SPAD value) were recorded with SPAD meter (portable SPAD-502
Chlorophyll Meter (Minolta Co., Ltd.). The leaf area of flag leaf of
mother tiller was measured with
digital leaf area meter (JVC TK-5310). The numbers of tillers of each plant
were manually counted and mean value of five plants was calculated. The plant
height was manually calculated from soil surface to spike tip by scale rod.
The
biological yield of harvested plants (averaged five plants) was measured using electric balance. From each
pot the total numbers of grains per spike of all tillers were counted
manually. Grains yield was determined after threshing the plants.
Plant and soil analysis
Soil sample
from each pot was taken with hand steel auger. For separation of root, pots
were irrigated overnight to make the soil soft and plants were uprooted along
with soil then soil was removed by washing with distilled water. Harvested
plants were further washed with distil water, dried under shade and oven dried
at 110°C for 2–4 h. Plants roots, stems and grains were separately divided and
crushed. The Cd contents in shoots, roots and grains were determined by
following Parkinson and Allen (1975). Briefly, plant sample (0.5 g) was added
di-acids mixture H2SO4–H2O2 and
stay overnight in fume hood. Then, these samples were digested on hotplate
until clear liquor obtained and then filtered and diluted with distilled water.
The prepared samples were analyzed for Cd determination by using atomic
absorption spectrophotometer (Agilent AA-240FS Varian, USA).
Statistical analysis
Experimental data were analyzed using ‘Statistix 8.1’ software. The analysis of variance and
Tukey’s HSD test was applied to check the significance of treatments and
compare the means of treatments at 0.01% probability level, respectively (Steel
et al. 1997).
Results
Analyses of variance showed significant (P ≤ 0.05) effect of all biochar
treatments on all plant and soil studied traits. Soil pH increased with
addition of biochar to polluted soil (Fig. 1–3; Table 1–3) Among the applied biochar types, FYM derived biochar significantly enhanced the soil pH and values increased (7.8–15.7%) with increasing farmyard manure derived biochar
addition to polluted soil as compare to control. The results
highlighted that minimum soil pH was observed in control soil (Fig. 1). The addition
of biochar enhanced the numbers of tillers per plants in polluted soil.
Incorporation of FYM-5 and FYM-10 to polluted soil resulted in greater numbers
of tiller (63.6–77%) in wheat as compared with control soil and the ratio of
tillers was gradually increased with increasing addition of FYM derived biochar
rate. While, the minimum increase in numbers of tillers per plants were noticed
in control soil (Table 2).
Addition of biochar significantly increased the leaf
area in Cd polluted soil as compared to control. Among all applied soil amendments, the maximum increase in leaf
area was observed where farmyard manure derived biochar was applied. The leaf
area increased from 18.7–23.3% for
FYM5-10, and 62.4–79.6% for PS-5 and PS-10, as
compared to control (Table 2). Wheat biomass was relatively increased with
increasing biochar amount from 2.5 to 5 g kg-1 to Cd
polluted soil as compared with control soil. Moreover, the biological yield was
increased with addition of FYM 5–10 from 18.7–21.7%, 26.2–28.8% and 71.3–81.8%
with respect to poultry manure and sugarcane press mud derived biochar and
control soil, respectively. While, minimum biological yield was noticed in
control where no soil amendment was applied (Table 2). Biochar addition
enhanced the grains yield under Cd polluted soil in comparison with control.
The significant increment in grains yield 61.2–77.5% was noted with addition of
FYM derived biochar at 2.5 to 5 g kg-1 to polluted soil with respect
to control soil.
