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TEMPERATURE | FROST | WATERLOGGING AND FLOODING | DROUGHT


WESTERN

NOVEMBER 2017


SECTION 14

ENVIRONMENTAL ISSUES


FABA BEAN


1 ENVIRONMENtAl ISSUES


seCtIon 14 FABA BEANS


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NOVEMBER 2017


Environmental issues

Key messages

• Frost damage is not always obvious and crops should be checked 5–7 days


after a suspected frost.

• Faba beans have a medium tolerance to frost due to their thick pod walls.

• Faba beans are the pulse most tolerant to waterlogging.

• Disease resistance is especially important in drought-prone areas.


14.1 temperature


Temperature, daylight, day length, and drought are the major factors affecting

flowering in faba beans. Temperature is generally more important than day length.

Flowering is invariably delayed under low temperatures but more branching occurs.


Progress towards flowering is rapid during long days. With short days, flowering is

delayed but never prevented. However, some faba bean varieties are less sensitive

to day length than others. This has enabled breeders to identify varieties that flower

early in the short-day winter growing season in southern Australia. 1


High temperatures

Separating the effects of very high temperature from those of water stress is difficult,

because in rain-fed agriculture, they nearly always occur together.


There is, however, no doubt that high temperature is damaging: in all pulses, high

temperature will cause premature cessation of flowering, and shedding of flowers

and young pods. Planting early maturing faba beans, field peas, and lentils is an

effective strategy to escape high temperature. 2


Temperature and sowing time

The timing of sowing largely determines the timing of the crop’s finish and the

temperature environment in which it will finish.


Plants sown before the recommended sowing window tend to be more vegetative

and suffer from:

• poor early podset because of low light or low temperatures (10°C) at flowering


commencement

• higher risk of chocolate spot at flowering and through podding

• crops being more pre-disposed to lodging

• increased frost risk at flowering and early podding

• high water use prior to effective flowering and the earlier onset of moisture


stress during flowering and podding


Late-planted crops are more likely to suffer from:

• high temperatures and moisture stress during flowering and podding

• greater pressure from native budworms

• fewer branching and flowering sites, unless plant population is increased

• shorter plants and lower podset, which makes plants more difficult to harvest 3


1 Pulse Breeding Australia (2013) Southern/Western Faba & Broad Bean–Best Management Practices Training Course. Module 3–

Varieties


2 DAWA (2005) Producing pulses in the northern agricultural region. Bulletin 4656. Department of Agriculture, Western Australia.


3 Pulse Breeding Australia (2013) Southern/Western Faba & Broad Bean–Best Management Practices Training Course. Module 3–

Varieties.


mailto:GrowNotes.West%40grdc.com.au?subject=


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14.2 Frost


Frost is a complex and erratic constraint to Western Australian (WA) cropping

systems, and can have dramatic consequences to a grower’s business. Research that

investigated trends since the 1960s has shown that:

• WA’s frost window has widened, and on average frosts start three weeks earlier


and finish 2 weeks later in the year.

• Consecutive frost events have increased by an average of up to three days at a


time and mostly occur in August and September in the frost-prone regions.

• The frosts are getting colder, with minimum temperatures dropping. 4


The sequence of weather events that typically generate damaging frosts is

composed of the passage of a weak cold front, followed by cold southerly winds

and the establishment of a ridge of high pressure. This results in cool daytime

temperatures, light winds and clear skies overnight. 5


Faba beans have a medium tolerance to frost due to their thick pod walls, which

provide insulation to the developing seeds, but they are still quite susceptible

to flower, yield and quality losses when frost intensity or duration is severe.

Symptoms include:

• Growing points are sometimes distorted (bent) during early vegetative and


flowering stages. This weakens the cells of the stem, allowing disease such as

chocolate spot to invade easily.


• Flowers are killed by frost, leaving only a flower stalk.

• White or green mottling, and blistering of pods.

• Seeds developing in the pod are shrivelled or absent.

• Affected pods feel spongy and the seeds inside turn black. 6


Tolerance to low temperature

Sub-zero temperatures in winter can damage the leaves and stems of the plant.

Severe frosts can cause a characteristic ‘hockey-stick’ bend in the stem (Photo 1).

However, faba beans have some ability to recover from this damage by being able

to regenerate new branches. New growth occurs from the base of the frost-affected

plants if moisture conditions are favourable.


Photo 1: Severe vegetative frost can cause bends like a hockey stick in faba bean

stems and branches in northern Australia.

Photos: G Cumming, Pulse Australia


Frosts can also cause flower, pod and seed abortion. Pods at a later stage of

development are generally more resistant to frost than flowers and small pods (Photo

2), but may suffer some mottled darkening of the seed coat (Photo 3).


