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Appraisal for organic amendments and plant growth-promoting rhizobacteria to enhance crop productivity under drought stress: A review

May 2021
Journal of Agronomy and Crop Science 207(5):1-20

May 2021
207(5):1-20

DOI:10.1111/jac.12502

Authors:

Naseer Ullah

Beihang University (BUAA)

Allah Ditta

Shaheed Benazir Bhutto University, Sheringal

Muhammad Imtiaz

Guangzhou University

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Plants are sessile organisms, frequently face unfavourable growth conditions such as drought, salinity, chilling, freezing and high-temperature stresses, inhibiting growth and development, and ultimately reducing crop productivity. Among these stresses, drought stress has been a major challenge for sustainable crop production and a hot area of research under the current climate change scenario. Organic amendments such as biochar (BC) and compost along with plant growth-promoting rhizobacte-ria (PGPR) could be a sustainable strategy to improve crop growth and productivity under drought stress environment. There are several reports about compost, BC, and PGPR application as a single or combined treatment to enhance crop productivity under drought stress. Compost and BC act as conditioners to improve soil physico-chemical and biological properties thereby enhancing water holding capacity (WHC) and nutrient retention and availability to the plants. Both BC and compost also serve as carbon sources and suitable environment for PGPR and endogenous microbes to enhance their growth promotion activities under drought stress. PGPR alleviate drought stress via ACC-deaminase and P-solubilizing activities, production of phyto-hormones, secretion of organic acids, acting as biocontrol agents,etc. In the present review, the individual and combined effect of compost, BC, and PGPR to alleviate drought stress in plants has been critically summarized. Moreover, research gaps and future research directions have been identified and discussed in depth. K E Y W O R D S biochar, compost, drought stress, plant growth-promoting rhizobacteria, rhizobacteria, water deficit

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Appraisal for organic amendments and plant growth-promoting rhizobacteria

to enhance crop productivity under drought stress: A review

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J Agro Crop Sci. 2021;00:1–20. wileyonlinelibrary.com/journal/jac

Received: 18 September 2020

Revised: 9 April 2021

Accepted: 12 April 2021

DOI : 10.1111/jac.125 02

REVIEW ARTICLE

Appraisal for organic amendments and plant growth- promoting

rhizobacteria to enhance crop productivity under drought

stress: A review

Sajid Mehmood7,8 | Muhammad Shahid Rizwan9 | Muhammad Rizwan10

1Environmental Chemistry Laboratory,

Department of Environmental Science

and Engineering, School of Space and

Environment, Beihang University, Beijing,

China

2Department of Environmental Sciences,

Shaheed Benazir Bhutto University

Sheringal, Dir (Upper), Pakistan

3School of Biological Sciences, The

University of Western Australia, Perth, WA,

Australia

4Soil and Environmental Biotechnology

Division, National Institute for

Biotechnology and Genetic Engineering,

Faisalabad, Pakistan

5School of Space and Environment, Beihang

University, Beijing, China

6Department of Biotechnology, Shaheed

Benazir Bhutto University Sheringal, Dir

(Upper), Pakistan

7Guangdong Provincial Key Laboratory

for Radionuclides Pollution Control and

Resources, School of Environmental Science

and Engineering, Guangzhou University,

Guangzhou, China

8School of Civil Engineering, Guangzhou

University, Guangzhou, China

9Cholistan Institute of Deser t Studies,

The Islamia University of Bahawalpur,

Bahawalpur, Pakistan

10Institute of Soil Science, PMAS- Arid

Agriculture University, Rawalpindi, Pakistan

Correspondence

Allah Ditta, Department of Environmental

Sciences, Shaheed Benazir Bhutto University

Sheringal, Dir (Upper) Khyber Pakhtunkhwa,

18000, Pakistan.

Emails: ad_abs@yahoo.com; allah.ditta@

sbbu.edu.pk

Abstract

Plants are sessile organisms, frequently face unfavourable growth conditions such as

drought, salinity, chilling, freezing and high- temperature stresses, inhibiting growth

and development, and ultimately reducing crop productivity. Among these stresses,

drought stress has been a major challenge for sustainable crop production and a hot

area of research under the current climate change scenario. Organic amendments

such as biochar (BC) and compost along with plant growth- promoting rhizobacte-

ria (PGPR) could be a sustainable strategy to improve crop growth and productivity

under drought stress environment. There are several reports about compost, BC, and

PGPR application as a single or combined treatment to enhance crop productivity

under drought stress. Compost and BC act as conditioners to improve soil physico-

chemical and biological properties thereby enhancing water holding capacity (WHC)

and nutrient retention and availability to the plants. Both BC and compost also serve

as carbon sources and suitable environment for PGPR and endogenous microbes

to enhance their growth promotion activities under drought stress. PGPR alleviate

drought stress via ACC- deaminase and P- solubilizing activities, production of phyto-

hormones, secretion of organic acids, acting as biocontrol agents,etc. In the present

review, the individual and combined effect of compost, BC, and PGPR to alleviate

drought stress in plants has been critically summarized. Moreover, research gaps and

future research directions have been identified and discussed in depth.

KEY WORDS

biochar, compost, drought stress, plant growth- promoting rhizobacteria, rhizobacteria, water

deficit

ULLAH et AL.

1 | INTRODUCTION

As the world population is continuously increasing, there is a pros-

pect of global warming due to climate change (Borjas- Ventura

et al., 2020). Besides, the present agricultural activities such as exces-

sive usage of phosphatic fertilizers containing heavy metals, pesti-

cides, herbicides, untreated sewage sludge, industrial effluents, etc.,

are expected to cause pollution and soil degradation (Barrow, 2012).

Thus, food production should be based on environmental sustain-

ability while managing the environmental resources in a way that

evades their further degradation (Godfray et al., 2010). Under field

conditions, plants frequently face unfavourable growth conditions,

for example drought, salinity, chilling, freezing, and high tempera-

tures, which can obstruct plant growth, and in some cases, it could

lead to cause plant death (Chiappero et al., 2019; Zhang et al., 2020).

Under the current climate change scenario, drought stress has been

a significant environmental issue for sustainable crop production

(Delshadi et al., 2017).

Drought is a prolonged dryness period when a region or area

gets a shortage in water supply whether from atmospheric, surface

or groundwater (Mishra & Singh, 2010). It has been a widespread

problem that is 2/3rd of the cultivated area worldwide is facing

drought stress, which is expected to increase in the coming years

due to global warming. Drought stress has deleterious effects on

crop growth and productivity through physiological (stomatal clo-

sure, root architecture, and so on) and biochemical changes (oxi-

dative stress) and ultimately poses a threat to food security (Aslam

et al., 2013; Carvalho et al., 2021). It is highly likely to investigate

certain amendments with the potential to enhance crop productivity

under drought stress and ultimately leading to food security.

Rhizobacteria are found in the rhizosphere of plants and those

having beneficial effects directly or indirectly on plant growth

and productivity through various mechanisms are termed as plant

growth- promoting rhizobacteria (PGPR) (Danish et al., 2020; Kasim

et al., 2013; Saharan & Nehra, 2011). The utilization of PGPR has

been an attractive and sustainable strategy for increasing crop

production under drought stress by replacing chemical fertiliz-

ers and pesticides (Kaushal & Wani, 2016). Various genera of rhi-

zobacteria like Pseudomonas, Azospirillum, Azotobacter, Klebsiella,

Enterobacter, Alcaligenes, Arthrobacter, Burkholderia, Bacillus and

Serratia have been investigated to improve the growth and produc-

tivity of various plants under drought stress (Danish & Zafar- Ul-

Hye, 2019; Kanwal et al., 2017; Kazeminasab et al., 2016; Mishra

& Singh, 2010; Zafar- ul- Hye et al., 2019). These drought- tolerant

PGPR induce systemic resistance in plants against drought (Hussain

et al., 2014; Kasim et al., 2013; Naveed et al., 2014). Under abiotic

stresses such as drought, there is an increased ethylene production,

which has a deleterious effect on the plants’ root growth (Arshad &

Frankenberger, 2002). Ethylene at low concentration (<25 µg/L) has

a stimulatory effect on crop growth while its higher concentration

inhibits seed germination and root development (Abeles et al., 1992;

Shaharoona et al., 2006). There are certain drought- tolerant PGPR

(Pseudomonas fluorescens, Pseudomonas fluorescens biotype G,

Pseudomonas putida biotype A, Burkholderia caryophylli, and so on)

that have ACC- deaminase activity which helps reducing ethylene

stress on roots (Shaharoona et al., 2006, 2007). The enzyme ACC-

deaminase converts 1- aminocyclopropane- 1- carboxylic acid (ACC), a

precursor of ethylene into ammonia and α- ketobutyrate through de-

amination (Shaharoona et al., 2006). In this way, PGPR improve root

architecture, which ultimately enhances plant water uptake under

drought stress (Nadeem et al., 2017). Other mechanisms through

which PGPR enhance crop growth and productivity under drought

stress include biological nitrogen fixation (BNF) through a symbi-

otic association between Rhizobia and plants, production of various

phytohormones (gibberellic acid, auxins, cytokinins, and so on), etc.,

(Ahmad et al., 2021; Kasim et al., 2013; Saharan & Nehra, 2011).