%201633-1640_files/image004.png)
Fig. 1: Effect of biochar
on pH of cadmium contaminated soil after crop harvest
Each value
represents the mean of three replicates ± standard deviation and (P < 0.01)
Control=
Cd-polluted soil; PM-5= Poultry manure biochar 2.5 g
kg-1; PM-10= Poultry manure biochar 5 g kg-1;
FYM-5= Farmyard manure biochar 2.5 g kg-1;
FYM-10= Farmyard manure biochar 5 g kg-1;
PS-5= Sugarcane press mud biochar 2.5 g kg-1;
PS-10= Sugarcane press mud biochar 5 g kg-1
%201633-1640_files/image006.png)
Fig. 2: Effect of biochar
on cadmium (mg kg-1) in contaminated soil after crop harvest
Each value
represents the mean of three replicates ± standard deviation and (P < 0.01)
Control= Cd-polluted soil; PM-5= Poultry manure biochar 2.5 g kg-1; PM-10= Poultry manure biochar 5 g kg-1; FYM-5= Farmyard manure biochar 2.5 g kg-1; FYM-10= Farmyard manure biochar 5 g kg-1; PS-5= Sugarcane press mud biochar 2.5 g kg-1; PS-10= Sugarcane press mud biochar 5 g kg-1
%201633-1640_files/image008.png)
Fig. 3: Effect of biochar on chlorophyll SPAD value of
wheat grown in cadmium contaminated soil after crop harvest
Each value
represents the mean of three replicates ± standard deviation and (P < 0.01)
Control= Cd-polluted soil; PM-5= Poultry manure biochar 2.5 g kg-1; PM-10= Poultry manure biochar 5 g kg-1; FYM-5= Farmyard manure biochar 2.5 g kg-1; FYM-10= Farmyard manure biochar 5 g kg-1; PS-5= Sugarcane press mud biochar 2.5 g kg-1; PS-10= Sugarcane press mud biochar 5 g kg-1
The chlorophyll SPAD value in wheat plants were
considerably increased with addition of press mud, FYM derived biochar and
poultry manure as compared to control (Fig. 3). Among all applied soil
amendments, the addition of FYM 5-10 greatly improved the chlorophyll SPAD
value by 28.8–31.8% as compared with plants grown in control soil; the lowest
chlorophyll SPAD value was measured in control where no soil amendment was
applied.
Cadmium concentration was affected by addition of
poultry manure, FYM derived biochar and press mud to polluted soil and
concentration reduced with increasing the amendment amount. The addition of FYM
derived biochar to polluted soil reduced the Cd in soil (with FYM-5 and FYM-10 by
20.3–63.6 and 64.3–88.1%, respectively) after crop harvest as compared to
control (Fig. 2).
The phytotoxicity of Cd in wheat was decreased with
application of poultry manure, FYM derived biochar and press mud in alkaline
contaminated soil (Table 3). Cadmium was more translocated in roots as followed
by shoots and grains in alkaline polluted soil. Cd was reduced in roots with
addition of biochar to polluted soil, and it was more effective and pronounced
with addition of FYM derived biochar as compared with control and other
treatments. As compared to control, addition of FYM-5 and FYM-10 greatly
reduced Cd toxicities 72.9–90.5%, 91–104% and 83–89% from roots, shoots and
grains of wheat, respectively.
The influence
of biochar on soil N, P and K in Cd polluted soil after wheat harvesting was
also observed (Table 4). The statistical analysis highlighted that addition of
biochar positively influenced the soil N, P and K under Cd toxicity. The maximum nutrient retention was noted with addition
of FYM derived biochar and values
increased for N by 29.6–63.5%, for P by 57.5–72.5% and for K by 45.4–75.5% with
increasing FYM derived biochar amount 2.5 to
5 g kg-1 as compared to
control, respectively (Table 4). The results highlighted that minimum soil N, P and K nutrition
was recorded in control soil where no biochar was applied.
