Waterlogging and its impact on wheat/Ashwani Kumar, Rajesh Kumar, Jogendra Singh, Pooja and Vijayata...

7/27/2019 Waterlogging and its impact on wheat/Ashwani Kumar, Rajesh Kumar, Jogendra Singh, Pooja and Vijayata Singh

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Waterlogging and its impact on wheat

Ashwani Kumar1, Rajesh Kumar1, Jogendra Singh1, Pooja2 and Vijayata Singh1

1Central Soil Salinity Research Institute, Karnal-132001(Haryana)

2Sugarcane Breeding Institute, Regional Station, Karnal-132001(Haryana)

Waterlogging is a widespread problem for wheat production, especially in the

sodic/alkaline soils of India. Waterlogging is a well known problem in alkali and saline alkali soil

of wheat growing area of Indo-Gangetic plain of India. Around 3.77 mha of sodic soil along with

2.96 mha area adjoin to seepage fed area under extensively circulated irrigation canal network

are severely affected by undesirable waterlogging during wheat season and claim drastic yield

harvesting potential (Yaduvanshi et al., 2012).

Waterlogging is caused by the same processes as dry land salinity. The difference is that

salts do not accumulate at the soil surface, either because ground water is of very low salinity

(less than 6 dS/m) or it flows out of the soil (i.e. from a small spring), flushing the salts away.

Waterlogging problems can also be ephemeral, such as when a perched water table develops on

impermeable sub-soil in a wet season. Most of the information given in this chapter is also

directly relevant to management of waterlogging, except the references to salt accumulation and

its effects. Thus waterlogging will generally not be discussed separately.

Fig. 1: Farmers field affected by salinity, sodicity and waterlogging in India


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In agriculture, various crops need air(specifically, oxygen) to a greater or lesser depth in

the soil. Waterlogging of the soil stops air getting in. How near the water table must be to the

surface for the ground to be classed as waterlogged varies with the purpose in view. A crop's

demand for freedom from waterlogging may vary between seasons of the year, as with the

growing ofrice (Oryza sativa).

In irrigated agricultural land, waterlogging is often accompanied by soil salinity as

waterlogged soils prevent leaching of the salts imported by the irrigation water. From

a gardening point of view, waterlogging is the process whereby the soil blocks off all water and is

so hard it stops air getting in and it stops oxygen from getting in.

Hypoxia and anoxia

Hypoxia or oxygen depletion is a phenomenon that occurs in soil environments as

oxygen in soil air becomes reduced to a point below optimum level. In plant physiological

studies, the term hypoxia is reserved for situations in which the oxygen concentration is a

limiting factor (Morard and Silvestre, 1996). It is usual form of stress in soil that experiences

long-term flooding or waterlogging. It occurs in plants completely submerged by water, and

in deep roots below flood waters (Sairam et al., 2008).

How does waterlogging induce hypoxia and anoxia?

One of the most important properties of soil is soil aeration which relates to the ability of

soils to exchange gases with the atmosphere. This exchange is usually achieved primarily

through diffusion of gasses from and to the soil via pore spaces in the soil. In most well drained

soils, the air-filled pore spaces make up 10 to 40% of total soil volume. Waterlogging eliminates

these gas-filled pore spaces and cuts the supply of oxygen to the roots to a large extent

(Ponnamperuma, 1972). In the waterlogged soil, micro channels for gas diffusion among soil

particles or aggregations become sealed with water, which results the gas diffusivity in soil

104 times lower than in well-drained soil (Armstrong, 1979; Ponnamperuma, 1984).

The lower gas diffusivity between ambient air and waterlogged soil results in low O2

concentration (hypoxia) and high toxic gas concentration, such as CO2 and reduced gases

(Ponnamperuma, 1972, 1984). Moreover, gases formed by soil metabolism, including carbon

dioxide, start to accumulate near root surfaces (Setter and Belford, 1990). The gas exchange
http://en.wikipedia.org/wiki/Crophttp://en.wikipedia.org/wiki/Earth's_atmospherehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Ricehttp://en.wikipedia.org/wiki/Irrigationhttp://en.wikipedia.org/wiki/Soil_salinityhttp://en.wikipedia.org/wiki/Soil_salinity_controlhttp://en.wikipedia.org/wiki/Sodium_chloridehttp://en.wikipedia.org/wiki/Gardeninghttp://en.wikipedia.org/wiki/Crophttp://en.wikipedia.org/wiki/Earth's_atmospherehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Ricehttp://en.wikipedia.org/wiki/Irrigationhttp://en.wikipedia.org/wiki/Soil_salinityhttp://en.wikipedia.org/wiki/Soil_salinity_controlhttp://en.wikipedia.org/wiki/Sodium_chloridehttp://en.wikipedia.org/wiki/Gardening


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between soil and atmosphere almost stops as soon as the waterlogging sets in. The soil microbes

and plant roots use up the oxygen trapped in the soil and therefore, the roots may become

exposed to complete lack of oxygen (anoxia) (Jackson and Drew, 1984). However, under natural

conditions, oxygen concentration decreases gradually, and hence, anoxia is always preceded by

hypoxia (Setter and Waters, 2003) in waterlogged environment.

