Flax TIPS: Late Harvest & Storage
Anastasia Kubinec (MAFRD), Ron Palmer (IHARF), Joy Agnew (PAMI) and Rachel Evans (FCC)
The flax harvest is dragging on. According to Provincial crop reports, as of October 20th; Saskatchewan reported 87% flax harvest and Alberta 81% flax harvest. In Manitoba, Anastasia Kubinec (Oilseed Specialist) estimated 90-95% flax harvest at the time of publication. Harvest conditions have been poor to average, with many cloudy, cool days with high relative humidity. As such, much of the flax may have been harvested tough (10.1-13.5% seed moisture content) and some damp (>13.5% seed moisture content).
Below are recommendations for combining, drying and cooling down late harvested flax.
Late Harvest/ Combining
The concerns with combining flax in late fall are not issues with shelling out or shattering, as flax bolls stay intact (although overripe fields may have boll drop). It is the headaches associated with stalks wrapping on the header reel and high moisture seed being binned and at risk for heating and moulding. Cooler, shorter days in October and November drastically slow stalk/seed drying, so more attention and additional activities may be needed to get the crop off. The following information is based on recent producer calls:
1. Seed is dry, but stalks are green
Even though the seed is at 10% moisture content and ready to harvest, the flax stalks can still be green or have sufficient moisture content to cause the stalks to wrap on the header reel when being straight cut. If this is the situation, consider swathing the crop to kill the stalk. Swathing the crop will allow it to dry down, reducing wrapping problems during combining. Swathed flax may be easier to pick-up later this fall, or next spring if the need arises. If the snow does come sooner than you can get the crop off, its weight may result in significant stalk breakage and/or lodging in flax. Although, the longer the crop is exposed to freeze-thaw conditions, seed quality and appearance will be reduced.
2. Seed is tough or damp
Anything over 10% seed moisture content is considered tough and over 13.5% is damp or high moisture. For long-term storage, flax seed should be brought down to 8.5% moisture. Follow these tips for safe storage of damp or tough flax:
- Aeration fans should be turned on as tough grain is being binned, as this will help to remove moisture as the seed is unloaded. Run the fan as soon as the floor is covered and leave it on until the next morning. It is extremely important to cool the flax immediately, even if the flax is dry. This is done by running the fan all night or whenever the ambient temperature is lower than the grain temperature.
- For tough or damp flax, run the fans from 9 pm to 9 am (unless it is raining or about to rain) until the flax is dry. When the flax has dried down to less than 10%, fans should be run when air temperature is less than flax temperature to keep flax cold. According to Joy Agnew, it may not be possible to actually dry flax when ambient temperature and grain temperature drop below 5oC. Cool and dry grain is ideal for longer term storage, but if it’s not possible to dry, cool grain (<10oC) will help minimize the risk of spoilage.
- Flaxseed generates a large static pressure (or resistance to airflow) for the fan to push against. Ensure your fan type and power can provide enough airflow for effective aeration.
- The larger the perforated floor area, the more effective the air will move through the small sized and densely packed flax.
- Consider removing a truck load to flatten the peak of grain as air may not move up through this area, and instead it will take the path of least resistance up the sides of the bin.
- Temperature and moisture of the binned flax should be monitored closely and potentially daily to ensure moisture content is decreasing.
- With the use of aeration, flax at the bottom of the bin (close to the perforations) will dry faster. When sampling for moisture and temperature, be sure to separately sample the bottom, middle and top of the bin. Be prepared to move the drier flax seed from the bottom to the top of the bin to aid in more uniform drying of the grain.
Natural Aeration of Grain in Late Fall
A common question at this time of year is, “If the air temperature is cooler than the grain, but the humidity is high (say 75%) will the fans still dry the grain?”
According to Ron Palmer (IHARF), warm air holds more water than cool air. Air at 10⁰C and 75% relative humidity is holding 6.8 grams of water per cubic meter. Whereas air at 20⁰C and 75% relative humidity is holding over 13 grams of water per cubic meter. When the 10⁰C air hits warmer grain at 20⁰C; the air immediately warms to 20⁰C without changing the amount of water it is holding, 6.8 grams. The relative humidity of this warmed air is now, 6.8/13 = 52%. This is dry air and very good for drying. In general, grain will dry when grain is being cooled.
However, this effect of “cooling equals drying” may be limited, says Joy Agnew (PAMI). She cautions that once the grain temperature drops below 10⁰C, there will be very little moisture removal from the grain. This is because the mass transfer of water between grain and air is very slow when the temperature is below 10⁰C.
Both experts agree that when natural air drying in the fall, moisture taken out of the flax may form condensation on the roof and walls of the bin which could cause spoilage if the condensation rains down. According to Joy Agnew, the solution is to ensure you have sufficient vent area in the headspace to allow moist air to escape the bin. The rule of thumb is to have one square foot of vent area for every thousand cfm. For example, if you are pushing 1 cfm/bushel through a 4000 bushel bin, you will need 4 ft2 of vent space for efficient ventilation.
Consider the Use of Supplemental Heat
If the flax is cooled down < 5⁰C, the risk of spoilage is minimal even if it is a bit tough. However if one wants to get the moisture content down quicker, or if there is high dockage or if weather is cool and rainy; supplemental heat should be considered. The most effective time to apply supplemental heat is at night, when the air is the driest. Essentially, by warming the ambient air by a few degrees, you are increasing its capacity to hold moisture without adding any moisture.
The flax should be heated for a few hours, and the temperature raised several degrees, and then immediately cooled with the dry night air. Actually it is in the cooling process that the drying occurs. Several smaller episodes of adding heat are more effective than trying to do it all at once. For even faster drying results, especially for damp flax, one might have to consider using batch or continuous air grain dryers (Ron Palmer, IHARF).
Some guidelines to keep in mind when using supplemental heating (Joy Agnew, PAMI):
- Ensure you have sufficient fan capacity (airflow rate) to achieve at least 0.5 cfm/bushel before adding supplemental heat to the fan.
- It’s true that natural gas and propane heaters add water to the air (water is a by-product of the combustion process), but the amount of water added is insignificant compared to the amount of water in the air and in the grain.
- Limit air temperature increase to 10°C or less;
- Higher temp increases results in high fuel costs, reduced efficiency and increased chance of over drying.
- Do not exceed an inlet (after heater) temperature of 20°C.
- Once inlet (after heater) temperature drops below 5°C, very little drying will occur.
- For every temperature increase of 10°C, the RH of the air is effectively cut in half.
- Once average moisture content in the bin is within 0.5 to 1% of target moisture content, turn off heater and blow cool air through the grain to finish drying and cool the grain (target temperature = 10°C or lower).