Biochar (BC) is carbon- rich organic materials derived through

the pyrolysis of agricultural wastes under minimal/no oxygen supply

(Bitarafan et al., 2020; Rizwan et al., 2018). BC can retain carbon

in soil and lessens the negative impacts of drought stress on crop

growth (Akhtar et al., 2014). Presently, BC is grabbing considerable

attention around the globe as a mean for carbon sequestration

and to decrease surface and groundwater contamination (Abbas

et al., 2018; Abideen, Koyro, Huchzermeyer, Ansari, et al., 2020;

Abideen, et al., 2020; Adejumo et al., 2020; Barrow, 2012; Bashan

et al., 2012). The characteristic of BC may moderate the effects

of drought on crop yield in areas, prone to drought stress. BC is a

beneficial soil amendment in retaining soil moisture, especially

under drought stress. It is an easily available input for sustain-

able agriculture and reduces global warming and land degradation

(Barrow, 2012). Poultry manure- derived BC serves as a natural or-

ganic fertilizer due to the large amount of NPK, and other micronu-

trients. Under drought stress, it improves the WHC of the soil due to

its positive effect on soil physicochemical and biological properties

(Bashan et al., 2012; Murtaza et al., 2021). Similarly, BC application

to sandy soil is beneficial to both crop growth and dramatically im-

proves the P availability of the coarse soil (Bashir et al., 2020; Foster

et al., 2016).

The use of BC is suggested for crops as it improves the mois-

ture contents of the soil (Abideen, Koyro, Huchzermeyer, Bilquees,

et al., 2020; Bitarafan et al., 2020; Rittl et al., 2018). When BC is

applied, it improves WHC and soil fertility by increasing soil organic

matter by a factor of 10– 100 and minimizes greenhouse gases emis-

sion from soils due to its stable nature against microbial decomposi-

tion (Cheng et al., 2008; Hale et al., 2011; Rittl et al., 2018; Roberts

et al., 2010). BC can make renewable energy in a climate- friendly

way and acts as an essential amendment for the soil to increase crop

productivity (Barrow, 2012). Due to its slow degradation in the soil,

it acts as a carbon source for soil microorganisms. As clear from

Figure 1, the high surface area and porous structure of BC provide a

safe environment for the soil microorganisms against various biotic

and abiotic stresses (Chen et al., 2014; Hale et al., 2014).

Compost is organic matter that has been decomposed through

compos ting. The application of compost improves the physicochem-

ical and biological properties of the soil (Ahmad et al., 2017; Salehi

et al., 2016), increases its WHC, which ultimately improves plant

ULLA H et AL.

growth and productivity under drought stress (Shahzad et al., 2014).

The addition of compost to the soil not only improves the soil or-

ganic matter but also increases the amount of available macro- and

micro- nutrients for crop growth (Ditta, Imtiaz, et al., 2018; Ditta,

Muhammad, et al., 2018; Singh, Singh, et al., 2019; Somerville

et al., 2019). Regarding the biological properties of soil, organic

amendments improve the microbial activities and their diversity in

soil, thereby improving nutrient release for crop growth and produc-

tivity (Singh, Prabha, et al., 2019).

Residues of agricultural wastes such as straws, nutshells, fruit

peels, fruit seeds, stoves and green leaves are among the pri-

mary raw materials for the production of BC and compost (Ditta,

Muhammad, et al., 2018; Singh, Prabha, et al., 2019). The disposal

methods currently being used to manage these residues are a source

of extensive environmental pollution. For example, disposal of rice

an d wheat st raw by open- f iel d burn ing cau s es air pollu tion. In th is re-

gard, organic amendments and PGPR could be a sustainable strategy

to improve crop growth and productivity under normal and drought

stress conditions. There are many reports about the combined syn-

ergistic effect of compost and BC (Adejumo et al., 2020; Bashir

et al., 2020; Obadi et al., 2020; Ramzani et al., 2017; Somerville

et al., 2019), compost, and PGPR (Armada et al., 2014; Duo

et al., 2018; Kanwal et al., 2017; Kazeminasab et al., 2016; Shahzad

et al., 2014; Yaseen et al., 2019), BC and PGPR (Ullah et al., 2020;

Zafar- ul- Hye et al., 2019) and compost, BC and PGPR (Nadeem

et al., 2017) under drought stress. The unique mechanisms respon-

sible for plant growth promotion have been discussed in earlier sec-

tions (Figures 2– 4). More specifically, organic amendments such as

BC and compost act as a conditioner to enhance soil physicochem-

ical properties, a nutrient source for plants, and a carbon source,

and a suitable environment for PGPR and indigenous microbes to

enhance their growth promotion activities under drought stress. In

the present review, first we have described the impacts of drought

stress from growth, physiological, and biochemical point of view.

We have then critically summarized the role of the individual and

combined application of organic amendments and PGPR to alleviate

drought stress through various mechanisms in plants. Moreover, the

research gaps found and future research directions for further stud-

ies have been proposed.

2 | IMPACT OF DROUGHT STRESS ON

PLANTS

Drought is a meteorological term and it takes place when there is a

subs tantial loss of moisture from the surfa ce of the soi l to the at mos-

phere. It may also arise due to less water supply through rainfall or

any other source of precipitation to soil (Aslam et al., 2013). Drought

is a severe threat to food security having deleterious effects on the

growth, physiological, and biochemical processes of plants (Farooq

et al., 2020; Van der Weijde et al., 2017). It affects plant- water re-

lations on both the cellular and whole plant levels, which leads to

various specific and non- specific phenotypic and physiological re-

sponses (Beck et al., 2007). During drought stress, water availability

and turgidity of crops are decreased which disrupts the normal func-

tioning of the plant body (Sinha et al., 2016, 2019). Drought stress

has detrimental effects on the establishments of crop seedlings,

leaves and root growth, photosynthesis, pollination, grain develop-

ment, and ultimately on crop productivity (Farooq et al., 2017; Jaleel

et al., 20 09). The effect of drought stress is apparent at every step

of plant development and varies from morphological to molecular

stages. Drought stress significantly reduces seed germination and

FIGURE 1 The high surface area (a) and pore structure (b) of

biochar provide a safe environment for the soil microorganisms,

which enhance soil microbial activities and ultimately nutrient

availability to the crop plants under drought stress (Chen

et al., 2014; Hale et al., 2014)

(a)

(b)

ULLAH et AL.

seedling development (Chiappero et al., 2019). Drought inhibits

leaf expansion and stomatal development resulting in lower photo-

synthesis, which finally reduces plant biomass (Endres et al., 2019;

Keipp et al., 2020) via oxidative stress (Aslam et al., 2013; Bistgani

et al., 2017; Elsayed et al., 2019). Several processes such as hydrau-

lic status, osmotic adjustment, phytohormones, and reactive oxy-

gen species (ROS) signals reduce plant growth under drought stress

(Guangyu et al., 2020; Moreno- Galván et al., 2020). ROS are the

by- products of aerobic metabolism, which are produced in various

cellular organelles such as chloroplasts, mitochondria, and peroxi-

somes under abiotic stress conditions. As reactive molecules, ROS

oxidize and modify cellular components, thereby causing irreversible

DNA damage and even cell death (Huang et al., 2019). Physiological

characteristics of plants such as gaseous exchange and water use

efficiency are mainly disturbed under drought (Carvalho et al., 2021;

Cotrim et al., 2020; Goodarzian- Ghahfarokhi et al., 2016). Moreover,

the integrity of cellular membranes, photosynthetic pigments, os-

motic adjustment of osmolytes, and photosynthesis are severely

affected by drought stress (Jafari et al., 2019). Both stomatal con-

ductance and leaf expansion are key mechanisms in plants to sur-

vive under drought stress conditions (Romdhane et al., 2019; Talbi

et al., 2020; Zlobin et al., 2018).

When plants are exposed to drought stress, there is a significant

reduction in leaf water potential, relative water contents, and tran-

spiration rate with an abrupt increase in leaf temperature (Bistgani

et al., 2017). The soil- plant- atmosphere greatly determines the

transpiration rate of crops. According to Salehi et al. (2016), water

deficiency alters the osmotic potential of tissue, defences against ox-

idative stress and growth rate. However, the growth of plant species

is differently affected by drought stress. Reduction in leaf size allows

plants to respond against water shortage (Jin et al., 2015). Stomatal

closure in plants is the first line of defines against drought stress,

which reduces the exchange of water, carbon dioxide, and oxygen

and ultimately reduces photosynthetic rate (Hlaváčová et al., 2018;

Kanwal et al., 2017; Kasim et al., 2013). Photosynthesis is the main

feature limited in plants exposed to drought stress, mostly under

arid and semi- arid climatic conditions (Talbi et al., 2020).

3 | IMPACT OF ORGANIC AMENDMENTS

AND PGPR ON CROP PRODUCTIVITY

UNDER DROUGHT STRESS

3.1 | Biochar

The use of biochar (BC) is gathering attention as a carbon- rich or-

ganic amendment for agriculture and environmental sustainability

(Bitarafan et al., 2020; Yang et al., 2020). The potential benefits of

the BC have readily been observed under limited water conditions

(Table 1). Adejumo et al. (2020) stated that BC has prospective ef-

fects on the production of agricultural products and remediation of

soil and water under stress due to its role in improving plant growth

and diminishing heavy metals’ pollution (Ijaz et al., 2020; Rizwan

et al., 2021). Various researchers have reported enhanced crop yield

FIGURE 2 Effects of biochar on

different characteristics of soil under

drought stress (Chen et al., 2014; Hale

et al., 2014)

ULLA H et AL.

following BC application to fertilizer amended soil that was infertile

and under drought stress (Abideen, Koyro, Huchzermeyer, Ansari,

et al., 2020; Abideen, Koyro, Huchzermeyer, Bilquees, et al., 2020;

Ahmed et al., 2018; Deluca et al., 2015). The increase in crop growth

and yield is commonly observed with the application of BC to soils

yet experimental outcomes are dynamic and depend on the experi-

mental set- up and soil properties.