Mechanisms of tolerance of wheat to waterlogging

Waterlogging tolerance is defined as the survival or the maintenance of plant growth at

high rates under waterlogged conditions relative to well drained conditions. It may be defined as

the maintenance of relatively high grain yields under waterlogged conditions relative to non- or

less-waterlogged conditions (Setter and Waters, 2003).

Morphological and Metabolic adaptation

A. Morphological adaptation

(i) Root growth

A common adaptation of plants to waterlogging is the survival and growth of seminal roots

and production of numerous adventitious roots with aerenchyma. The root growth in

waterlogging intolerant genotypes is drastically suppressed by waterlogging stress. However, thetolerant genotypes have the ability to continue their root growth under the stress in some extent.

The above hypoxic stress had no significant effect on the growth of seminal roots for tolerant

genotypes (Gore and Savannah). Total root dry mass was reduced for all genotypes except for

Savannah (Huang et al., 1994a). However, the waterlogging tolerance of a plant is determined

not only by its capability to undergo morphological adaptations, but also by the ability to recover

from transient waterlogging or hypoxia of the root system (Krizek, 1982; Huang et al., 1994a,

1997).

(ii) Aerenchyma formation and increased root porosity

Aerenchyma is a special tissue which consists of continuous gas filled channels or much

enlarged gas spaces, and root porosity is volume of gas-filled spaces in relation to the total tissue

volume. Aerenchyma provides a low resistance internal pathway for the movement of O2 from


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the shoots to the roots (Armstrong, 1979) Armstrong and Webb, 1985; Drew et al., 1985).

Aerenchyma tissue in roots allows the roots to respire aerobically and to maintain growth under

hypoxic conditions. Moreover, a part of oxygen transported to plant root tips through the

aerenchyma leaks out into the surrounding soil and results in a small zone of oxygenated soil

around the roots providing an aerobic environment for microorganisms that can prevent the

influx of potentially toxic soil components such as nitrites and sulphides of Fe, Cu and Mn.

Therefore, aerenchyma formation is thought to be one of the most important morphological

adaptations for the tolerance to hypoxic or anoxic stress. Under oxygen deficient condition,

ethylene production is accelerated which in turn stimulates aerenchyma formation in adventitious

roots and induces the growth of the roots (Drew et al., 1979; Jackson, 1989).

However, the conversion of ACC to ethylene requires oxygen and the conversion

reaction is blocked in an anaerobic root cell. The ACC is therefore, translocated from the

anaerobic root cells towards the more aerobic portions of the root or to the shoot. The lower

portions of the stems are usually the site of highest ACC accumulation and in the

presence of oxygen ethylene is released (Sairam et al., 2008). Formation of aerenchyma has

been observed in the roots of wheat when grown under low O2 concentrations.

Fig. 2: Main physico-chemical events taking place in the rhizosphere during soilwaterlogging and the resulting modifications in plant metabolism and physiology followed

by the initiation of adaptive responses.


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(iii) Barriers to radial oxygen loss

Oxygen in aerenchymatous roots may be consumed by respiration or be lost to the

rhizosphere via radial diffusion from the root. The flux of oxygen from roots to rhizosphere is

termed as radial oxygen loss (ROL) which usually oxygenates the rhizosphere of the plants

growing in waterlogged soils (Armstrong, 1979). However, ROL decreases the amount of O2

supply to the apex of roots that solely depends on aerenchymatous O 2 and, therefore, would

decrease the root growth in hypoxic or anoxic environment (Armstrong, 1979; Jackson and

Drew, 1984).

It is suggested that the loss in internal O2 contributes the poor growth of adventitious roots

and intolerance of wheat to waterlogged soil (Thomson et al., 1992). In contrary, waterlogging

tolerant rice not only has a larger volume of aerenchyma, but it also has a strong barrier to ROLin basal regions of its adventitious roots and therefore deeper root penetration into waterlogged

soil. However, some wheat genotypes can increase suberin or lignin on epidermis or exodermis

of root which may acts as barriers to ROL and results in increased tolerance to waterlogging.

