Effect of biochar on growth and physiology of sugarcane under salinity condition

VIETNAM NATIONAL UNIVERSITY OF AGRICULTURE

FACULTY OF AGRONOMY
---------------------------------------------------

UNDERGRADUATE THESIS
TITLE:
EFFECT OF BIOCHAR ON GROWTH AND
PHYSIOLOGY OF SUGARCANE UNDER
SALINITY CONDITION
Supervisor

: PhD. VU NGOC THANG

Department

: INDUSTRIAL AND MEDICINAL PLANTS

Student

: TRAN THI THUAN

Class

: K61KHCTT

Course

: 2016 - 2021

Major

: CROP SCIENCE

HANOI - 2021


DECLARATION
I hereby declare that this paper is my own work. All results and data in
this thesis are absolutely honest and have not been used in a different thesis. All
sources used in this paper were cited in references.

Hanoi, February 28th ,2021
Student

Tran Thi Thuan

i


ACKNOWLEGEMENTS
To complete this thesis, I am deeply indebted to many people for their
advice, instruction and support.
First and foremost, I would like to send my gratitude to my supervisor,
Dr. Vu Ngoc Thang, Dept. of Industrial and Medicinal plants, Faculty of
Agronomy, Vietnam National University of Agriculture, for his enthusiastic
support, helpful advice and considerable encouragement in the completion of
my thesis.
I would also like to give my gratitude to my teachers who gave me the
necessary knowledge and skills during my time here. Especially I would also
like to give my gratitude to all of my teachers in faculty of Agronomy.

In addition, I would like to acknowledge my family, who always stood
by me, for their in conditional love and support, both financially and
emotionally throughout my work.
Save the best for last, I want to express my thanks to my friends in
Vietnam National University of Agriculture for their friendship and support.
Hanoi, October 12st, 2020
Council secretary

Instructor

Student

Tran Thi Thuan

ii


CONTENTS
DECLARATION.....................................................................................................i
ACKNOWLEGEMENTS...................................................................................... ii
CONTENTS.......................................................................................................... iii
LIST OF TABLES.................................................................................................vi
LIST OF FIGURES..............................................................................................vii
LIST OF ABBREVIATIONS............................................................................. viii
ABSTRACT.......................................................................................................... ix
Chapter I INTRODUCTION.................................................................................1
1.1. Introduction......................................................................................................1
1.2. Objectives and requirements........................................................................... 2
1.2.1. Objectives..................................................................................................... 2
1.2.2. Requirements................................................................................................ 3

Chapter II LITERATURE REVIEW..................................................................... 4
2.1. Situation of sugarcane production on the world and in Vietnam................... 4
2.1.1. Situation of sugarcane production in the world........................................... 4
2.2. Sugarcane production in Vietnam................................................................... 6
2.2. Saline soil and the influence of salinity on the growth and development
of plants........................................................................................................ 8
2.2.1. Saline soil in Vietnam.................................................................................. 9
2.2.2. Effects of saline soils on growth and development of plants and plant
tolerance to saline conditions..................................................................... 10
2.2.3. Some researchs on the effects of salinity on growth, development and
productivity of plant................................................................................... 13
2.3. Applications and research on biochar........................................................... 14
2.3.1. Biochar and properties................................................................................14
2.3.2. The role of biochar..................................................................................... 15
iii


2.3.3. Some research results on biochar............................................................... 16
Chapter III MATERIAL AND METHOD..........................................................18
3.1. Object and Material....................................................................................... 18
3.1.1. Object..........................................................................................................19
3.1.2. Materials..................................................................................................... 19
3.2. Place and time................................................................................................20
3.3. Research contents.......................................................................................... 20
3.4. Methods......................................................................................................... 20
3.4.1. Research methods....................................................................................... 20
3.4.2. Data collection............................................................................................21
CHAPTER 4 RESULTS AND DISCUSSION...................................................24
4.1. Effect biochar on growth parameters of sugarcane under salinity
condition..................................................................................................... 24

