Factors that increase the risk of spoilage for stored canola are high moisture, high temperatures, green seeds and dockage. This article describes these major factors and others.
All canola should be conditioned immediately after combining to cool it down, even out the temperature throughout the bin and remove any moisture released through natural seed respiration that occurs in the first hours to weeks after harvest.
The ideal moisture is eight per cent, but growers should consider moisture and temperature together. For example, eight per cent moisture is still too high if the grain temperature is 25°C or more, 10 per cent is probably low enough if the grain temperature is cooled to 5°C degrees or less.
Moisture creates a more hospitable environment for moulds that trigger heating. Clumping is a sign of mould growth. This can occur fairly quickly. Lab-based research found that canola seeds at 25°C and 10.6 per cent moisture clumped together after 11 days and visible mould colonies appeared after 21 days. With variable conditions in most bins, clumping may occur more quickly in an on-farm situation. Read Questions about handling high-moisture canola.
Canola binned hot, even if it has low moisture, low dockage and low green, should be put on aeration to cool it down. This will even out the temperature throughout the bin, and help remove some of the moisture from respiring seed. Even at low moisture, air movements within the bin could concentrate this moisture. Try to get canola down to below 15°C at harvest time, then turn that fans on again in the early winter to bring it down even lower. Don’t be afraid to freeze a bulk during periods of cold winter weather.
Green canola seeds can increase the storage risk, even if canola is dry and cool. Monitor closely. Small shriveled canola seed, which often comes with high green seed, can mean smaller air pockets between seeds in the bin. Smaller particles will increase the resistance to air flow. This makes it even more important to leave the fan on as it will need to work longer to cool the entire bulk.
Dockage – weed seeds
Weed seeds tend to contain more moisture than canola seeds, especially if they are green or immature. These high-moisture seeds may not be enough to elevate overall grain moisture tests, but if they congregate in pockets in the bin they can create a localized hot spot for spoilage to begin. Bits of green plant material in the sample similarly increase the risk.
Dockage – chaff
Without a spreader in the bin, chaff tends to concentrate closer to the walls of the bin and fines closer to the centre of the bin. This distribution exaggerates airflow problems, with more air taking the path of least resistance up along the walls of the bin and less pushing through the central core. Chaff can also have higher moisture than seed, adding to the risk. That is why concentrated areas of chaff could be a start point for spoilage, even in a bin where the seeds test dry. There is some thought that this risk could be higher with straight-combined canola that could have higher-moisture stalk and pod material.
Dockage – insects
In some years, the canola harvest sample can include a lot of grasshoppers, crickets, cabbage seedpod weevils and even flea beetles. Vincent Hervet, stored product entomologist with Agriculture and Agri-Food Canada, says insect species that come from the field are not a problem with regard to feeding on canola in the bin. However, he says that if the grain has a lot of dead insects coming from the field, the grain should be conditioned (even dried, if necessary) to prevent the development of mould. Hervet adds that canola is not a hospitable environment for most storage insects. Often insects found in canola storage are those that were in the bin prior to loading from previous cereals or other decaying material, but they generally are unable to survive in a canola bin. If bins are treated this fall with malathion to remove any previously existing storage insects, note that those bins cannot be used for canola.
Conditioning and cooling could be more of a challenge in larger bins. Prairie Agricultural Machinery Institute (PAMI) studied air movement through a 25,000-bushel bin. With canola, they found that a standard, single phase 10-hp centrifugal fan could not push air through canola when the bin was full. In fact, the threshold for that bin seemed to be about 17,000 bushels.
Inside-outside temperature differential
Temperature differences result in moisture moving from warmer to colder areas of the bin. During late fall, cold air sinks in the grain at the outside of the bulk, and warm, moister air in the centre of the bulk rises. Condensation may occur when the warm, moister air reaches the cold seeds near the surface. This free moisture and these warm temperatures near the surface can lead to rapid spoilage. In late spring and summer, it is possible to get moisture migration in the opposite direction if the outside temperature is warmer than the seeds (inside the bin). Warming action from the sun on the bin causes air to move up near the outside wall of the bin and down through the centre of the bulk. Moisture is reabsorbed by the cooler canola in the centre of the bin.