TEMPERATURE | FROST | WATERLOGGING AND FLOODING | DROUGHT
WESTERN
NOVEMBER 2017
SECTION 14
ENVIRONMENTAL ISSUES
FABA BEAN
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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
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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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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=
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• 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
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