4.1.1. Effects of biochar on the plant height of sugarcane under salinity
condition..................................................................................................... 24
4.1.2. Effects of biochar on the plant diameter of sugarcane under salinity
condition..................................................................................................... 26
4.1.3. Effects of biochar on the leaf number of sugarcane under salinity
condition..................................................................................................... 27
4.1.4. Effects of biochar on the leaf length of sugarcane under salinity
condition..................................................................................................... 29
4.1.5. Effects of biochar on the leaf width of sugarcane under salinity
condition..................................................................................................... 31
4.1.6. Effects of biochar on leaf area of sugarcane under salinity condition...... 32
4.1.7. Effects of biochar on the dry weight of stem, leaves, root of sugarcane
under salinity condition.............................................................................. 35
4.1.8. Effects of biochar on the root length of sugarcane under salinity
condition..................................................................................................... 37
iv


4.2. The effect of biochar on the physiology parameters of sugarcane under
salinity condition........................................................................................ 38
4.2.1. Effects of biochar on SPAD index of sugarcane under salinity
condition..................................................................................................... 38
4.2.2 Effects of biochar on chlorophyll fluorescence (Fv/Fm) of sugarcane
under salinity condition.............................................................................. 40
4.2.3. Effect of biochar on water saturation deficit (WSD) in the leaf of
sugarcane under salinity condition.............................................................42
4.2.4. The effect of biochar on the relative ion leakage of sugarcane under
saline condition...........................................................................................44
CHAPTER 5 CONCLUSIONS AND SUGGESTIONS.................................... 47
5.1. Conclusions....................................................................................................47

5.2. Suggestions.................................................................................................... 47
REFERENCES..................................................................................................... 48

v


LIST OF TABLES
Table 2.1: World sugarcane production in recent years........................................ 5
Table 2.2. Sugarcane production in major continents in recent years...................6
Table 2.3. Area, yield and production of sugarcane in Vietnam compared
with the world (2018).............................................................................7
Table 2.4. Sugarcane production by regions in Vietnam, 2017-2018................... 7
Table 4.1. Effects of biochar on leaf area of sugarcane under salinity
condition............................................................................................... 33
Table 4.2. Effects of biochar on the fresh weight of sugarcane under salinity
condition............................................................................................... 34
Table 4.3. Effects of biochar on the dry weight of sugarcane under salinity
condition............................................................................................... 36
Table 4.4. Effects of biochar on the root length of sugarcane under salinity
condition............................................................................................... 37
Table 4.5: Effect of biochar on the relative water content in the leaf of
sugarcane under salinity condition.......................................................42
Table 4.6. Effect of biochar on the relative ion leakage of sugarcane under
salinity condition.................................................................................. 45

vi


LIST OF FIGURES
Figure 1: Sugarcane seedlings before transplanting to pots................................ 19

Figure 2: Wood chip biochar was used in this experiment..................................19
Figure 4.1. Effects of biochar on the plant height of sugarcane under salinity
condition............................................................................................... 25
Figure 4.2. Effects of biochar on the plant diameter of sugarcane under
salinity condition.................................................................................. 26
Figure 4.3. Effects of biochar on the leaves number of sugarcane under
salinity condition.................................................................................. 28
Figure 4.4. Effects of biochar on the leaf length of sugarcane under salinity
condition............................................................................................... 30
Figure 4.5. Effects of biochar on the leaf width of sugarcane under salinity
condition............................................................................................... 31
Figure 4.7. Effects of biochar on SPAD index of sugarcane under salinity
condition............................................................................................... 38
Figure 4.8. Effects of biochar on chlorophyll fluorescence (Fv/Fm) of
sugarcane under salinity condition.......................................................40
Figure 4.9. Effect of biochar on water saturation deficit in the leaf of
sugarcane under salinity condition.......................................................42
Figure 4.10. The effect of biochar on the relative ion leakage of sugarcane
under salinity condition........................................................................44

vii


LIST OF ABBREVIATIONS
ABBREVIATION

MEANING

%

Percentage

ASS

After salinity stress

BSS

Before salinity stress

CV

Coefficient of variation

Et al.