The high surface area and porous structure of BC provide a safe

environment for microorganisms in the soil, which increases the

availability of micro- and macro- nutrients for plants under drought

stress (Figure 1). Moreover, BC improves soil porosity, moisture re-

tention capacity, and water use efficiency to reduce drought effects

on crop yield (Abideen, Koyro, Huchzermeyer, Ansari, et al., 2020;

Hafeez et al., 2017; Hansen et al., 2016). Since BC has high organic

carbon contents, it can act as a soil conditioner to improve the phys-

icochemical and biological properties of soil (Murtaza et al., 2021).

Increased plant growth such as in tomato (Akhtar et al., 2014;

Mulcahy et al., 2013) and barley (Hansen et al., 2016) has been

observed under drought stress via BC application. BC enhanced

drought stress tolerance under reduced irrigations in tomatoes

(Akhtar et al., 2014).

Although many studies have reported the efficacy of biochar ap-

plication in the soil for optimum growth and productivity of plants,

there are also some limitations. For example, the adsorption poten-

tial of biochar for plants nutrients especially N and Fe may result in

their deficiency (Kim et al., 2015). The positive effects of biochar

are dependent on pyrolysis temperature, biochar aging, soil type,

plant species, etc. (Kavitha et al., 2018). Biochar produced at high

temperatures tends to have more pH and it may not be suitable for

alkaline soils due to the formation of P precipitates with Ca and Mg,

thereby causing phosphorus deficiency (Xu et al., 2016). There are

also reports about the magnification of contaminants through bio-

mass used for biochar preparation (Jones & Quilliam, 2014). The

aged biochars may also have a detrimental effect on the growth of

earthworms and/or fungi (Anyanwu et al., 2018), thereby affect-

ing soil health and nutrient availability. Despite the above, a recent

meta- analysis study reported that application of biochar @ >50 t/ha

would be required for improvement of hydraulic properties of sandy

soils under laboratory conditions (Rabbi et al., 2021). The authors

suggested that the application of such a huge amount would involve

high costs during biochar production and would require further re-

search I producing effective biochar with optimum porosity, surface

area, and hydrophilic properties.

3.2 | Biochar and compost

Recently, the integration of organic amendments is gaining interest

to improve soil fertility and crop productivity under drought stress

(Akhtar et al., 2014). The combined use of biochar (BC) and compost

has a synergistic effect on crop growth and productivity, especially

under drought stress (Table 2). An increase in soil WHC, plant water

status and plant ions, net photosynthesis, and photosystem II effi-

ciency in Phragmite s karka after BC ap plication was observed (Abideen,

FIGURE 3 Effects of compost on

different characteristics of soil under

drought stress (Bashir et al., 2020;

Ramzani et al., 2017)

ULLAH et AL.

Koyro, Huchzermeyer, Bilquees, et al., 2020). Moreover, plants treated

with BC had lower oxidative stress, enhanced water- use proficiency,

and diminished soil respiration. The BC- compost blend considerably

improved the plant growth, leaf turgor potential, and gaseous ex-

change parameters such as photosynthesis, transpiration, etc.

Obadi et al. (2020) conducted a study on sweet pepper (Capsicum

annum L.) to evaluate the effect of BC and compost under partial root-

zone dr ying ir rigat ion (droug ht st ress). In resul t s, a su bstantia l decl ine in

morphological traits like flowering, fruit set, and vigorous fruit- bearing

stages due to a reduction in the water supply was observed. A strong

beneficial outcome on plant development such as plant height, num-

ber of leaves, and yield was observed with the combined application

of BC and compost at the rate of 2% (w/w). It was suggested that the

combined utilization of BC and compost with partial root- zone drying

irrigation strategy (80% ETc) could be a practical manage me nt strategy

to improve the production of sweet pepper by saving about 22% of

applied water. Adejumo et al. (2020) studied the growth of maize in

lead- contaminated soil under drought stress and found that compared

to un- amended soil, the combination of BC with compost enhanced

biomass production in stressed maize crop by 50%– 75%. Similarly,

Bashir et al. (20 20) demonst rated that Cd and drought alone decreased

the wheat growth, elevated the oxidative stress and Cd contents in

wheat tissues while application of co- composted farm manure and BC

increased the growth, yield, chlorophyll contents and minimized the

oxidative stress in the leaves along with the reduction in Cd concentra-

tions in wheat tissues mainly in grains.

Ramzani et al. (2017) studied the application of acidified BC and

compost in three soils having different stresses to examine the qui-

noa growth, physiological response, and seed nutritional quality. It

was found that drought, salt- affected and nickel- contaminated soils

produced ROS in quinoa plants, which were reduced by the addition

of acidified BC and compost. Moreover, plant growth, yield, physio-

logical, chemical, and biochemical parameters were significantly im-

proved under all stressed soils by applying acidified BC and compost.

Nevertheless, when combined with compost, the results of BC ap-

plications have not been completely grasped and need further eluci-

dation, especially under long- term field trials. Also, BC and compost

combined response has not been studied extensively in vegetables,

especially under sandy soil conditions, and require further research

in the future with a special focus on the response mechanisms of soil

properties (carbon sequestration) to biochar application under long

term field conditions.

3.3 | Biochar and PGPR under drought stress

The function of PGPR in the establishment , grow th, and drought tol-

erance in plants is the product of the sum of nutritional, physiological,

FIGURE 4 Effects of PGPR on

different characteristics of soil under

drought stress (Barnawal et al., 2017;

Govindasamy et al., 2020; Saharan &

Nehra, 2011)

ULLA H et AL.

TABLE 1 Impact of biochar on plant growth under drought stress

Feedstock

Pyrolysis

Temp.

Application

rate Drought condition Crop plant Impact Reference

Corn straw 500°C 5% Full irrigation (30% of soil volumetric

water content), deficit irrigation (soil

moisture decreased to 10%) and

alternate root- zone drying irrigation

Quinoa

(Chenopodium

quinoa)

Biochar improved both photosynthesis

and stomatal conductance in all irrigation

regimes, enhanced plant height, shoot

biomass, and grain yield by 11.7%, 18.8%

and 10.2%, respectively

Yang

et al. (2020)

Rice husk, standard rice husk,

wheat straw or oilseed rape

straw

500°C 2% Irrigation was reduced from 80% of FC

to 40% in half of the pots to create

water stress when 50% of the plants

flowered

Fenugreek

(Trigonella foenum-

graecum L.)

All standard biochars increased plant dry

weight (18% − 25%) and number of seeds

pod−1 (9.0% − 14.5%) compared with the

control

Bitarafan

et al. (2020)

wheat straw 55 0°C 0, 5, and 10 g/

Drought stress (main factor): soil

moisture was kept at 75%– 80% WHC

as control (D- C), 40%– 45% WHC as

low drought stress (D- L), 20%– 25%

WHC as high drought stress (D

Soybean(Glycine

max)

Biochar addition significantly enhanced

soybean grain yield by 3.1%– 14.8%,

Zhang

et al. (2020)

Coniferous wood and hardwood

chips (1:4 ratio by weight)

750° C 0%, 0.75% and

2.5%

The WHC was kept at 40% of maximum

WHC of the respective treatment.

Tall Reed

(Phragmites karka)

Biochar application enhanced plant fresh

and dry biomass, root to shoot ratio and

root mass fraction, was paralleled by

an increase of chlorophyll content, net

photosynthesis rate and WUE of plants

and reduced oxidative stress

Abideen, Koyro,

Huchzermeyer,

Ansari,

et al. (2020)

Poplar (Popolus alba L.) woodchip 800°C 0% and 1%

(w/w), 2.6 kg

BC m−2

Natural rainfall without irrigation Maize (Zea mays)Biochar improved physicochemical

characteristics and the water content

of treated soils with increased root

elongation and transpiration

Romdhane

et al. (2019)

Rice straw 450 and

550° C

0%, 3.0% and

5.0%

Three levels of drought stress (well-

watered, mild drought and severe

drought containing 70%, 50%, and

35% of soil WHC respectively) were

applied to 45- d- old wheat plants

Wheat (Tr iticu m

aestivum)

Biochar improved morphological and

physiological parameters of wheat

under combined drought and Cd stress

and reduced the oxidative stress and

Cd contents and increased antioxidant

enzymes activities

Abbas

et al. (2018)

Rice straw 450 and

550° C

0%, 3%, and

5%, (w/w)

Three moisture levels including zero

drought as a control (1– 2 cm water

layer on soil), mild drought (MD, 50%

of soil WHC), and severe drought (SD,

35% of soil WHC)

Rice (Oryza sativa) The biochar supply reduced the

bioavailable Cd in the soil whereas

increased the soil EC and pH than the

control treatment.

Rizwan

et al. (2018)

Wheat straw 350– 550°C 0, 25 and 50 t/

Three irrigation regimes (W1 = 50%,

W2 = 75% and W3 = 100% of the

reference evapotranspiration)

Tom ato (Solanum

lycopersicum)

The integration of BA along with DI can

be considered as a viable approach that

improves crop productivity and promotes

irrigation water use efficiency

Agbna

et al. (2017)

(Continues)

ULLAH et AL.

Feedstock

Pyrolysis

Temp.

Application

rate Drought condition Crop plant Impact Reference

Corn cob 450°C 10, 20 t/ha For water level treatments pots were

watered after two days and pots with

non stress conditions were watered

daily

Soybean (Glycine

max L.)

Biochar significantly improved sugar and

proline content under drought stress as

compared to control

Hafeez

et al. (2017)

Wood chip sieving of Picea abies

L. (70%) and Fagus sylvatica L.

(30%)

550– 6 00 °C 0, 15 and

30 Mg/ha

Watering regime (rainfed or irrigated) Maize(Zea mays),

wheat (Tr iticu m

aestivum), peas

(Pisum sativum)

and barley

(Hordeum vulgare)

Biochar amendments significantly reduced

NO3 leaching, improved soil moisture and

higher NO3 amount

Haider et al.