Table 1:
Physiochemical characteristics of experimental soil
|
Parameter |
Unit |
Value |
|
pH |
- |
7.3 |
|
Electrical conductivity |
dS m-1 |
3.7 |
|
Organic matter |
% |
0.67 |
|
Nitrogen |
mg kg-1 |
0.14 |
|
Phosphorous |
mg kg-1 |
7.7 |
|
Potassium |
mg kg-1 |
101 |
|
Sodium |
mmole L-1 |
0.4 |
|
Textural class |
|
Sandy clay loam |
|
Sand |
% |
66 |
|
Silt |
% |
02 |
|
Clay |
% |
32 |
Table 2: Effect of biochar on allometric traits and
yield related parameters of wheat in cadmium contaminated soil
|
Treatments |
Flag leaf area (cm2) |
Number of tillers (pot) |
Plant height (cm) |
Gains yield (g pot-1) |
Biological yield (g pot-1) |
|
Control |
10.03E |
6.06F |
22.6E |
4.9E |
10.2E |
|
PM-5 |
18.0D |
13.9E |
41.1D |
10.03D |
29.0D |
|
PM-10 |
41.2B |
22.0B |
63.0B |
17.2B |
44.2B |
|
FYM-5 |
26.7C |
16.6D |
48.7C |
12.7C |
35.7C |
|
FYM-10 |
49.1A |
27.0A |
74.5A |
21.9A |
56.5A |
|
PS-5 |
21.7D |
11.6E |
35.7D |
8.7D |
26.3D |
|
PS-10 |
37.6B |
19.3C |
54.8C |
14.6C |
40.2BC |
Each value
represents the mean of three replicates ± standard deviation and (P < 0.01)
Control=
Cd-polluted soil; PM-5= Poultry manure biochar 2.5 g
kg-1; PM-10= Poultry manure biochar 5 g kg-1;
FYM-5= Farmyard manure biochar 2.5 g kg-1;
FYM-10= Farmyard manure biochar 5 g kg-1;
PS-5= Sugarcane press mud biochar 2.5 g kg-1;
PS-10= Sugarcane press mud biochar 5 g kg-1
Table 3: Effect of biochar on cadmium (Cd) uptake in
roots, shoots, and grains of wheat in contaminated soil
|
Treatments |
Cd in roots (mg kg-1) |
Cd in shoots (mg kg-1) |
Cd in grains (mg kg-1) |
|
Control |
1.4A |
1.14A |
0.9A |
|
PM-5 |
0.7BC |
0.3B |
0.1B |
|
PM-10 |
0.5BC |
0.2BC |
0.07BC |
|
FYM-5 |
0.4BC |
0.2CB |
0.09CD |
|
FYM-10 |
0.1C |
0.1E |
0.03D |
|
PS-5 |
0.5B |
0.3D |
0.15B |
|
PS-10 |
0.35BC |
0.1CD |
0.09BC |
Each value
represents the mean of three replicates ± standard deviation and (P < 0.01)
Control=
Cd-polluted soil; PM-5= Poultry manure biochar 2.5 g
kg-1; PM-10= Poultry manure biochar 5 g kg-1;
FYM-5= Farmyard manure biochar 2.5 g kg-1;
FYM-10= Farmyard manure biochar 5 g kg-1;
PS-5= Sugarcane press mud biochar 2.5 g kg-1;
PS-10= Sugarcane press mud biochar 5 g kg-1
Table 4: Effect of biochar on soil nitrogen (N), phosphorus (P), and potassium
(K) in cadmium polluted soil after crop harvest
|
Treatments |
Soil N (%) |
Soil P (mg kg-1) |
Soil K (mg kg-1) |
|
Control |
0.01C |
3.1D |
57D |
|
PM-5 |
0.02BC |
5.3CD |
64CD |
|
PM-10 |
0.02B |
7.7BC |
80BC |
|
FYM-5 |
0.02BC |
7.3BC |
81BC |
|
FYM-10 |
0.05A |
11.3A |
156A |
|
PS-5 |
0.02BC |
6.0BCD |
71BCD |
|
PS-10 |
0.036B |
9.3AB |
91B |
Each value
represents the mean of three replicates ± standard deviation and (P < 0.01)
Control= Cd-polluted soil; PM-5= Poultry manure biochar 2.5 g kg-1; PM-10= Poultry manure biochar 5 g kg-1; FYM-5= Farmyard manure biochar 2.5 g kg-1; FYM-10= Farmyard manure biochar 5 g kg-1; PS-5= Sugarcane press mud biochar 2.5 g kg-1; PS-10= Sugarcane press mud biochar 5 g kg-1
Discussion
Addition of biochar (poultry manure,
FYM, and sugarcane press muds) reduced the Cd uptake in wheat by inducing Cd
immobilization in alkaline polluted soil. Soil amendment with various type of
biochar slightly increased soil pH in Cd polluted soil. Farmyard manure derived
biochar caused maximum increase in soil pH in Cd-polluted soil that might be
due to its alkaline nature (Ok et al. 2011; Rizwan et al. 2016b). Alkaline nature of
biochar, containing CaCO3, that dissociate to Ca2+ and CO32−
subsequently the reaction of CO32− with water
liberate OH−1 ions, hence the pH of soil consequently raised
(Ok et al. 2011; Al-Qurainy 2009; Yousaf et al.