et alii

FAO

Food and Agriculture Organization

FAOSTAT

The Food and Agriculture Organization Corporate
Statistical Database

Fv/Fm

Chlorophyll fluorescence performance indices

ha

Hectare

LSD

Least significant difference

SPAD

Soil Plant Analysis Development

SS

Salinity stress

RWC

Relative water content

viii


ABSTRACT
The individual and combined effects of biochar application dose and
salinity regimes on the growth and physiology of sugarcane. A split-plot
experimental design using and was used. Biochar as a main factor include five
application rates (0, 5 and 10 tons ha-1), while salinity condition as a sub factor
included non-salinity and salinity conditions. Non-salinity condition is achieved

by irrigating with a fully tap water during the growth of sugarcane plants.
Salinity condition was done by irrigating with salinity water at seedling stage (2
months after transplanting to pots). Specifically, plants in each pot were
watering with 200 ml of 100 mM NaCl solution for around 10 days once every
day. Each of 102 plastic pots (260 mm diameter × 210 mm height) was filled
with a old alluvial soils obtained from experimental field at Vietnam National
University of Agriculture, Hanoi, Vietnam. Each pot contained 12 kg of dry soil.
The biochar was applied at 0; 5 and 10 tons biochar/hectare respectively 0; 35
and 70.65 gram biochar/pot before transplanting sugarcane.
The results showed that under effects of stress, sugarcane growth was
inhibited with reductions in plant height, plant diameter, total leaf number, leaf
area, SPAD, partial and total dry weights. Under salinity condition, application
of biochar at 5 and 10 tons ha-1 to the soil increased plant height, plant diameter,
root length, leaf area, the fresh and dry weight, Fv/Fm, the chlorophyll content
while decreased the water saturation deficit in the leaves and the relative ion
leakage. The findings suggest that biochar application at 10 tons ha-1 could be
recommended for ensuring the best growth and physiological parameters of
sugarcane plants.

ix


Chapter I
INTRODUCTION
1.1. Introduction
Salinity is significant abiotic stress that reduces crop productivity, with
the extent of agricultural land salinization increasing due to climate change and
poor land management (Takeda et al., 2008). Salt-affected soils are found in
more than 100 countries and their distribution is extensive and widespread in
arid and semi-arid regions of the world (Saifullah et al., 2018). Salt stress may

lead to decrease in dry matter yield, water and osmotic stress, chlorophyll
content and gas exchange variables (Demiral et al., 2006; Maggio et al., 2007).
Netondo et al. (2004) also reported that photosynthetic activity decreases when
plants are grown under salinity conditions leading to reduced growth and
productivity.
Sugarcane (Saccharum officinarum L.) is a major sugar producing plant.
It is also a high biomass producer and consumes large amounts of water and
nutrients from the soil for achieving maximum productivity. Sugarcane is a
typical glycophyte exhibiting stunted growth or no growth under salinity, with
its yield falling to 50% or even more of its true potential (Subbarao & Shaw,
1985). Many reports have been studied effects of salinity on sugarcane at the
physiological level (Kumar et al. 1994; Wahid et al. 1997; Wahid 2004; Patade
et al. 2008). Errabii et al. (2007) has analyzed effects of salt and mannitol stress
on sugarcane calli in relation to growth, ions, and proline concentrations. Patade
et al. (2008) reported growth reduction in sugarcane calli exposed to lethal salt
concentrations, which might either be due to additive or individualistic effects of
osmotic and toxic components of salinity.
Biochar is the product after any organic material is charred in the presence
of limited O2, by a process called pyrolysis (Abel et al., 2013). Recently, biochar
has attracted consider-able attention as a soil amendment (Saifullah et al., 2018).
1


The direct mechanism of biochar is the enhanced availability of essential
nutrients in the soil, such as K+ and the lessening of Na+ absorption (Chintala et
al., 2014). The indirect mechanism involves the enrichment of soil
physicochemical properties, biological properties, and soil enzymatic activity,
all of which increase the plant water status. Therefore, biochar improved soil
quality and crop productivity in different agricultural soils (Huang et al., 2013).
Xu et al. (2015) found that incorporation of biochar to soils planted with