(2017 )

Rice husk and shell of cotton

seed

400°C 0% and 5%

(w/w)

Three irrigation regimes, i.e. full

irrigation (FI), deficit Irrigation (DI),

and partial root- zone drying irrigation

(PRD). In case of FI, plants were

irrigated daily to FC while in DI and

PRD, 70% water used for FI was

irrigated on either the whole or one

side of the pots, respectively

Tomato (Solanum

lycopersicum)

Biochar increased the soil moisture

contents in DI and PRD, which

consequently improved physiology, yield,

and quality of tomato as compared with

the non- biochar control. Also, water use

efficiency, leaf relative water content,

membrane stability index and fruit yield

were improved

Akhtar

et al. (2014)

Pseudotsuga menziesii - 0%, 15% and

30% (v/v)

Plants were watered daily, and

abundantly, for the first 24 days after

transplanting, but not thereafter

Tomato (Solanum

lycopersicum)

Biochar application (30% v/v), significantly

increased seedling resistance to wilting

Mulcahy

et al. (2013)

TABLE 1 (Continued)

ULLA H et AL.

TABLE 2 Impact of biochar and compost on plant growth under drought

Plant spe cie Biochar Compost Drought Stress Impact References

Wheat ( Tritic um

aestivum)

Garden peat Farm yard manure Seeds were sown in the soil at normal soil moisture (70%

of soil WHC level. Both normal and drought stress (35%

WHC) levels, after 50- day of sowing, were applied and

plants were harvested at 122 days after seed sowing

Shoot dry weight increased by 80% and 95%

while dry root weight increased by 68%

and 82% and spike length and grain weight

increased by 69% and 87% under normal and

drought stress

Bashir

et al. (2020)

Sweet pepper (Capsicum

annuum L.)

Date palm Commercial Compost Partial root zone drying irrigation (PRD) i- e IR1 (80%

ETc) and IR2 (100% ETc).

Moderate improvement (39.9%) in yield with a

higher WUE (103.8%) than the control

Obadi

et al. (2020)

Maize (Zea mays) Rice husk Mexican sunflower and

poultry manure

Drought stress was imposed by reducing the soil FC to

25% and 50%.

Biochar in combination with compost

enhanced biomass production in stressed

maize crop by 50%– 75% compared to

unamended soil

Adejumo

et al. (2020)

Mesic (Corymbia

maculate) and Xeric

(Eucalyptus torquata)

tree

Eucalypt hardwood Municipal green waste All WD pots received 50% of the estimated daily mean

evapotranspiration (ET) measured for the WW pots of

the same species

The ET of the xeric tree species was greater

for all the OM amended soils for both well-

watered (WW) and water deficit ( WD) plants.

The compost/biochar amended clay soil had

PAW that was 69% of the control PAW

Somerville

et al. (2019)

Wheat ( Tritic um

aestivum)

Rice husk ash Farm yard manure The control and traditional packages received full

irrigation water whereas emergent agronomic package

received ~10% less irrigation water for observing the

crop performance under reduced water application

Irrigation (WPi) and total water productivity

(WPt) were respectively found maximum

under reduced (0.67 ± 0.01 and

0.57 ± 0.01 kg/ha mm) and full irrigation

with organic amendments (0.66 ± 0.03 and

0.57 ± 0.02 kg/ha mm) whereas minimum

under RB (0.53 ± 0.01 and 0.46 ± 0.01 kg/

ha mm) and control with full irrigation

(0.54 ± 0.01 and 0.46 ± 0.01 kg/ha mm)

Singh, Singh,

et al. (2019)

Quinoa

(Chenopodium quinoa

Willd.)

Maize cob Maize plants Drought- stressed soil was artificially created by the

reduction of 80%– 85% crop water requirement

Acidified biochar increased root, shoot, seed

yield pot−1, A, E, gs and chlorophyll content

by 61%, 60%, 55%, 33%, 81%, 51% and 70%

in salt- affected; 31%, 50%, 38%, 31%, 41%,

42% and 61% in Ni contaminated and 58%,

62%, 62%, 43%, 100%, 79% and 88% in

drought soil, respectively, compared to their

corresponding controls

Ramzani

et al. (2017)

Maize (Zea mays) Virgin pine wood Steer

manure

Irrigation occurred once per week for the well- watered

“full” irrigation and all irrigation inputs were withheld

from the appearance of the seventh collared leaf (V7)

to maize tasseling for limited irrigation treatment.

In comparison to the control, manure

application increased gravimetric soil

moisture by approximately 15%, total

nitrogen by 10%, usable phosphorus by

45% and microbial biomass carbon by 15%

(p <.05). Relative to power, biochar raised

overall soil carbon by 80 percent and

changed EEAs (p <.05).

Foster

et al. (2016)

ULLAH et AL.

and cellular effects of PGPR on plants (Czarnes et al., 2020). PGPR

control the physiology of plants to a superior degree due to their

large number in the rhizosphere (Kasim et al., 2013). The combined

application of PGPR with BC has various additional benefits for ex-

ample, the BC not only improves the physicochemical properties

of the soil but also serves as carrier material for PGPR inoculation

(Danish et al., 2020; Ullah et al., 2020). BC as carrier material for

PGPR not only serves as a carbon source for bacterial multiplica-

tion but also provides a safer environment against various biological

competitors in soil due to porous structure (Chen et al., 2014; Hale

et al., 2014). Moreover, the combined application reduces the costs

involved during the separate application of PGPR and BC.

The combined effect of BC with PGPR or inoculated BC has been

summarized in Table 3. Various researchers have confirmed the role

of BC and PGPR in improving crop growth and productivity under

drought stress via an increase in organic carbon and WHC of the soil,

carbon source for PGPR, provision of protection sites for microbes,

and subsequent microbial action against ethylene stress and various

other mechanisms (Danish & Zafar- ul- Hye, 2019; Danish et al., 2020;

Ullah et al., 2020; Zafar- ul- Hye et al., 2019). Although biochar with

PGPR has a positive effect on crop productivity; further research

is needed to confirm its efficacy under long- term field conditions

under various climatic conditions.

3.4 | Compost and PGPR under drought stress

The combined application of compost and PGPR has a synergis-

tic effect on crop growth and productivity under drought stress.

The compost adds organic carbon to the soil, thereby improving

soil physicochemical and biological properties of the soil (Bashan

et al., 2012). The compost is also well renowned for the provision

of micro and macronutrients to the plants (Ditta et al., 2015; Ditta,

Imtiaz, et al., 2018; Ditta, Muhammad, et al., 2018). Combined with

PGPR, compost serves as carrier material for microbial inoculation

of crop seeds, thereby improving their survival and subsequent mi-

crobial activities for example, enhanced ACC- deaminase activity to

scavenge ethylene stress, P- solubilizing activity to enhance phos-

phorus availability, production of phytohormones, exopolysaccha-

rid es, organic acids, etc. (A hmad et al., 2017; Duo et al., 2018; Moridi

et al., 2019; Yaseen et al., 2019, 2020). As summarized in Table 4,

various researchers have confirmed a synergistic effect of compost

with PGPR on crop growth and productivity under drought stress.

For example, seed inoculation with PGPR (Alcaligenes faecalis,

Bacillus amyloliquefaciens, and Pseudomonas moraviensis) along with

the application of biogas slurry (BGS) under drought stress condi-

tions showed significantly improved grain and biological yield of

wheat (Yaseen et al., 2019). Further, the combined application of

PGPR with BGS was suggested as a sustainable strategy for im-

proved crop growth and productivity under drought stress. Earlier,

the combined application of compost with rhizobacteria enhanced

crop growth, quality, and productivity under desertified soil con-

ditions (Ahmad et al., 2017; Duo et al., 2018; Kanwal et al., 2017;

Moridi et al., 2019; Yaseen et al., 2019, 2020). Under semiarid con-

ditions, the application of indigenous microbes with Aspergillus niger

treated agro- wastes alleviated drought stress and subsequently en-

hanced crop growth (Armada et al., 2014). In vermiculture, vermi-

compost is produced through the artificial cultivation of worms and

is used for crop production as it provides nutrients to the plants.

Inoculation of vermicompost with PGPR had an additive effect on

crop productivity, especially under drought stress due to its effect

on physicochemical and biological properties of soil (Kazeminasab

et al., 2016).

Similarly, nodulation and growth of chickpea were significantly

enhanced with the combined application of phosphorus enriched

compost with Mesorhizobium ciceri and PGPR under normal and

rainfed irrigation systems (Shahzad et al., 2014). Moreover, nutri-

ent contents, enzyme activities such as dehydrogenase, and phos-

phomonoesterase activities significantly enhanced chickpea growth

and productivity under a rainfed irrigation system. In another study,

the combined application of PGPR with compost and mineral fertil-

izer improved growth, physiological and biochemical parameters of

wheat under drought stress (Kanwal et al., 2017).

Recently, nanotechnology has played a significant role in crop

growth and productivity under normal and abiotic stress conditions.

Nanomaterials with smaller sizes have a large surface area, making

them robust for various agricultural applications (Ditta, 2012, 2019;

Ditta & Arshad, 2016; Ditta et al., 2020). In this regard, nano- compost

was prepared via ball mill technology after enriching municipal solid

waste compost with nutrients. The nano- compost was applied with

drought- tolerant PGPR to enhance the growth and productivity

of turfgrass under drought stress (Duo et al., 2018). In results, the

combined application of PGPR with nano- compost significantly al-

leviated oxidative stress under drought, thereby increasing drought

tolerance and ultimately growth and productivity in turfgrass. In the

future, more studies are needed to confirm its effectiveness under

natural field conditions using different crops.

