Storing Pulses

Grain Storage chicpea silo

Storing pulses successfully requires a balance between ideal harvest and storage conditions. Harvesting at 14 per cent moisture content captures grain quality and reduces mechanical damage to the seed but requires careful management to avoid deterioration during storage.

KEY POINTS

  • Pulses stored above 12 per cent moisture content require aeration cooling to maintain quality.
  • Meticulous hygiene and aeration cooling are the first lines of defence against pest incursion.
  • Fumigation is the only option available to control pests in stored pulses, which requires a gas-tight, sealable storage.
  • Avoiding mechanical damage to pulse seeds will maintain market quality, seed viability and be less attractive to insect pests.

Quality characteristics

Time-is-Critical

Pulse crops most commonly grown in Australia include broad beans, faba beans, chickpeas, field peas, lentils, lupins, vetch and mungbeans.

Many of the quality characteristics of the grain from these crops are in the appearance, size and physical integrity of the seed. Mechanical seed damage, discolouration, disease, insect damage, split or small seeds will downgrade quality and market value.

Buyers prefer large, consistently-sized seed free of chemical residues for easy processing and marketing to consumers.

Optimum moisture and temperature

Research has shown that harvesting pulses at higher moisture content (up to 14 per cent) reduces field mould, mechanical damage to the seed, splitting and preserves seed viability. The challenge is to maintain this quality during storage as there is an increased risk of deterioration at these moisture levels. As a result, pulses stored above 12 per cent moisture content require aeration cooling to maintain quality.

Grain Trade Australia (GTA) sets a maximum moisture limit of 14 per cent for most pulses but bulk handlers may have receival requirements as low as 12 per cent. As a general rule of thumb, the higher the moisture content, the lower the temperature required to maintain seed quality (see Table 1).

Green pods and grains increase the risk of mould developing during storage — even at lower moisture content. Aeration cooling will help prevent mould and hot spots by creating uniform conditions throughout the grain bulk.

Table 1 maximum recomended storage period

Weather damage hinders storage

Pulses exposed to weathering before harvest deteriorate more quickly in storage. Chickpeas stored for the medium to long term (6–12 months) continue to age and lose quality
(see Table 2). Growers can minimise the effects of seed darkening, declining germination and reduced seed vigour by:

  • Lowering moisture content and temperature
  • Harvesting before weather damages the grain.

Table 2 - storage life of chickpeas

Aeration cooling — vital tool

Aeration cooling:

  • Creates uniform conditions throughout the grain bulk.
  • Prevents moisture migration.
  • Maintains seed viability (germination and vigour).
  • Reduces mould growth.
  • Lengthens (and in some instances stops) insect reproduction cycles.
  •  Slows seed coat darkening and quality loss.

Aeration cooling allows for longer-term storage of low-moisture grain by creating desirable conditions for the grain and undesirable conditions for mould and pests. Unlike aeration drying, aeration cooling can be achieved with air-flow rates of as little as 2–3 litres per second per tonne of grain.

High-moisture grain can also be safely held for a short time with aeration cooling before blending or drying. Run fans continuously to prevent self heating and quality damage.

Be aware that small seeds such  as lentils will reduce the aeration fan capacity as there is less space for air to flow between the grains. For information on aeration cooling management, refer to the GRDC fact sheet, Aeration cooling for pest control.

Damage-control

Aeration drying

Pulses stored for longer than three months at high moisture content  (>14 per cent) will require drying or blending to maintain seed quality. Aeration drying has a lower risk of cracking and damaging pulses, which can occur with hot-air dryers.

Unlike aeration cooling, drying requires high airflow rates of at least 15–25 l/s/t and careful management. For more information on aeration drying refer to the GRDC booklet, Aerating stored grain, cooling or drying for quality control.

Handle with care

In addition to harvesting at high moisture content, growers can manage seeds quality at harvest by:

  • Minimising the number of times augers shift grain.
  • Ensuring augers are full of grain and operated at slow speeds.
  • Checking auger flight clearance — optimum clearance between flight and tube is half the grain size to minimise grain lodging and damage.
  • Operating augers as close as possible to their optimal efficiency — usually an angle of 30 degrees.
  • Using a belt conveyor instead of an auger where possible.