4 GRDC (2016) Pre-seeding planning to manage frost risk in WA. GRDC Media Centre, https://grdc.com.au/Media-Centre/Hot-Topics/

Preseeding-planning-to-manage-frost-risk-in-WA


5 DAFWA (2016) The science of frost. Department of Agriculture and Food, Western Australia, https://www.agric.wa.gov.au/frost/science-

frost


6 DAFWA (2016) Frost: diagnosing the problem. Department of Agriculture and Food, Western Australia, https://agric.wa.gov.au/n/66


https://grdc.com.au/Media-Centre/Hot-Topics/Preseeding-planning-to-mana…
https://grdc.com.au/Media-Centre/Hot-Topics/Preseeding-planning-to-mana…
https://www.agric.wa.gov.au/frost/science-frost
https://www.agric.wa.gov.au/frost/science-frost
https://agric.wa.gov.au/n/66
mailto:GrowNotes.West%40grdc.com.au?subject=


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Frost will normally affect the smallest pods first, even though they are the higher pods

on the plant. Similarly, pod abortion induced by moisture stress is normally also noted

on the last formed pods in the upper parts of the plant. Visual symptoms of frost and

moisture stress damage to pods are, however, quite different.


In Western Australia, frost or low minimum temperatures (
reproductive stage will not physically damage the crop. There may be a slight leaf

tipping on upper leaves to indicate a frost has occurred.


Frost during early flowering that affects early podset can be compensated for later by

subsequent pods that set higher up the plant, provided the seasonal conditions are

favourable to fill them. 7


Photo 2: Frost can cause flower or pod abortion (usually smaller pods). Damage to

the seed depends on the size of the pod or seed and the severity of the frost.

Photo: W. Hawthorne, Pulse Australia


7 Pulse Breeding Australia (2013) Southern/Western Faba & Broad Bean—Best Management Practices Training Course. Module 2–Plant

Physiology.


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4 ENVIRONMENtAl ISSUES


seCtIon 14 FABA BEANS


WESTERN

NOVEMBER 2017


Photo 3: Frost can cause seed staining from ‘burning’ the seed coat next to

the pod wall.

Photo: W. Hawthorne, Pulse Australia


Tolerance to frost at either vegetative or reproductive stages is not a breeding priority

in southern Australia. However, improved early podset under conditions of low

temperatures and low light is a breeding priority. 8


14.2.1 Managing frost damage

Although it is difficult to totally manage frost risk in pulses, it is important to know

the period of highest probability of frost incidence. Aim to reduce exposure to frost

or impact at vulnerable growth stages. Frost-zone management tactics include

the following.


Use of the frost zone

Map the topography to show areas of greatest risk, and specifically manage these

areas. The use of identified frost zones should be carefully considered. Avoid large-

scale exposure to frost of highly susceptible crops.


Modify soil heat bank

The soil-heat bank is important for reducing the risk of frost. Farming practices

that manipulate the storage and release of heat from the soil-heat bank into the

crop canopy at night are important considerations to reduce the impact of a frost.

These include:


8 Pulse Breeding Australia (2013) Southern/Western Faba & Broad Bean—Best Management Practices Training Course. Module 2–Plant

Physiology.


mailto:GrowNotes.West%40grdc.com.au?subject=


5 ENVIRONMENtAl ISSUES


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NOVEMBER 2017


• Practices that alleviate non-wetting sands, such as clay delving, mouldboard

ploughing or spading.


• Rolling sandy soil and loamy clay soil after seeding.

• Reducing the amount of stubble.


Manipulate flowering times

Sowing time remains a major driver of yield in all crops, with the primary objective

being to achieve a balance between crops flowering after the risk of frost has

passed, but before the onset of heat stress. The loss of yield from sowing late to

avoid frost risk is often outweighed by the gains from sowing on time to reduce heat

and moisture stress in spring. 9


14.3 Waterlogging and flooding


Pulses are generally not well suited to waterlogged soils. Faba beans are the pulse

most tolerant to waterlogging and they exhibit some adaptation in new roots when

the soil has been saturated for >2 weeks. Faba beans are able to produce good

yields under waterlogged conditions that can cause failure of chickpea or lentil crops.


Importantly, the growth of faba beans will still be reduced when they are subjected to

extended periods of waterlogging (>2 weeks), and chocolate spot disease is likely to

be more severe. 10


14.4 Drought


Drought tolerance through osmotic adjustment has not yet been demonstrated in

faba beans, although it is found in many other legumes including chickpeas and

field peas. Deeper root growth, leading to uptake of otherwise unavailable water,

helps the plant to avoid drought by delaying dehydration, but genetic variation and

heritability of the trait are essentially unknown for faba beans. 11


9 GRDC (2016) Tips and Tactics. Managing frost risk: northern southern and western regions, https://grdc.com.au/Resources/

Factsheets/2016/02/Managing-frost-risk-Northern-Southern-and-Western-Regions


10 DAWA (2005) Producing pulses in the northern agricultural region. Bulletin 4656. Department of Agriculture, Western Australia.


11 H R Khan, J G Paull, K H M Siddique and F L Stoddard (2010) Faba bean breeding for drought-affected environments: A

physiological and agronomic perspective. Field Crop Research. 115 (3) 279–286, http://www.sciencedirect.com/science/article/pii/

S037842900900238X


https://grdc.com.au/Resources/Factsheets/2016/02/Managing-frost-risk-No…
https://grdc.com.au/Resources/Factsheets/2016/02/Managing-frost-risk-No…
http://www.sciencedirect.com/science/article/pii/S037842900900238X
http://www.sciencedirect.com/science/article/pii/S037842900900238X
mailto:GrowNotes.West%40grdc.com.au?subject=

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