2016).
Addition of biochar enhanced the wheat growth and
productivity by altering the organic matter mineralization which is associated
with nutrients retention, especially nitrogen (Sarman
et al. 2018; Olszyk
et al. 2018; Minhas et al. 2020). Addition
of FYM derived biochar improved the numbers of tillers through positive influence on plant growth and
development (Liu et al. 2007). The improvement
might be attributed to positive impact of biochar which improves soil field
capacity, fertilizer use efficiency, nutrients availability from soil to
plants, pH, CEC, and biological properties of soil (Fornazier
et al. 2000) that improve soil health
and nutrients retention, resultantly improving plant growth and increasing the
tillers growth under Cd contamination.
Reduction in plant growth is most common symptom of
heavy metals stress. Various factors for inhibition of plant growth due to
heavy metals stress depends on many physical and chemicals reactions between
heavy metals and soil components (Chang et
al. 2003). Moreover, it reduces the process of nutrient bioavailability and
photosynthesis of plants that affects optimum plant growth and development
under heavy metals toxicities.
The plant leaf area is imperative physiological
parameter to determine plant growth and development. The results indicated that
plant height and leaf area were decreased under Cd stress and these values
improved with addition of FYM derived biochar. Plant height and leaf area
increase might be due to addition of biochar to polluted soil which improved
the nutritional equilibrium by reducing Cd toxicities. The prominent declined
in Cd toxicities might be lowered Cd solubility in pore water or better soil
organic matter capacity to bind with Cd after biochar addition to contaminated
soil (Lu et al. 2017).
Biochar amendment in Cd contaminated soil enhanced the
biological yield and economic yield of wheat. The improvement in wheat yield
was due to better soil properties like soil porosity, microbial activity and
physical properties of soil that provided favorable environment to
microorganism’s (Lehmann and Joseph 2009; Laird et al. 2010). Addition of biochar also provided nitrogen to plants
through ammonia adsorption which improved the plant growth and enhanced the
yield (Thapar et al. 2008; Awad et al. 2017)
as was observed in this study.
In this
study, chlorophyll SPAD value was decreased in Cd polluted soil owing to
changes occurring in leaf anatomy and chloroplast cells structure in the leaf
mesophyll which negatively affect the thylakoid formation in chloroplasts
bundle sheath cells (Anjum et al.
2015). Addition of FYM derived biochar significantly enhanced the chlorophyll
SPAD value. The improvement in chlorophyll SPAD value by addition of FYM
derived biochar was due to more phosphorus, iron, aluminum, and magnesium
contents than other applied biochar (Woldetsadik et al. 2016). Addition of biochar reduced the Cd toxicities in polluted
soil (Younis et al. 2016) by reducing
oxidative stresses and antioxidant enzymatic activities (Nagajyoti
et al. 2010; Gallego et al.