groundnuts significantly increased yields. Chintala et al., 2014 and Akhtar et al.,
2014 reported that biochar greatly increased the water holding capacity of soil,
physiology characteristics such as chlorophyll content, stomatal conductance,
photosynthetic rate, and relative water content under water deficient conditions.
In addition, some researches were using biochar as a conditioner in salt affected
soils (Elshaikh et al., 2017; Sappor et al., 2017). However, a few researches had
been done to investigate the potential of biochar amendment to enhance fruit
quality by reducing the soil soluble salt under saline water irrigation. For
example, Usman et al. (2016) used biochar under saline water irrigation to
investigate the changes of soil nutrient availability and tomato growth.
Additionally, Lashari et al. (2013) also concluded that biochar amendment
increased the growth, physiology and yield and also increased nutrient uptake of
wheat under salt stress. Therefore, the main objective of the present study was
conducted to investigate effect of biochar on growth, physiology of sugarcane to
inform of biochar’s ability to improve the growth, physiology of sugarcane
under salinity condition.
1.2. Objectives and requirements
1.2.1. Objectives
Research on the effects of biochar on growth and physiology of sugarcane
under salinity condition in the seedling stage in order to to inform of biochar’s
ability to improve the growth, physiology of sugarcane under salinity condition.

2


1.2.2. Requirements
Evaluating the effect of biochar on growth parameters of sugarcane under
salinity condition.
Evaluating the effect of biochar on physiology parameters of sugarcane
under salinity condition.

3


Chapter II
LITERATURE REVIEW
2.1. Situation of sugarcane production on the world and in Vietnam
2.1.1. Situation of sugarcane production in the world
Sugarcane is now the crop with the largest area in the world. Sugarcane is
cultivated in more than 90 countries, mainly in tropical and subtropical areas.
Sugarcane is believed to be one of the oldest industrial crops in the world.
Sugarcane is a major world crop supplying sugar and energy (Henry, 2010).
Along with sugarcane is the sugarcane processing technology and India (Asia) is
the leading country in the world (Nguyen Ngo et al., 1984). From India, China,
the sugar processing industry has spread to Arab, African, European, American
and Australian regions.
Sugarcane belonging to the genus Saccharum, comprises of six species.
There are two confirmed wild species of Saccharum: S. spontaneum and S.
robustum; and four domesticated ones: S. officinarum, S. sinense, S. barberi, S.
edule. Today, all commercial varieties of sugarcane are hybrids derived from
breeding between the species of S. officinarum, and S. spontaneum with
contribution from S. sinense, S. robustum, and S. barberi (Bakker, 1999).
Sugarcane is an important sugar-taken industrial crop in the sugar industry.
Sugar is an important raw material for the food processing industry, the flavor of
everyday meals, and is a provider of energy for the body. Inspite of its long
existed history of 200 years, the sugar industry has recently been mechanized. In
recent years, the sugar industry has grown rapidly. According to the Food and
Agriculture Organization (FAO), nowadays sugarcane is one of the world’s
largest crops by production. Sugarcane is the source of most of the sugar
produced in the world greatly exceeding sugar beet as a source of sugar

(Cordeiro et al. 2007). Currently, sugarcane is cultivated mainly in tropical and
subtropical countries.
4


According to FAOSTAT, by the end of the year 2018, sugarcane has been
cultivated in 104 different countries including: Brazil, India, China, Australia,
Mexico, Indonesia and United States… Brazil is the first country with the largest
area of sugarcane (10 million ha), following by India with about 4.7 million ha,
and China with about 1.4 million ha. Brazil also is the first country with the
highest production of sugarcane (746.8 million-tons) (FAOSTAT, 2018).
Table 2.1: World sugarcane production in recent years
Harvested area

Yield

Production

(million ha)

(ton/ha)

(million ton)

2010

23.69

78.31

1682.84

2011

25.53

77.48

1794.12

2012

26.01

77.60

1831.01

2013

26.86

78.06

1901.87

2014

27.10

76.72

1885.96

2015

26.62

77.65

1875.06

2016

26.60

77.69

1874.61

2017

26.13

78.10

1851.33

2018

26.27

80.02

1907.02

Years

Source: FAOSTAT, 2020
The table 2.1 showed that harvested area, production and yield of
sugarcane in the world have changed significantly. A dramatic in the number of
harvested area of sugarcane was recorded during the years 2010 – 2018, from
23.69 million ha to 26.27 million ha. The number of sugarcane yield increased
dramatically, from 78.31 tons/ha in 2010 to 78.06 tons/ha in 2013 but declined
to 77.69 tons/ha in 2016. From 2018, the sugarcane yield (80.02 tons/ha)
increased dramatically. The production of sugarcane reached to be the highest,
with 1907.02 million ton in 2018.