3.5 | Biochar, PGPR, and compost under

drought stress

Since there is positive feedback on the individual role of PGPR,

BC, and compost in enhancing plant growth under normal as well

as drought stress, there is meager information on the interactive

impact of PGPR with BC and compost, particularly under drought

stress (Table 5). Recently, Uzinger et al. (2020) found that combined

application of PGPR with BC and compost significantly enhanced

the microbial activity with the lowest arbuscular mycorrhizal fungi

(AMF) colonization. However, there was a non- significant effect on

the soil fertility level with the combined application of PGPR with

BC and compost. The interactive effect of BC, compost, and PGPR

in improving drought stress tolerance in cucumber was evaluated

by Nadeem et al. (2017). In results, improved cucumber growth

was recorded with the combined application of BC, compost, and

PGPR under drought stress. With the combined application of

ULLA H et AL.

TABLE 3 Impact of biochar and PGPR under Drought Stress

Crop Biochar Inoculum Drought Stress Impact Reference

Maize (Zea

mays)

T i m b e r- w a s t e Pseudomonas aeruginosa,

Enterobacter cloacae,

Achromobacter xylosoxidans

and Leclercia adecarboxylata

Normal moisture (NM) was

maintained at the level of

70% of FC. Mild (MD) and

severe drought stress (SD)

were maintained at 50% and

30% of FC

Grain yield plant−1, photosynthetic rate, stomatal conductance,

chlorophyll a, total chlorophyll and carotenoids contents

were increased up to 60%, 73%, 43%, 69%, 76% and 42%

respectively and grain yield plant−1, photosynthetic rate,

stomatal conductance, chlorophyll a, total chlorophyll and

carotenoids contents up to 200%, 213%, 113%, 152%, 148%

and 284%

Danish

et al. (2020)

Wheat

(Tr it icu m

aestivum)

Timber waste Leclercia adecarboxylata,

Agrobacterium fabrum,

Bacillus Amyloliquefaciens,

Pseudomonas aeruginosa

Polyethylene glycol 6,000

(PEG- 6000) used (0%,

10% and 20%) to maintain

osmotic potential (0.05,

−0.23 and −0.78 MPa) to

introduce drought stress

Combined application improved chlorophyll a, chlorophyll b,

photosynthetic rate, transpiration rate, 100- grain weight, and

grain N, P and K by 114%, 123%, 118%, 73%, 59%, 58%, 18%

and 23%, respectively

Danish and Zafar-

ul- Hye (2019)

Wheat

(Tr it icu m

aestivum)

Timber- waster Agrobacterium fabrum or

Bacillus amyloliquefaciens

Mild drought (three

irrigations were applied (one

irrigation was skipped at

the tillering stage). Severe

drought stress was induced

by using two irrigations (two

irrigations were skipped;

one at the tillering stage and

other at the milky stage)

Combined application of B. amyloliquefaciens and 30 Mg/ha

BC under 3I, significantly increased growth and yield traits

of wheat: grain yield (36%), straw yield (50%), biological yield

(40%). The same soil application under 2I resulted in greater

increases in several of the growth and yield traits: grain yield

(77%), straw yield (75%), above and below- ground biomasses

(77%), as compared to control

Z a f a r - u l - H y e

et al. (2019)

Maize (Zea

mays)

Algal biomass Serratia odorifera One group of plants was

given a water level 75% FC;

another group was given

50% FC while the remaining

group was watered at

normal (100% FC)

Combined application of algal BC and PGPR significantly

increased fresh and dry weights of shoot and root and root

length by 2.76, 5.94, 3.24, 13.82, and 4.06 percent.

Ullah et al. (2020)

Lupin (Lupinus

angustifolius

L.)

Hydrochar from maize silage,

pyrolysis biochar from

maize (MBC) and pyrolysis

biochar from wood (WBC)

Bradyrhizobium sp.Two conditions, namely

irrigated conditions

(watered at 75% FC) and

drought stress (irrigation at

45% FC)

The HTC- based formulation of Bradyrhizobium sp. provides

an effective carrier for inocula, thereby improving growth,

nutrient uptake and symbiotic performance of lupins

under drought. lupins that were treated with HTC- BR had

significantly greater shoot (18%) and root (39%) weights.

Egamberdieva

et al. (2017)

ULLAH et AL.

TABLE 4 Impact of Compost and PGPR under Drought Stress

Crop Compost Inoculum Drought Stress Impact Reference

Wheat ( Tritic um

aestivum)

Biogas slurry

(BGS)

Pseudomonas moraviensis The irrigation was skipped at the

tillering (SIT) and flowering (SIF)

stages of the crop while there

were four irrigations applied

during normal irrigation (NI).

After 15 days of seed sowing

three levels of irrigation were

maintained i.e., 100%, 70% and

50% WHC

The Pseudomonas moraviensis with BGS application improved

the grain yield and plant height up to 30.3% and 24.3%,

respectively, where irrigation was skipped at the tillering

stage, as compared to the uninoculated controls. The same

treatment significantly increased RWC, catalase activity,

ascorbate peroxidase activity, as well as grain and shoot

phosphorus contents, up to 37%, 40%, 75%, 19%, and 84%,

respectively, at SIF

Yaseen

et al. (2020)

Maize (Zea mays) Vermicompost

tea (VT) and

vermiwash (V)

Micrococcus yunnanensis Three levels of water deficit stress

(WDS) (FC, 80% FC and 60% FC)

PGPR enriched liquid organic fer tilizers (LOFs) were more

effec tive and practical approach for amplifying drought

tolerance and reducing the risk of water scarcity in maize

cultivation. At all WDS levels, application of LOFs increased

shoot dry weight and nutrients uptake

Moridi

et al. (2019)

Wheat ( Tritic um

aestivum)

Biogas slurry

(BGS)

Alcaligenes faecalis,

Bacillus amyloliquefaciens

and Pseudomonas

moraviensis

After 15 days of seed sowing

three levels of irrigation were

maintained i.e. 100%, 70% and

50% WHC

ACCD possessing rhizobacterial inoculations with BGS

improved stomatal and sub- stomatal conductance,

transpiration and photosynthetic rates up to 98%, 46%,

38%, and 73%, respectively, compared to the respective

uninoculated controls. The Pseudomonas moraviensis with BGS

application improved the grain yield and plant height up to

30.3% and 24.3%, respectively, where irrigation was skipped

at the tillering stage, as compared to the uninoculated controls

Yaseen

et al. (2019)

Turfgrass (Festuca

arundinacea

Schreb.)

Municipal solid

waste

Bacilluscereus,

Lysinibacillus sp. and

Rhodotorula glutinis

Water was supplied daily to

maintain 75% FC of soil. 20 days

after planting, plants were

exposed to two levels of drought

stress, namely moderate drought

stress (watered and maintained

at 55% FC) and severe drought

stress (watered and maintained at

40% FC) for 40 days

The enhancement in plant biomass was pronounced in plants

treated with both nano- compost and microbial inoculants,

i.e. 210% and 226% increases in shoot and root biomass,

respectively, than control plants under moderate drought

stress. Under severe drought stress, same treatment increased

shoot and root biomass by 209% and 215%, respectively,

compared to the control.

Duo et al. (2018)

Chickpea (Cicer

arietinum)

Farm yard

manure

Mesorhizobium

cicri, Pseudomonas sp. and

Bacillus sp.

Natural desert conditions With the application of biofertilizer, the maximum increase

in number of nodules plant−1 as compared to control was

observed at site 16BC that was 126% higher than control. The

combined application of P- enriched compost and biofertilizer

resulted in maximum increase (230%) in number of nodules as

compared to un- inoculated control at the same site

Ahmad

et al. (2017)

(Continues)

ULLA H et AL.

Crop Compost Inoculum Drought Stress Impact Reference

Wheat ( Tritic um

aestivum)

Food waste Azospirillum

lipoferum

Soil moisture was maintained at

15 ± 1% i.e. 65 ± 5% by weight of

FC, by water holding in drought

exposed plants; and at 19 ± 1%

(i.e. 85 ± 5% by weight of FC) in

well- watered plants. To induce

drought, water was withheld for

ten days at vegetative stages

Inoculated seed with compost and mineral fertilizer grown

in drought condition showed 43% increase in relative water

content (RWC) of 9.39% in membrane stability index and

82.20% in chlorophyll as compared to control. Drought

affected the accumulation of osmolytes, but PGPR in

combination with compost and mineral fertilizer under

drought stress triggered higher accumulation of soluble sugar

and proline content, i.e. 28.96% and 73.91%, respectively

Kanwal

et al. (2017)

Lemon Balm (Melissa

officinalis L.)

Vermicompost Pseudomonas fluorescent,

Azotobacter chrococum,

Azospirillm brasilense

Plants in the drought- stressed

treatment were watered to 60%

of FC same times

Only RWC and total chlorophyll were positively affected

by biofertilizer application while vermicompost enhanced

essential oil content, essential oil yield, total chlorophyll, cell

membrane stability, proline and RWC

Kazeminasab

et al. (2016)

Maize (Zea mays) and

clover

(Trifolium repens)

Sugar beet waste Bacillus megaterium and/or

consortium of arbuscular

mycorrhizal fungi (AMF)

Natural drought conditions with

polyethylene glycol (PEG) (0%, 5%

and 10%) in the culture medium to

induce osmotic stress.