2012). Interaction of heavy metals with cell wall polysaccharides or indirect
disturbance of metabolic processes results in reduced plant growth and
development (Seregin et al. 2004). Mostly, Cd enters into cell membrane and attach with
cell membranes constitutive (phospholipids groups and proteins). The excess of
Cd translocation in plants may create various problems in the functioning of
cell membrane such as exchange and transportation of calcium ions, reduces
plasma membrane H+-ATPase MRNA level (Janicka-Russak
et al. 2008) and substrate of ATPase
is lowered by binding with ATP (Sanz et
al. 2009).
In current study, the Cd concentration
in wheat grains was below the permissible limits (0.2 mg kg−1 dry weight)
(FAO 2012). The possible reduction of metals (below permissible limits) in
plants edible parts (grains, fruits etc.) after addition of soil amendments is
considered as the optimum key additive for safe production (Rizwan et al. 2016a). Many processes
are involved to immobilize the heavy metals by biochar in contaminated soil
such as electrostatic interaction, ion exchange, precipitation, surface
complexation and substitution for Ca by metals during co-precipitation (Uchimiya et al.
2010; Beesley et
al. 2011).
Mostly, Cd was accumulated in plants
roots followed by shoots and grains. Indeed, more Cd accumulation in plants
roots followed by shoots and wheat grains might be due to decreased
translocation of Cd hazards to shoots by localization of Cd toxicities in
plants tissues (Rizwan et al. 2012).
Moreover, the prominent reduction of Cd toxicity in various parts of wheat with
addition of FYM derived biochar might be due to high soil pH that was increased
negatively on charged sites of polluted soil, which resultantly enhanced
cationic metal adsorption (Bradl 2005; Ok et al.
2007).
Nitrogen, phosphorus, and potassium are
important essential macro-nutrients and are required for optimum plant growth
and development. Proper mineral nutrition regulates the adverse environmental
effect on plants and may lower the Cd availability in plants due to nutritional
competition among Cd and essential nutrients (Rizwan et al. 2016a).
Biochar have capacity to retain
macronutrients (Randolph et al. 2017)
that is beneficial for recycling of plant nutrients, reducing nutrient loses by
leaching, and increasing nutrients use efficiency and retention, ultimately
improved soil fertility (Randolph et al.
2017). Biochar addition to soil promoted the nutrients retention that mostly
based on biochar properties such as porosity, surface area, pH and cation
exchange capacity (Yuan et al. 2011;
Farooq et al. 2020b). Biochar
prepared at higher temperature found to be more efficient in promoting
nutrients retention in soil (Hussain et
al. 2017), while biochar pyrolyzed at lower temperature greatly improved
the soil cation exchange capacity (Mukherjee et al. 2011). In acidic soils biochar induced slight change in soil
pH, while minimal decrease in soil pH with addition of biochar was observed in
alkaline soil (Laghari et al. 2015).
Hence, direct and indirect effect of biochar may occur when one assesses the
impact of biochar on nutrient retention supply in soils.
Conclusion
Biochar has showed its potential to induce the
immobilization of Cd in polluted soil and improved the plant growth and
development as compared to non-amended Cd contaminated soil. Among all biochar
amendments, FYM derived biochar (5 g kg-1 of soil) performed better
to remediate Cd toxicity in soil, reduced phytotoxicity in wheat shoots, roots
and grains by improving soil nutrition, which ultimately promoted the wheat
growth and productivity in Cd polluted soil.
Author Contributions
Muhammad Ijaz, Abdul Sattar,
Ahmad Sher – conceptualization, methodology and experiment layout; Muhammad
Ijaz – Supervision; Muhammad Shahid Rizwan, Muhammad Sarfraz– conducted the
experiment and wrote the original draft; Allah Ditta,
Balal Yousaf, Liaqat
Ali – wrote introduction and discussion section; Sami Ul-Allah – review, discussion, editing and proof reading.
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