5


Table 2.2. Sugarcane production in major continents in recent years

Continents

Harvested area

Yield

Production

(million ha)

(tons/ha)

(million tons)

2017

2018

2017

2018

2017

2018

Asia

10.124

10.280

75.706

80.628

695.317

751.902

Europe

0.0379

0.0378

83.483

66.600

2.867

2.280

Americas

13.964

13.920

80.711

80.994

Africa

1.506

1.548

67.663

67.612

92.425

94.925

Oceania

0.497

0.485

84.909

79.867

38.277

35.131

1022.448 1022.786

Source: FAOSTAT, 2020
The table 2.2 indicated that there is a dramatic in the production of
sugarcane from 2017 to 2018. In the 2 years, the sugarcane productions of Asia,

America, Africa have increase tendency recorded at about 56.000 million tons
(in Asia), 338 million tons (in Americas), 500 million tons (in Africa); the
sugarcane productions of Europe & Ocenia decreased nearly 400 million tons
(in Europe), over 3.000 (in Ocenia). Americas has the largest harvested area of
sugarcane with 13.920 million ha in 2018. Although the harvested area declined
44 million ha compared with 2017, the sugarcane yield and production still
increased from 80.711 to 80.994 tons/ha of the yield and from 1022.448 to
1022.786 million tons of the production.
2.2. Sugarcane production in Vietnam
In Vietnam, sugarcane have been grown for a long time in all provinces.
Sugarcane is one of the traditional crops with many purposes: refreshments,
molasses, sugar, fertilizer... and medicine.

6


Table 2.3. Area, yield and production of sugarcane in Vietnam compared
with the world (2018)
Area

Yield

Production

(million hectares)

(tons/ha)

(million tons)

World

26.2698

80.0210

1907.0247

Vietnam

0.2694

73.4176

17.9452

Regions

Source: FAOSTAT (2020)
According to FAO’s forecast, the area, yield, and production of sugarcane
were about 0.269 million hectares; 73.41 tons/ha, 17.9 million tons, respectively
(Table 2.3)
Table 2.4. Sugarcane production by regions in Vietnam, 2017-2018
Harvested
Regions

area
(ha)

Yield

Production

(tons/ha)

(tons)

North & North Central

66,917

59.7

3,993,225

Central Coast – Central Highlands

123,242

60.3

7,433,706

Southeast

25,476

81.1

2,065,535

Mekong River Delta

25,783

75.2

1,938,181

Source: VSSA, FPTS synthesis, 2019
In Vietnam, sugarcane had many advantages over other short-term crops.
In terms of biology, sugarcane is widely adaptable and easy to cultivate, with
good resistance to harsh natural conditions and environments. It also has the
ability to regenerate, helping to reduce production costs. In term of industry,
sugarcane is a multipurpose tree, with possible economic benefits from root to
top. Sugarcane stems can be used for sugar, wine, paper, plywood,
pharmaceutical and electricity production. Regarding natural resources such as
climate and soil, Vietnam is considered as a country with medium potentials for
the growth of sugarcane. In Vietnam, sugarcane was grown in almost regions
7


such as the North and North Central; Central Coast Region and the Central
Highlands; Southeast; and Mekong River Delta (Table 2.4).
2.2. Saline soil and the influence of salinity on the growth and development
of plants
The formation of saline soils is the result of a combination of many
factors: source rock, untrained low-lying terrain, shallow saltwater levels, dry
climate, and salt-loving organisms. Among the elements above groundwater,
salinity is the direct cause of the salty soil. Saline soils are soils that contain

more dissolved salts (1-1.5% or more). Common dissolved salts in soil are:
NaCl, Na2SO4, CaCl2, CaSO4, MgCl2, NaHCO3... These salts have different
origin (continental origin, marine origin, biological origin...), but their original
origin is from volcanic rock mineral elements. During the weathering process of
rock, these dissolved salts move and gather in the form of low drainage without
drainage. In tropical regions with heavy rainfall like Vietnam, the weathering of
rocks occurs strongly, even the insoluble salts such as CaCO3, CaSO4… are
dissolved and washed away into rivers and seas. (Nguyen Thi Thanh Hien, 2016)
Based on the origin and characteristics of salt accumulation, salinity is
divided into two categories: salinity due to the influence of seawater and the
salinity of the continent. The salinization process due to the influence of
seawater is caused by seawater intrusion into the inner field along rivers during
high tide, through storms entering sea dykes or in the dry season when fresh
water flows of rivers. The tower flows into the sea, fresh water is not strong
enough to repel seawater when the tide is strong, salt water can follow the
capillaries of the soil cracks through the sea dykes penetrating deeply into the
interior fields. The process of continental salinity is caused by arid or semi-arid
regions that difficult to dissolve salts remain in the soil, only the soluble salts are
dissolved, but also not transported away to accumulate in the Low-lying terrain
does not drain water in the form of groundwater, due to dry conditions and
8