Inoculated residue amended soil promoted plant growth and

hydric content and decreased most antioxidant activities to

a greater extent than AMF inoculation. Comparing the total

shoot plant biomass yielded in control plants with those

amended and inoculated, the highest differences in shoot

biomass were of 157% (BC) and 135% (MC)

Armada

et al. (2014)

Chickpea (Cicer

arietinum)

Fruit and

vegetable waste

and enriched

with single

super phosphate

Mesorhizobium ciceri Irrigated and rainfed farming

systems

Compared to irrigated farming system, inoculation with

phosphorus- enriched compost under rainfed conditions

was more beneficial in improving grow th and nodulation of

chickpea

Shahzad

et al. (2014)

Sesame (Sesamum

indicum)

Organic fertilizer Serratia sp., B. polymyxa

and P. fluorescens

Irrigation water intervals (6, 9 and

12 days

The interaction effect among irrigation water intervals,

compost rates and bacterial inoculation were significant on all

estimated traits

Ismail

et al. (2013)

Cumin (Cuminum

cyminum)

Animal manure Pseudomonas putida and

P. fluorescence

Two irrigation treatments

(rainfall + 3 irrigations as water

stress and rainfall + 6 irrigations

as control)

Enhanced cumin seed and essential oil yields via improving soil

WHC

Seghatoleslami

(2013)

Giant cardon cactus

(Pachycereus pringlei)

Dairy cow

manure

Azospirillum brasilense Cd Natural barren desert soil Addition of small amounts of common compost; 6%– 25% of

the growth substrate gave the best growth response and, to a

lesser extent, so did inoculation with A. brasilense Cd

Bacilio

et al. (2006)

TABLE 4 (Continued)

ULLAH et AL.

BC, compost and PGPR, shoot length, shoot biomass, root length

and root biomass was significantly increased by 88%, 77%, 89%

and 74%, respectively as compared to uninoculated control under

drought stress. Moreover, an increase in chlorophyll and relative

water contents and reduction in electrolyte leakage was also ob-

served with the combined application of BC, compost, and PGPR.

It was also obser ved that BC and comp ost app lied together showe d

the highest population of P. fluorescens which may also help im-

prove the biological properties of the soil. To confirm these results,

more and more extensive studies involving different crops and

under different environmental conditions are required to authen-

ticate these observations. Moreover, the elucidation of different

mechanisms involved using state- of- the- art analytical techniques

is also required.

4 | MECHANISMS OF PLANT GROWTH

PROMOTION OF ORGANIC AMENDMENTS

AND PGPR UNDER DROUGHT STRESS

The application of BC and compost serves as a conditioner to im-

prove the organic matter in the soil, which subsequently enhances

the physicochemical and biological properties of the soil (Figures 2

and 3). The improvement in soil properties develops soil structure,

enhances WHC of the soil, and ultimately improved water use effi-

ciency under drought stress (Hale et al., 2011; Roberts et al., 2010).

BC remains stable in the soil and leads to slow degradation, which

ultimately serves as a long- term carbon source in soil (Lehmann

et al., 2009). The porous structure of BC serves as protection sites

for indigenous and foreign (inoculated) microbes especially PGPR

which directly or indirectly improve soil nutrient availability under

drought stress (Chen et al., 2014; Hale et al., 2014). Moreover, BC

improves soil porosity while decreases bulk density which ultimately

enhances water and nutrient availability to the plants under drought

stress (Chen et al., 2014). In case of compost, similar mechanisms as

in BC improve physicochemical and biological properties of the soil,

and ultimately water and nutrient availability is increased. Both com-

post and BC serve as carbon sources and carrier material for PGPR

(Hale et al., 2014).

PGPR are well renowned for enhancing crop growth and pro-

ductivity under normal and drought stress through various di-

rect and indirect mechanisms (Figure 4). Under drought stress,

PGPR reduce the production of ethylene via ACC- deaminase ac-

tivity. Increased production of ethylene via its precursor 1- amin

ocyclopropane- 1- carboxylic acid (ACC) during drought stress re-

duces root growth and ultimately leads to plant death (Arshad &

Frankenberger, 2002). During ethylene production, S- Adenosyl-

Methionine (SAM) is converted into ACC via ACC- synthase, which

is activ ate d unde r hig her le vels of in dole acet ic aci d (IA A) pro duc ed

und e r ab i o tic st re s s (P a rr a y et a l ., 20 16). PG PR wi th ACC- de am ina s e

are capable of converting ACC into ammonia and α- ketobutyrate,

thereby reducing ethylene production and ultimately enhanced

root growth and better water and nutrient availability especially

TABLE 5 Impact of biochar, compost and PGPR under drought stress

Crop Biochar Compost Inoculum Drought Stress Impact Reference

Maize

(Zea mays L.)

Grain husks

and paper

fibre sludge

Green waste and sewage

sludge from municipalities

Consortium of Bacillus aryabhattai,

Azospirillum brasilense (NF7),

Azospirillum brasilense (242/9),

Paenibacillus peoriae and Arthrobacter

crystallopoietes

The pots were watered

up to 65% of maximum

The combined application of BC,

compost and PGPR did not result in

higher fertility on the investigated

soil. The mixture of compost and

PGPR with 1.5% BC resulted in

35% higher availability of P and

K due to higher microbial activity

relative to BC alone. Only compost

used on its own at 0.5% raised

maize biomass by 2.7 times.

Uzinger et al. (2020)

Cucumber

(Cucumis

sativus)

Pine wood Kelp meal, worm castings,

dehydrated poultry manure

and mycorrhizae

Pseudomonas fluorescens Three water levels i.e.

FC (D0), 75% FC (D1)

and 50% FC (D2)

Combined application increased

shoot length, shoot biomass, root

length and root biomass by 88%,

77%, 89% and 74%, respectively.

Also increase in population of

P. Fluorescens, improved chlorophyll

and relative water contents while

leaf electrolyte leakage was

reduced

Nadeem et al. (2017)

ULLA H et AL.

under dr o ught st ress (S h a h aroon a et al ., 20 06 , 20 07 ) . PG PR ar e al so

known to enhance nutrient availability especially nitrogen through

BNF and P through P- solubilizing activity (Ditta et al., 2015; Ditta,

Imtiaz, et al., 2018; Ditta, Muhammad, et al., 2018). Under drought

stress, another mechanism employed by PGPR is the upregulation

of stress- responsive genes. For example, sbP5CS2 and sbP5CS1 in

sorghum were upregulated with the inoculation of multi- trait PGPR

and ultimately resulted in enhanced growth via induced stress tol-

erance (Govindasamy et al., 2020). Similarly, PGPR inoculation up-

regulated the genes involved in the regulatory component (CTR1)

of the ethylene signaling pathway (Barnawal et al., 2017), lipoxy-

genase pathway, and jasmonic acid pathway (Ahmad et al., 2019),

dehydrin proteins (Borovskii et al., 2002), ROS scavenging (Tiwari

et al., 2016), etc. Other mechanisms include the secretion of or-

ganic acids, production of phytohormones, acting as biocontrol

agents, etc. (Kasim et al., 2013; Rocha et al., 2019; Saharan &

Nehra, 2011).

5 | SUMMARY AND FUTURE

PERSPECTIVES

Under drought stress, reduced growth and development of crops

have been observed in many crops. For the sustainable manage-

me nt of dr ought str ess , it is im por tant to dev elop cer tain strat egies

that are efficient and low- cost to increase crop productivity.

These resource management strategies include the integrated use

of PGPR and organic amendments (compost, and BC). Figure 5

gives an overview of the impacts of drought stress on plants and

its amelioration through economical, environment- friendly, and

sustainable ways. These strategies help reduce environmental pol-

lution due to the usage of various organic wastes for BC and com-

post preparation and are environment- friendly. Numerous studies

have confirmed their efficacy in improving the growth and yield of

crops under drought stress. Algal BC is comparatively low in car-

bon content, surface area and cation exchange capacity, but high

in pH, ash, nitrogen, and extractable inorganic nutrients including

P, K, Ca and Mg. Th ere for e, alg al BC ha s prop erti es that pro vid e di-

rect nutrient benefits to soils and crop productivity under drought

stress.

In the case of integrated use of PGPR, compost and BC, very

few studies have been conducted under normal as well as under

abiotic stress conditions such as drought stress. In the future,

more rigorous studies are required to evaluate their additive ef-

fect during drought stress under field conditions. Moreover, in-

sights into the mechanisms behind the interaction of PGPR and

plants under drought stress need further investigation. For this

elucidation, employing various state- of- the- art molecular ap-

proaches would help find out the mechanisms behind their syn-

ergistic effect.

FIGURE 5 Overview of the impacts of drought stress on plants and its amelioration through economical, environment- friendly and

sustainable way

ULLAH et AL.

DATA AVA ILAB ILITY STATE MEN T

Data sharing not applicable to this article as no datasets were gener-

ated or analyzed during the current study

ORCID

Allah Ditta https://orcid.org/0000-0003-1745-4757

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Incorporation Effect of Lignin and Wheat Straw Biochar on Promoting Maize Growth and Reducing Cd Uptake Under Different Irrigation Regimes

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Jun 2024
WATER AIR SOIL POLL

Cadmium (Cd) contamination of soils is a major agricultural and environmental concern. Biochar (BC) is well known for enhancing crop production, while incorporating lignin (LN) with BC for decreasing Cd uptake and availability has not been studied. Herein, we investigated the effects of LN+BC under different irrigation regimes on Cd uptake, soil properties, and maize growth in Cd-contaminated soil. We used three irrigation regimens as main treatments: 60%, 80%, and 100% of evapotranspiration (ET0). Sub-treatments were soil amendments consisting of 5% BC, 5% LN+BC, and control (CK). Results showed that 60% and 80% irrigation regimens increased Cd concentrations in plant parts while LN+BC application decreased Cd uptake. However, LN+BC and BC significantly decreased Cd uptake across all irrigation regimes. The combination of LN+BC was found to be more efficient in reducing Cd uptake. The order of Cd concentration in plant tissues was as follows: CK > BC > LN+BC. LN+BC significantly increased relative leaf water content (LRWC), membrane stability index (MSI), all growth indicators, and yield attributes compared to CK. Among organic amendments, LN+BC improved grain quality by increasing starch grains, decreasing protein matrix, enhancing side scattered (SSC), and forward scattered (FSC) light signals, followed by BC and CK. The incorporation of LN+BC boosted soil pH, cation exchange capacity (CEC), and organic matter (OM). Combining BC and LN can minimize Cd phytoavailability, enhance soil quality, and boost crop growth in contaminated agricultural soils. This study suggests that a combination of LN and BC can be added as an organic amendment in Cd-contaminated soil.