B. Metabolic adaptation

The plant tissue under hypoxia or anoxia suffers from energy crisis (Gibbs and Greenway,

2003) due to reduced root respiration in both waterlogging-tolerant and intolerant plants

(Marshall et al., 1973; Lambers, 1976; Drew 1983, 1990). The tolerant plant species cope with

the energy crisis through metabolic adaptation to oxygen deficiency. The metabolic adaptations

to oxygen deficiency includes: anaerobic respiration, maintenance of carbohydrate supply for

anaerobic respiration, avoidance of cytoplasmic acidification and development of anti-oxidative

defense system

Anaerobic respiration

Plant cells produce energy in presence of oxygen through aerobic respiration which

includes glycolysis, TCA or Krebs cycle and oxidative phosphorylation (Fig. 1). In absence of

oxygen (under anoxic condition), Krebs cycle and oxidative phosphorylation are blocked, and

cells inevitably undergo anaerobic respiration to fulfill the demand for energy (Davies, 1980).


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Mechanisms of tolerance of wheat to waterlogging

Exposure of plants to most adverse conditions like hypoxia or anoxia causes oxidative

stress, which affects plant growth due to the production of reactive oxygen species (ROS) such as

superoxide radicals, hydroxyl radicals and hydrogen peroxide (Mittler et al., 2004). These ROSare very reactive and cause severe damage to membranes, DNA and proteins (Bowler et al.,

1992; Foyer et al., 1997). Hypoxia stress triggers the formation of ROS and induces oxidative

stress in plants.

The tolerance to the stress may be improved by increased antioxidant capacity. Many

recent attempts to improve stress tolerance in plants have been made by introducing and

expressing genes encoding enzymes involved in the antioxidative defense system. Moreover, the

end-products of glycolytic and fermentative pathway, such as ethanol, lactic acid and carbondioxide pose an additional hazard to the cell. It is well reported that the maintenance of an active

glycolysis and an induction of fermentative metabolism are adaptive mechanisms for plant

tolerance. This induction can improve or at least sustain the glycolytic rate in anoxic plants

contributing higher tolerance to anoxia.

Increased availability of soluble sugars

Due to shifting of energy metabolism from aerobic to anaerobic mode under hypoxia or

anoxia the energy requirements of the tissue is greatly restricted as very few ATPs are generated

per molecule of glucose. A high level of anaerobic metabolism in hypoxic or anoxic roots is

therefore very important to supply the energy charge high enough which can sustain metabolism

in roots for the survival of plants (Jackson and Drew, 1984). The roots of comparatively tolerant

genotypes contain greater sugar content (total, reducing and non-reducing sugar) than

in susceptible genotypes of wheat.

Adverse effect of water logging

The adverse effects of waterlogging on wheat are due to decrease availability of oxygen

and accumulation of phytotoxins, severe energy deficiency and ultimately death of plant. The aim

of this study was to evaluate the effect of flooding in field and micro plots of wheat growth stage

under alkali soil and normal soil.


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Depletion of oxygen in root zone and increase of CO 2 due to water logging. An aerobic

condition adversely affects micro-organisms while harmful organisms proliferate and restrict the

plant growth. Physical or chemical and biological activities in the soil are disturbed due to low

temp as a result of water logging. Thus pest and diseases infestation problem arises. Water

logging makes field operations difficult on impossible. The adverse effects of water logging get

accelerated when the capillary water brings salts from lower horizon of soil or they are present in

the ground water used for irrigation. Water logging adversely affect the soil water plant

relationship there by creating ecological imbalance. Crops yields reduced and some time crop

failure due to inadequate uptake of moisture and nutrients and due to the injurious effect of salts or

deteriorated soil condition. Fodders grown in slat-affected soils may contain high molybdenum in

or selenium and low amount of zinc. The nutritional imbalance may cause disease in live stock.

The adverse effects of waterlogging on plants are often ascribed to decreased availability

of O2 and accumulation of phytotoxins (Armstrong and Armstrong 2001). Oxygen deficiency

inhibits aerobic respiration, resulting in severe energy deficiency and eventually death (Greenway

and Gibbs 2003). In addition, waterlogging can also reduce the availability of some essential

nutrients, e.g. nitrogen, and increase the availability of nutrients, e.g. Fe and Mn (Ponnamperuma

1972). Such increases in micronutrients in soil and subsequently in shoots may affect plants both

during waterlogging and also after waterlogging during recovery, as higher micronutrient

concentrations in shoots have been reported during recovery period when soils have returned to

fully aerated conditions (Setter and Waters 2003).