shallow groundwater levels, salt is moved and concentrated into the surface
layer by evaporation and evaporation. Causes of continental salinization:
capillary water rise from groundwater (the main cause), salt transfer by wind
along with dust from the sea and saltwater lakes, due to salt-washing
precipitation from high terrain. Due to the locking of saline plants in them that
contain a lot of salt, due to irrational irrigation (Tran Van Chinh, 2000)
According to the FAO-UNESCO classification, people rely on the

electrical conductivity of the soil solution and the rate of dissolved salt (%),
saline soils in Vietnam are divided into the following units:
- Salty land of Mangroves (Mn) - Gleyi Salic Fluvisols (FLsg)
- Highly salty soil - Hapli salic Fluviols (FLsh) has total dissolved
salts > 1%, in which Cl- > 0.25% and EC conductivity is usually greater than
4 dS/cm at 25°C
- Medium and low saline soils - Molli Salic Fluvisols (FLsm) have Cl- <
0.25% and EC < 4 mS/cm levels
- Gleyic Solonet
2.2.1. Saline soil in Vietnam
Saline soil in Vietnam covers an area of about 1 million hectares spread
from North to South, accounting for 3% of the country's natural area.
Concentrating mainly in the Mekong Delta, where there are more than 700,000
ha of salty soil, the area is intruded deep in the inner field from 30 - 40 km. In
addition, in the central coastal provinces such as Quang Binh, Ha Tinh, Ninh
Thuan... the area of salty soil is up to several tens of thousands of hectares (Buu
et al., 1995).
According to statistics, more than 50% of the Mekong Delta (39,330 km2)
is salty, including the territories of the provinces: Long An, Tien Giang, Ben Tre,
Tra Vinh, Soc Trang, Bac Lieu, Ca Mau and Kien Giang. On the Vam Co River
from the beginning of the dry season to the beginning of March 2016, the
highest salinity appearing over the same period in 2015 increased from 4.7 - 7.4
9


g/l, specifically on the main river Vam Co at Cau Noi station. The highest
salinity reached 20.3 g/l (February 9, 2016), compared with the same period in
2015 (15.6 g/l) increased by 4.7 g/l. In the area of the estuaries of the Mekong
River, the phenomenon of saline intrusion from the beginning of the dry season
to March 4, 2016, the largest occurrence of salinity compared to the same period

in 2015 increased from 1.5 to 8.2 g/l. At the mouths of Tien and Hau rivers,
salinity also follows the intrusion tide in the river, the intrusion length of salinity
4‰ is about 50 - 57 km (National Department of Science and Technology
Information, February 2016).
The coastal area of Hai Phong is salty about 20,000 ha in both potential
salinity and salinity intrusion from 0.3 to 0.5%. Thai Binh province has about
18,000 ha of saline intrusion. Nam Dinh province has about 10,000 ha. Thanh
Hoa province has about 22,000 ha of salty soil. Along the coast of the central
provinces, the land is also salty, such as Ha Tinh with about 17,919 ha, Quang
Binh with more than 9,300 ha, Ninh Thuan with nearly 2,300 ha, Thua Thien
Hue with about 6,290 ha of land affected by salt. Due to the increasingly serious
situation of saline intrusion, it is necessary to have appropriate measures to
prevent the saline intrusion into the mainland, which greatly affects the
agricultural production of farmers.
2.2.2. Effects of saline soils on growth and development of plants and plant
tolerance to saline conditions
2.2.2.1. Harm of salt to plants
Salinity is one of the most important environmental factors limiting crop
yield because most crops are sensitive to salinity due to the high concentration
of salts in the soil. The immediate consequences of salinity on salt-unsuitable
plants include defoliation, leaf blight, growth retardation, poor seed germination
and plant death (Maas and Hoffman, 1997).
According to Ondrasek et al. (2011) has two main effects of salinity to crops,
including causing physiological drought and inhibition of growth.
10