EPH -International Journal Of Agriculture And Environmental Research EXPLORING THE INFLUENCE OF NANOPARTICLES AND PGPRS ON THE PHYSICO-CHEMICAL CHARACTERISTICS OF WHEAT PLANTS: A REVIEW

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This review explores how plant growth-promoting rhizobacteria (PGPRs) and nanoparticles can improve the physicochemical traits of wheat plants and boost crop yields. Wheat is essential for the world's food supply, but its growth is impacted by factors such as soil quality and climate. The potential for enhancing crop productivity and soil quality with PGPRs is promising. They improve wheat plant photosynthesis, soil fertility, nutrient availability, and antioxidant activity. When nanoparticles and PGPRs are used together, physicochemical characteristics are improved due to their synergistic effects. These environmentally friendly techniques have the potential to encourage the sustainable production of wheat, reduce dependence on synthetic fertilizers and pesticides, and increase soil fertility. However, it is critical to address any possible health and environmental risks associated with their use. Overall, PGPRs and nanoparticles are viable options for increasing wheat crop production and sustainability.

Exogenous Application of β-aminobutyric Acid Improved Water Relations, Membrane Stability Index, and Achene Yield in Sunflower Hybrids Under Terminal Drought Stress

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May 2024
POL J ENVIRON STUD

Sunflower (Helianthus annuus L.) is a major oilseed crop grown for edible oil throughout the world, including Pakistan. Drought stress is the most significant constraint to crop production in a changing climate scenario, and its severity is increasing day by day. Less rainfall and rising temperatures, particularly during the seed-filling phase, reduce achene yield in sunflower hybrids. Exogenous application of β aminobutyric acid (BABA) is effective in reducing the severity of terminal drought stress in many crop plants. Therefore, the present study was conducted to assess the effect of foliar BABA application on the membrane stability, growth, and productivity of sunflower hybrids under induced terminal drought conditions. A pot experiment was carried out to compare the growth and yield potential of two sunflower hybrids, Hysun-33 and NK-Senji, to two levels of water application: normal irrigation (NI) and terminal drought (TD). To combat terminal drought, four BABA concentrations (0, 20, 40, and 60 mM) were used. When compared to NK-Senji, Hysun-33 had the highest SPAD-chlorophyll value, head weight, 100-achene weight, and achene yield. In comparison to normal irrigation terminal drought increased proline content while lowering relative water content, SPAD-Chlorophyll, 100-achene weight, and achene yield. However, under terminal drought, foliar application of β-aminobutyric acid improved relative water content, SPAD-chlorophyll value, head weight, 100-achene weight, and achene yield. When different levels of BABA were used, the application of 60 mM produced 46% more achene yield than the control. A reduced achene yield was obtained under terminal drought which was improved by foliar spraying of 60 mM β-aminobutyric acid which increased in SPAD-chlorophyll value, membrane stability index, relative water content, and 100-achene weight. Overall, the exogenous application of BABA improved water relations, membrane stability index, and achene yield in sunflower hybrids under terminal drought stress.

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May 2024

Background Utilizing rice straw biochar (RSB) presents a novel approach to overcome toxicity of arsenic (As) in agricultural settings. Similarly, silicon (Si) has emerged as an effective agent for overcoming metal stress within agricultural crops. The present study investigates into the syringic application of RSB and Si in ameliorating As-induced stressed in Oryza sativa L. (rice) seedlings. Methods In the present study, we have used different levels of RSB (0, 2.5, and 5% w/w) and Si (0, 1.5, and 3 mM) to O. sativa seedlings when exposed to different levels of As stress i.e., 0, 50 and 100 µM to examine plant growth and biomass, photosynthetic pigments and gas exchange characteristics, oxidative stress indicators, and the response of various antioxidants (enzymatic and non-enzymatic) and their specific gene expression, proline metabolism, the AsA–GSH cycle, cellular fractionation in the plants. Results Our results showed that the increasing concentration of As in the soil significantly (P < 0.05) decreased total plant length, root length, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight by 26, 12, 18, 34, 39 and 20% respectively, compared to the plants which were grown in the 0 µM of As in the soil. Additionally, As stress in the soil increased the concentration of reactive oxygen species (ROS) causes oxidative damaged to membranous bounded organelles, increases organic acids, As concentration, affects antioxidants, proline metabolism, AsA–GSH cycle and cellular fractionation. Although, Although, the application of Si and RSB showed a significant (P < 0.05) increase in plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds, and their gene expression and also decreased oxidative stress. In addition, the application of Si and RSB enhanced cellular fractionation and decreased the proline metabolism and AsA–GSH cycle in O. sativa seedlings. Conclusion These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

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May 2024

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GLOBAL NEST J

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Managing Soil Drought

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May 2024

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Apr 2021

To feed the burgeoning human population, there is dire need to enhance the crops yield. Limited crop production is the result of many biotic and abiotic stress factors. One of the most important factors causing a reduction in crop yield is drought stress. It adversely affects the physiological attributes of crop plants along with a disturbance in biochemistry which ultimately results in yield reduction. Several physicochemical strategies have been recommended by researchers to enhance water stress tolerance among crop plants. These practices are costly and energy-, and labor-intensive. However, biological approaches can be a less expensive, efficient, and ecofriendly strategy to cope with drought stress. Developing varieties with more tolerance against abiotic stresses is a very lengthy process. However, it would be imperative to get benefit from living tiny creatures (rhizobacteria) found in the vicinity of plant roots, that is, rhizosphere. The ability of rhizosphere bacteria to tolerate drought conditions can be used as an effective tool for plant–microbe interactions under drought and or water stress. This chapter highlights the role of rhizobacteria in enhancing drought stress tolerance among crop plants, their mechanisms of action, and prospects.

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Biochar is a carbonic recalcitrant product of biomass which is produced by pyrolysis process. In fact, biochar application has the potential to improve soil properties and crop productivity for long term scenarios compared to many other organic amendments. In this review we have tried to explore the role of biochar in the modification of soil properties (physical, chemical and biological), relevant effects of these changes on crop productivity and its future prospects and challenges by considering the existing literature. Addition of biochar as soil amendment has significantly influenced the soil physical, chemical and biological properties. Biochar application reduces the bulk density of soil, increased microbial activity, pH level and water holding capacity; but it varied according to soil texture. Furthermore, increase in soil porosity and infiltration rate has also been observed due to biochar addition. Simultaneously, biochar addition sometimes could have negative impacts on soil properties that appear in the form of crop productivity loss. This study will provide a clear picture about the role of biochar in modifying soil properties and its beneficial impacts on crop growth and yield.

Fertility Impact of Separate and Combined Treatments with Biochar, Sewage Sludge Compost and Bacterial Inocula on Acidic Sandy Soil

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Full-text available

Oct 2020

The short-term effects of processed waste materials: sewage sludge compost (up to 0.5%), biochar made of paper sludge and grain husk (BC) (up to 2%) combined with plant growth-promoting rhizobacterial (PGPR) inoculum, on the fertility of acidic sandy soil at 65% of field capacity were tested in a pot experiment in separate and combined treatments. The soil pH, organic matter content, total and plant-available nutrients, substrate-induced respiration, arbuscular mycorrhizal fungal (AMF) root colonisation parameters and maize (Zea mays L.) biomass were investigated in experiments lasting two months. The positive priming (21% organic matter loss) induced by BC alone was not observed after combined application. The combination of compost and PGPR with 1.5% BC resulted in 35% higher P and K availability due to greater microbial activity compared to BC alone. Only compost applied alone at 0.5% gave a 2.7 times increase in maize biomass. The highest microbial activity and lowest AMF colonisation were found in combined treatments. In the short term the combined application of BC, compost and PGPR did not result in higher fertility on the investigated soil. Further research is needed with a wider range of combined treatments on acidic sandy soil for better understanding of the process.

Biochar Reduced Cadmium uptake and Enhanced Wheat Productivity in Alkaline Contaminated Soil

Article

Full-text available

Sep 2020

Cadmium (Cd) is a toxic heavy metal present in the environment which causes severe environmental, nutritional, and ecological losses. A pot incubation study was conducted to assess the role of biochar derived from various organic feedstock’s [poultry manure (PM), farmyard manure (FYM) and sugarcane press mud (PS)] and dosages (0, 2.5 and 5 g kg-1 soil of each) to immobilize Cd (5 mg kg-1) in Cd polluted soil. Moreover, impact of applied biochar to reduce the bioavailability of Cd in wheat tissues and to improve wheat growth and yield was also observed. Among all type of applied biochar, application of farmyard manure (FYM) derived biochar improved tillers population (77%), chlorophyll SPAD value (74%), plant height (69), grains yield (77%) and biological yield (82%) of wheat. Moreover, FYM derived biochar lowered the Cd uptake and its translocation from roots (71–92%) shoots (82–92%), and grains (90–96%) as compared with control. While in Cdcontaminated soil without biochar application, the Cd concentration in roots, shoots and grains were 1.4, 1.14 and 0.9 mg kg-1 of dry matter, respectively. Overall, FYM derived biochar, applied at 5 g kg-1 of soil performed better in reducing the Cd toxicities in soil (0.12 mg kg-1) and wheat roots (0.13 mg kg-1), shoots (0.1 mg kg-1) and grains (0.03 mg kg-1) along with higher wheat yield in Cd polluted soil. In conclusion, FYM derived biochar has the potential to remediate Cd toxicities in alkaline polluted soil.