Management options to control waterlogging in crops

1. Drainage is usually the best means of managing waterlogging. Other management options

include: choice of crop, seeding, fertilizer, weed and disease control. Typically, with

changes to crop rotations and management, major costs would include cost of buying seed

and extra fertilizer, and the costs of weed and insect control. Some species of grains are

more tolerant than others. Grain legumes and canola are generally more susceptible to

waterlogging than cereals andfaba beans.

2. Seeding crops early and using long-season varieties help to avoid crop damage from

waterlogging. Crop damage is particularly severe if plants are waterlogged between


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germination and emergence. Increase sowing rates in areas susceptible to waterlogging to

give some insurance against uneven germination, and to reduce the dependence of cereal

crops on tillering to produce grain. Waterlogging depresses tillering. High sowing rates

will also increase the competitiveness of the crop against weeds, which take advantage of

stressed crops.

3. Crops tolerate waterlogging better with a good nitrogen status before waterlogging occurs.

Applying nitrogen at the end of a waterlogging period can be an advantage if nitrogen was

applied at or shortly after seeding has been lost by leaching or denitrification. However,

nitrogen cannot usually be applied from vehicles when soils are wet, so consider aerial

applications.

4. If waterlogging is moderate (730 days waterlogging to the soil surface), then nitrogen

application after waterlogging events when the crop is actively growing is recommended

where basal nitrogen applications were 050 kg N/ha. However, if waterlogging is severe

(greater than 30 days to the soil surface), then the benefits of nitrogen application after

waterlogging are questionable. Weed density affect a crop's ability to recover from

waterlogging. Weeds compete for water and the small amount of remaining nitrogen,

hence the waterlogged parts of a paddock are often weedy.

5. Root diseases, particularly take-all of wheat and barley, are often more severe in

waterlogged crops because the pathogens tolerate waterlogging and low oxygen levels

better than the crops.

Concentrations of oxygen rapidly decreased after the commencement of waterlogging, but

increased again after drainage. If waterlogging is suspected in your crop:

Dig shallow holes 30 to 40 cm deep in winter to see whether any free water is within 30cm of the surface (if so, the soil is waterlogged).

Observe where soils are boggy and crops are yellow.

Mark out the areas that are affected, either with posts laid on the ground or on an accurate

map.

At harvest time observe where the crops are poor and check this against earlier


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Observations.

Survey seepage interceptor drains, placing them immediately above affected sites or

consider raised beds.

Install drains when the soils are moist (for example, after summer or autumn rains).

If installing raised beds, seek further advice from DAFWA or other professionals on

placement and design.

Reference

Armstrong J, Armstrong W. (2001). An overview of the effects of phytotoxins on Phragmites australis

in relation to die-back. Aquatic Botany. 69, 251-268.

Fried A, Smith N. (1992) Soil structure deficiency in extensive croplands of northern Victoria. Land

Degradation Study Group. Soil and Water Group Association of Victoria.

Gill KS, Qadar A, Singh KN. (1992). Effect of wheat (Triticum aestivum) genotypes to sodicity in

association with waterlogging at different stages of growth. Indian Journal of Agricultural Sciences.

62, 124-128.

Greenway H, Gibbs J. (2003). Mechanisms of anoxia tolerance in plants. II. Energy requirements for

maintenance and energy distribution to essential processes.Functional Plant Biology 30, 999- 1036.

Gupta VK. (2004). Soil analysis for available micronutrients. In Methods of Analysis of Soils, Plants,

Watersand Fertilizers. (Ed HLS Tondon) pp. 36-48. (Fertilizer Development and ConsultationOrganization:New Delhi).

Hamilton G, Bakker D, Houlebrook D, Spann C. (2000). Raised beds prevent waterlogging and

increaseproductivity. Western Australia Journal of Agriculture. 41, 3-9.

Lindsay WL, Norvell WA. (1978). Development of a DTPA soil test for zinc, iron, manganese and

copper. Soil Science Society of America Journal. 42, 421-428.

McFarlane D. (1990). Agricultural waterlogging A major cause of poor plant growth and land

degradation in Western Australia.Land and Water Research News 7, 5-11.

National Remote Sensing Agency (NRSA) and Associate (1996) Mapping salt affected soils of India,

1:250,000 mapsheets, Legend. (NRSA: Hyderabad, India).

Patrick WH. (1964). Extractable iron and phosphorus in a submerged soil at controlled redox potentials.

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