a. Physiological drought:
The excess salt in the soil increases the osmotic pressure of the soil
solution. Plants obtain water and minerals from the soil when the concentration

of dissolved salts in the soil is less than that of the root cytoplasm, i.e. the
osmotic pressure and water absorption of the roots must be greater than the
osmotic pressure and water absorption of the soil. If the soil salinity rises so
high that the soil's water absorption exceeds the water absorption of the roots,
not only will the plants lose water from the soil, but also lose water into the soil.
Plants do not absorb water, but the evapotranspiration process is still occurring
normally, causing water imbalance, causing physiological drought (Ondrasek et
al., 2011).
Increased osmotic pressure in excessively salty soils is the most important
cause of harm to crops on salty soils.
Salinity affects the physiological activities of the plant:
Water exchange: salinity often hinders the uptake of water by plants and
can cause physiological drought and long-term wilting...
- The synthesis of xytokinin is stopped because the roots are phithormone
synthesizers, so plants lack xytokinin affecting the growth of organs on the
ground.
- The root mineral absorption is inhibited, resulting in a lack of minerals.
Due to the lack of P, the phosphorylation is inhibited and the plant lacks energy.
- The transport and distribution of anabolic in the phloem is inhibited, so
organic matter accumulating in the leaves affects the process of accumulating in
the storage organ...
- The excess of ions in the soil disturbs the membrane permeability, so it
is impossible to check the substances passing through the membrane, leaking
ions out of the roots. Metabolic processes, especially protein metabolism, are
disturbed, leading to the accumulation of amino acids and amides in plants...
(Ondrasek et al., 2011).
11


b. Growth suppression

- The inhibition of plant growth when salty is the most prominent feature.
In saline soils, plants that are less tolerant of salt cease to grow due to inhibited
physiological functions. The higher salt concentration, the stronger the growth
inhibition. Depending on the level of salinity and tolerance that plants reduce
yield more or less (Ondrasek et al., 2011).
2.2.2.2. Plant's resistance to salinity
Regarding the salt tolerance of plants, we must talk about the mechanism
of accumulation and maintaining high concentrations of dissolved substances in
the cells to ensure water competition with salt-contaminated environments and
against drought. The high NaCl content in saline soils makes the plants that
regularly live on this soil have to be able to receive and store Na+, Cl- much
higher than plants that are inherently saline tolerant, and at the same time there
must be changes. Changing physiological activities such as respiration,
photosynthesis, and evaporation of leaves suited the water shortage conditions
of plants.
Many studies have shown that proline plays a key role in protecting cell
membranes, against the harmful effects of high salt concentrations, increasing
cell potential. Proline is a hydrophilic acid in the plant body, synthesized from
glutamine by the stress-inducing enzyme P5CS. Proline is a key constituent of
the quaternary structure of the quaternary amino group and plays an important
role in regulating osmotic pressure of plant cells. Proline concentration in
response to salt stress occurs mainly in the cytoplasm. Therefore, proline
accumulation is considered to be a common adaptive response of higher plants
under drought conditions. Proline is considered as an indicator of drought
tolerance of plants and is also a good indicator of plants that are resistant to salt.
Normally, it is difficult to set a limit on the salinity tolerance of plants, in
general plants die gradually as the salinity increases. However, based on the
average saturated electrical conductivity (Ece) of the soil and the plant response,
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the following salinity levels are recognized: EC is less than 2 mS/cm, does not
affect plants.; EC from 2 - 4 mS/cm, yield of salt-sensitive plants can be reduced;
EC from 4 - 8 mS/cm, yield of many crops may be reduced; ECe from 8-16
mS/cm, only saline tolerant plants produce; EC is greater than 16 mS/cm, there
are only a few salt-tolerant plants for yield.
Unfavorable environmental conditions are one of the most limiting factors
for plant growth, development and productivity. Saline soils are one of the most
important abiotic agents that adversely affect plants due to ion toxicity and
osmotic pressure. In most saline soils, Na+ is one of the cations that are the most
toxic to plant growth, development and productivity. Plants' salinity tolerance is
a complex process that is involved in the biochemistry and physiology as well as
changing the structure and morphology of plants (Zhu, 2001).
2.2.3. Some researchs on the effects of salinity on growth, development and
productivity of plant
Vu Ngoc Thang et al. (2018) shown that increased salt concentration also
decreased root and shoot length of seedlings, fresh weight of roots and shoots
and high NaCl concentration (150 mM) significantly inhibited seeding growth of
both soybean varieties. In potted experiment, plant height, leaf area, dry matter,
nodules, SPAD value, Fv/Fm ratio, yield and yield components decreased with
increasing NaCl concentration, while the water saturation deficit and ion leakage
increased.
The effects of salinity on growth and development are assessed by the
degree of damage at different stages of growth and development. Mass and
Hoffman (1997) also showed that at medium and low salinity can adversely
affect plant growth and development, causing morphological, physiological,
biochemical changes and reduced yield, while high levels of salinity lead to
plant’s death.
According to Kotuby-Amacher et al. (2000) shown that high soil salinity
can also cause nutrient imbalances, result in the accumulation of elements toxic