Silos fit the bill

Keep-it-safe-in-silosSilos are the ideal storage option for pulses, especially if they are cone based for easy out-loading with minimal seed damage. For anything more than short-term storage (3 months) aeration cooling and gas-tight sealable storage suitable for fumigation are essential features for best management quality control.

Always fill and empty silos from the centre holes. This is especially important with pulses because most have a high bulk density. Loading or out-loading off-centre will put uneven weight on the structure and cause it to collapse. Avoid storing lentils in silos with horizontally corrugated walls as the grain can run out from the bottom first and collapse the silo as the grain bulk slides down the silo walls.

Pests and control options

Common-insects-of-pulse-grains-

The most common pulse pests are the cowpea weevil (Callosobruchus spp.) and pea weevil (Bruchids pisorum). The cowpea weevil has a short life span of 10–12 days while the pea weevil only breeds one generation per year.

The only control options are phosphine, an alternative fumigant or controlled atmosphere, all of which require a gas-tight, sealable storage to control the insects at all life stages.

For more information refer to the GRDC booklet, Fumigating with phosphine, other fumigants and controlled atmospheres.

Chemical sprays are not registered for pulses in any State. While there is a maximum residue limit (MRL) for dichlorvos on lentils, the product is only registered for use on cereal grains.

Weevil development ceases at temperatures below 20°C. This is a strong incentive for aeration cooling, especially if gas-tight storage is not available.

Keep it clean

Clean-Sweep-Cleaning-MachineryThe first line of defence against grain pests is before the pulses enter storage — meticulous grain hygiene. Because pest control options are limited, it’s critical to remove pests from the storage site before harvest.

Cleaning silos and storages thoroughly and removing spilt and leftover grain removes the feed source and harbour for insect pests.

Clean the following areas thoroughly: 

  • Empty silos and grain storages
  • Augers and conveyers
  • Harvesters
  • Field and chaser bins
  • Spilt grain around grain storages
  • Leftover bags of grain

Chemicals used for structural treatments do not list the specific use before storing pulses on their labels and MRLs in pulses for those products are either extremely low or nil.

Using chemicals even as structural treatments risks exceeding the MRL so is not recommended.

Using diatomaceous earth (DE) as a structural treatment is possible but wash and dry the storage and equipment before using for pulses. This will ensure the DE doesn’t discolour the grain surface.

If unsure, check with the grain buyer before using any product that will come in contact with the stored grain. For more information see the GRDC fact sheet, Hygiene and structural treatments for grain storages.

Vigilant Monitoring Protects Grain Assets

Stored Grain avoid surprises

When grain enters storage it needs monitoring, just as a crop does throughout the growing season.

Regular monitoring means problems are detected early and can be managed before significant grain damage occurs. It also avoids surprises at out-loading, prevents costly rejections from grain buyers and maintains your reputation for supplying quality grain.

KEY POINTS

  • Regular monitoring allows early action to be taken if insects or grain quality issues arise.
  • Failure to monitor grain not only increases the risk of damage and loss but can delay delivery if an issue is first identified at out-loading.
  • Monitor grain temperature and moisture content and check for insect pests.
  • Testing grain retained for seed after harvest helps plan for the following season.

Segregating grain

Monitoring starts at harvest — knowing grain condition and grade as it comes off the paddock determines the appropriate storage conditions.

  • High-moisture grain requires drying or blending.
  • Warm grain requires cooling.
  • Variable quality grain will benefit from segregation.

Avoid surprisesWhen the grade is known (test at a registered receival site) ask what parameter(s) it’s close to for being downgraded or upgraded. It may be something that can be tested for and managed on farm, such as protein, screenings or test weight.

Having this information on hand at harvest can support segregating grain as it comes off helping it to stay within the grade. Alternatively, blending grain from lower-grade areas of the paddock with that from higher grade areas may improve the overall grade.

In some cases, insect pests can come from machinery, so check grain on the way into storage so it can be treated or fumigated. Note: contact pesticides are not an option in Western Australia.

 

Monitor regularly

When in storage, grain is vulnerable to quality loss. Poor management can see grain come out of storage in an unsaleable condition. Monitor grain so problems can be addressed early before they cause significant damage. Dealing with an issue earlier rather than later is easier and more cost effective.