Ameliorating the Drought Stress for Wheat Growth through Application of ACC-Deaminase Containing Rhizobacteria along with Biogas Slurry

Article

Full-text available

Jul 2020

The temperature increase around the world is leading to generation of drought, which is a big threat to the productivity of crops. Abiotic stresses like drought increase the ethylene level in plants. In higher plants, 1-aminocyclopropane-1-carboxylate (ACC) is considered as the immediate precursor of ethylene biosynthesis. The application of ACC-deaminase (ACCD) possessing rhizobacteria could ameliorate the harmful results of drought stress by transforming ACC into non-harmful products. Biogas slurry (BGS) improves the water-holding capacity and structure of the soil. Thus, we speculated that the integrated application of ACCD possessing rhizobacteria and BGS might be an efficient approach to mitigate the drought stress for better wheat productivity. A field experiment was conducted under skipped irrigation situations. On the tillering stage (SIT) and flowering stage (SIF), the irrigations were skipped, whereas the recommended four irrigations were maintained in the control treatment. The results of this field experiment exposed that the ACCD possessing rhizobacterial inoculations with BGS considerably improved the stomatal and sub-stomatal conductance, transpiration and photosynthetic rates up to 98%, 46%, 38%, and 73%, respectively, compared to the respective uninoculated controls. The Pseudomonas moraviensis with BGS application improved the grain yield and plant height up to 30.3% and 24.3%, respectively, where irrigation was skipped at the tillering stage, as compared to the uninoculated controls. The data obtained revealed that the P. moraviensis inoculation + BGS treatment significantly increased the relative water Sustainability 2020, 12, 6022 2 of 18 content (RWC), catalase (CAT) activity, ascorbate peroxidase (APX) activity, as well as grain and shoot phosphorus contents, up to 37%, 40%, 75%, 19%, and 84%, respectively, at SIF situation. The results depicted that the P. moraviensis with BGS application under drought stress could be applied for enhancing the physiological, yield, and growth attributes of wheat.

Biochar Mitigates Combined Effects of Drought and Salinity Stress in Quinoa

Article

Full-text available

Jun 2020

Abiotic stresses such as drought and salinity constantly threaten food security. Biochar as a soil amendment has the potential to ameliorate soil and alleviate drought and salinity stress. Multiple studies have been conducted to evaluate the effect of biochar in alleviating independent drought or salinity stress. However, the potential of biochar in mitigating the combined drought and salinity stress on plants has not been studied so far. Therefore, a pot experiment was conducted in the climate-controlled chamber with the objective to investigate the effect of biochar on growth, physiology, and yield of quinoa under independent and combined drought and salinity stress. Quinoa plants were subjected to three irrigation treatments i.e., full irrigation (FI), deficit irrigation (DI), and alternate root-zone drying irrigation (ARD), two saline water treatments (0 and 400 mM) and two levels of biochar (0% and 5% by weight). In the FI treatment, plants were irrigated daily to maintain pot water-holding capacity. In limited irrigation treatments, 70% water of FI was applied either to the whole pot in DI or to one side of the pot alternating in ARD, respectively. The results showed that combined drought and salinity stress drastically affected growth and performance of quinoa compared to the independent drought or salinity stress. However, soil amendment with biochar had positive effect in mitigating both independent and combined effect of drought and salinity on quinoa plants. Furthermore, biochar amendment in ARD under salinity significantly enhanced plant height, shoot biomass, and grain by 11.7%, 18.8%, and 10.2% as compared with DI under salinity, respectively. In addition, leaf photosynthetic rate (An) and stomatal conductance (gs) decreased under limited saline irrigation. Moreover, the interactive effect of biochar and ARD efficiently adjusted the balance between chemical signal (leaf ABA) and hydraulic signal (leaf water potential). Thus, intrinsic water use efficiency (WUEi) and yield in ARD were significantly enhanced compared to DI, especially under salinity stress. Overall, biochar in combination with ARD might be a wise approach for sustaining crop productivity in salt affected and drought stressed areas of the world to ensure food security.

Greater, but not necessarily better: The influence of biochar on soil hydraulic properties

Article

Mar 2021

Biochar is recommended as a soil amendment for its positive influence on soil hydrological properties, which results in improved soil fertility and crop yield. Much research in the last decade has been conducted in field and laboratory conditions on the effect of biochar on the hydraulic properties of soil. However, reported results in the literature are substantially inconsistent. Here we performed a meta‐analysis to capture the variations in change in hydraulic properties of arable soils after application of different rates of biochar. The meta‐analysis revealed that high biochar rates (>50 t ha ⁻¹ ) compared to low rates (<20 t ha ⁻¹ ) significantly improved dry bulk density in sandy and clay soils, in field and laboratory experiments. However, field capacity only improved in laboratory experiments on sandy soils. The plant available water, permanent wilting point and saturated hydraulic conductivity did not significantly increase at high rates of biochar application compared to the low rates when applied to different types of soils in both field and laboratory experiments. We discuss possible reasons for this, including hydrophobicity of the biochar with future research directions. We concluded that the current evidence does not support the notion that the application of biochar improves soils' available water capacity. Highlights Meta‐analysis clarifies the influence of biochar on soil hydraulic properties. Biochar addition at higher rates only improves the water holding capacity of sandy soils. Biochar types and pyrolysis temperatures do not influence soil hydraulic properties. The efficiency of biochar may depend on its pore size distribution and hydrophobicity.

Immobilization of Pb and Cu by organic and inorganic amendments in contaminated soil

Article

Mar 2021
GEODERMA

Soil contamination with heavy metals has become a global environmental-health concern. A series of greenhouse experiments were conducted to investigate the effects of rice straw, rice straw derived biochar (BC), multi-walled carbon nanotubes, and single superphosphate (SSP) on immobilization of Pb and Cu via sequential extraction of BCR, total characteristics leaching procedure (TCLP), and metals phytoavailability to rapeseed in Pb and Cu spiked soil. Moreover, the residual effect of applied soil amendments on growth and uptake of Pb and Cu in tomato was also investigated in the metals spiked soil. In results, the addition of BC to Pb and Cu spiked soil proved the most effective amendment in modifying the distribution pattern of Pb and Cu from acid-soluble (less bioavailable) to residual fraction (non-toxic), thereby improving the geochemical stability of contaminated soil. The application of BC (6% w/w) reduced the uptake of Pb and Cu in shoot and root by 46 and 36%, and 77 and 58%, respectively. While investigating the residual impact in tomato, the uptake was decreased by 36 and 66% for Pb and 29 and 61% for Cu in shoot and root samples, respectively. With the application of BC (6% w/w), the concentrations of Pb and Cu in the shoot portion of tomato were below the permissible limits as set by the world health organization. The application of SSP was more effective in reducing TCLP-Pb to 0.2 mg L − 1 in metals spiked soil compared to the other amendments. However, the bioavailability of Cu was increased with increasing SSP addition. In conclusion, the application of BC was more effective in reducing Pb and Cu phytoavailability through immobilization in contaminated soil compared to the other organic and inorganic amendments.

Drought stress effect on polyphenolic content and antioxidant capacity of cowpea pods and seeds

Article

Oct 2020
J AGRON CROP SCI

Cowpea (Vigna unguiculata L. Walp) is a protein‐rich grain legume with high adaptability to heat and drought and can be consumed during all stages of the plant development. Drought is a severe environmental stress with major impacts on plant development and productivity. This study main objective was to understand the effects of drought stress on polyphenolic content and antioxidant capacity in plant tissue at different stages of cowpea development. Four cowpea genotypes grown until the anthesis under well‐irrigate conditions and then were submitted to two watering regimens (0% and 75% of field capacity) for one week. Immature pods and seeds and dry seeds were collected, and polyphenolic content and antioxidant capacity were evaluated by spectrophotometry. In general, differences between genotypes, plant growth stage and treatments were observed. A variation of phenolic content and antioxidant capacity has been detected in all cowpea genotypes and plant tissues at different development stages. Immature pods showed the highest values in all the parameters evaluated, while the dry seed presented the lowest values. The samples submitted to drought stress showed a slight decrease in all the parameters evaluated compared to control samples being this decrease only significant in some parameters and growth stages. This study shows that drought stress did not significantly influence the quality of cowpea through phenolic content and antioxidant capacity.

Physiological performance of soybean genotypes grown under irrigated and rainfed conditions

Article

Sep 2020

Gas exchange analysis is an important technique, as the reduction in yield may be related to the decreased photosynthetic activity, due to adverse climatic factors in the growing site. The hypothesis of this study was that contrasting soil water conditions result in different photosynthetic performance in soybean genotypes. Thus, our objective was to analyse the physiological capacity in soybean genotypes under field conditions with optimal soil moisture and under water deficit. The experimental design was random blocks with 10 genotypes (P1, P2, P3, P4, P5, P6, P7, P8, P9 and P10) and three replicates. Individual analysis of variance was performed in both environments (irrigated and rainfed), and a correlation network between the traits was generated. We measured the traits net photosynthesis, stomatal conductance, internal CO2 concentration, instant water‐use efficiency, instant carboxylation efficiency and grain yield. Stressed plants reduce stomatal conductance and transpiration, but increase the instant water‐use efficiency as a defence mechanism in sub‐optimal soil moisture conditions. The P6 genotype obtained better physiological capacity under irrigated conditions, while the P10 genotype showed the better performance under rainfed conditions, which makes it tolerant to water stress. Our findings can contribute to the genotype formation and parental choice steps in breeding programs aimed at obtaining both irrigation‐responsive and drought‐tolerant genotypes.

Appraisal for organic amendments and plant growth-promoting rhizobacteria to enhance crop productivity under drought stress: A review

Abstract

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