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to plants, and reduce water infiltration if the level of one salt element-sodium-is
high. In many areas throughout Utah, soil salinity is the factor limiting plant
growth. Salt-affected plants are stunted with dark green leaves which, in some
cases, are thicker and more succulent than normal. In woody species, high soil
salinity may lead to leaf burn and defoliation.
Salt is one of the important abiotic factors affecting plant growth,
physiology and productivity (Taufiq et al., 2016). Salinity affects most stages of
growth and development of the plant and alters the morphology and structure of
the tree (Cakmak, 2005; Nawaz et al., 2010). In particular, high salinity levels
delay the germination process, affecting the germination rate, root length, and
length of germination (Khajeh et al., 2003; Nayer & Reza, 2008; Vu Ngoc
Thang et al., 2017)
2.3. Applications and research on biochar
2.3.1. Biochar and properties
According to IBI (International Biochar Tnitiative), biochar is a solid
obtained from biomass carbonization. Biochar can be added to soil with the aim
of improving soil functions and reducing greenhouse gas emissions. They are of
great significance for carbon fixation according to the cycle of carbon matter in
the atmosphere (Warnock, 2007).
- The physical properties
Biochar consists of 4 main parts: durable carbon, unstable carbon, other
volatile components, mineral ash and moisture. The composition in biochar is
very different depending on the origin of the biomass, the pyrolysis conditions,
the pyrolysis temperature, the rate of heating, the pressure, and the conditions
before and after treatment. The physical properties of biochar depend mainly on
the starting material and the pyrolysis conditions. During pyrolysis, cellulose
and hemium-cellulose at low temperatures are lost in the form of volatile

organic matter, resulting in a loss in mass. The mineral and carbon skeleton
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retains the structural shape of the original material. The molecular structure of
coal is porous and has a large surface area. Very small (50 nm) pores are formed
during pyrolysis that form capillary systems. It is the pore system in coal that is
important for aeration, root zone function and soil structure. Therefore, the
addition of coal to the soil changes the natural physical properties of the soil,
increases the total specific surface area, and improves soil structure and aeration
(Kolb, 2007). In general biochar is usually characterized by a structure of many
dispersed capillaries, made up of holes of different sizes and shapes divided into
3 groups, small, medium and large.
- Chemical properties
In biochar, there is a close combination of elements such as: H, N, O, P, S
in aromatic rings and this causes the electronic affinity of coal, affecting the
exchange ability. The surface charge of coal determines the nature of the
biological interactions between soil particles, dissolved organic matter, gases,
microorganisms and water in the soil. Over time, biochar becomes deactivated
gradually because its pores are sealed and its adsorption capacity will therefore
decrease. The internal voids become inaccessible leading to reduced surface area
(Warnock et al., 2007). Regeneration is possible when bacteria, fungi, and
nematodes settle in those pores of biochar.
- Biological properties
Unlike other types of organic matter added to the soil, biochar changes the
physical and chemical environment of the soil, affecting the properties as well as
the existence and development of soil organisms. The interactions between these
components are crucial to the overall productivity and function of the ecosystem,
such as crop yield and growth.
2.3.2. The role of biochar

- Biochar and soil nutrients
Biochar affects the nutrients available in the soil in two common ways:
nutrient replenishment and nutrient maintenance. The ash in biochar contains
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