Check stored grain at least once a month during the cooler months and fortnightly during warmer months. Collect samples from the bottom of storage and, if safe, at the top.

In warm conditions (>30ºC) many grain pests can complete their life cycle in as little as 3–4 weeks causing significant damage.

When monitoring stored grain check:

  • For insect pests
  • Grain temperature
  • Grain moisture content
  • Grain quality and germination

 

Sampling stored grain

Probe traps

Collect samples from the areas where insects and mould are most likely to establish first. These areas are generally around openings — hatches, doors, aeration fan inlets, filling and emptying points.

The most common place for insects and mould in a silo is at the top, just below the surface of the peak of grain (see Figure 1). This is because it’s the last place aeration cooling or drying reaches, it’s exposed to the sun heating the headspace, condensation from the headspace and provides easy access for insects through the top lid, inspection hole or vents.

Always follow occupational health and safety guidelines and only climb to the top of a storage if it’s safe to do so.

Always collect samples from beneath the grain surface. At the bottom of a silo this means opening an outlet to run a small amount of grain out. A sampling probe is ideal for collecting grain from the top of a silo, but it’s often impractical or unsafe to climb up a silo with a sampling probe.

Common problem areas in grain stores

Checking for insects

Grain pests can be difficult to find because they are small, fast moving and some prefer the dark while others can be seen on the surface. There are numerous ways to detect them.

Tie the trap to something inside the storage so it doesn’t get lost or forgotten about before out-loading. Position the trap so a small amount is protruding out the top of the grain to capture insects crawling across the surface as well as those hiding beneath.

Temperature

Monitoring grain temperature is not only required to manage aeration, it can indicate potential mould or insect activity in the grain stack.
Insect activity generates heat, which provides favourable conditions for mould. When checking grain temperature, go beneath the surface, measuring in the same spot each time. Record test results to identify any temperature spikes, which will prompt further investigation.

Revealing the pest

Grain moisture

Grain moisture content influences mould and insect activity (see Figure 2). Identifying a change in moisture can reveal an issue before it causes significant damage. For example, an increase in grain moisture at the top of a storage could be a result of a leak, condensation or problem with aeration management.

Seed germination and vigour

EFFECTS OF Temperature and moisture on stored grain

Storing grain at the optimum temperature and moisture content as shown in Figure 2 not only reduces the risk of mould and insects, it maintains grain quality and germination.

CSIRO research reveals how moisture content and temperature affect the rate at which seed germination declines. A trial was carried out with premium quality wheat at 12 per cent moisture content and an initial seed viability of 100 per cent, stored for 150 days.

Storing at 20°C decreased the seed viability by only 1 per cent but storing at 30°C decreased viability by 21 per cent over the 150 days. Reduced germination rates result from a breakdown of grain cellular structure and function, with related changes in chemical composition and modification to enzyme and other bio-chemical systems.

Stored grain deteriorates with time under any conditions, but poor storage conditions (high grain temperature and moisture) accelerate the deterioration process markedly.

Deep temp testing Multimeter temperature test Moisture monitoring

Testing germination rates on retained seed

If retaining grain for seed, a germination test and seed count test performed a month after harvest can help guide how much seed needs to be kept to achieve acceptable paddock plant populations.

If the germination test at this stage is poor, it might pay to buy in seed. If germination is satisfactory, use that to guide how much extra seed to keep, adding an allowance for all the other factors that will reduce germination and seed establishment.

Factors influencing how much seed needs to be retained for sowing include:

  • Germination rate tested at harvest.
  • Further decline in germination between harvest and sowing.
  • Screenings, foreign and small seeds lost at cleaning.
  • Allowance for seeds that germinate but don’t emerge.
  • Seed weight (grams per 1000 seeds).
  • Buffer to allow for change of plans in planting area.

Simple seed germination test

Before sowing, carry out another germination test to check for decline in germination rates during storage.

CSIRO research shows this decline can be around 21 per cent if grain is not stored in ideal conditions.  A decline of more than 10 per cent in germination rate from harvest to sowing should prompt action to improve the storage conditions or management in future years.
Grain temperature has one of the largest influences on seed germination and vigor. Monitor temperature regularly and ensure sound aeration management.