Weather is finally allowing for some harvest to resume across the Prairies, but the concern now is how to handle canola that could come off very tough, or damp.
Make a drying, storage or marketing plan prior to taking it off the field, as even at low temperatures the bulk will likely be quite volatile. Spoilage can occur rapidly.
These steps will help improve conditioning results and reduce risk:
1. If possible, under-fill available bin space. The less depth to aerate, the better, because it is possible that spoilage could occur before the aeration front even reaches the peak of the bin.
2. Keep aeration fans on. Even if the air doesn’t have capacity to dry at this point, aerate to cool and create uniform temperature conditions in the bin.
3. Use supplemental heat, if possible. Air that is less than 10°C has very limited drying potential. Adding heat to cool air will increase its water holding capacity, and therefore capacity to dry. (See below for more points on this.)
4. Turn the bulk frequently. Turning the bulk can break up potential hot spots that have started to form, and will also help to even out the conditions in the bin. This also provides a chance for additional inspection.
5. Monitor diligently.
Use of supplemental heat
Adding heat to cold air will greatly increase that air’s capacity to dry, even if the relative humidity (RH) of the cool air is high. Here are some key tips for that process:
1. Air needs to be heated to more than 10°C to have good drying potential.
2. Only heat the air up to 15-20°C. With relatively low air-flow rates of aeration systems, it is important to only use warm air, not hot, to avoid “baking” seeds closest to the fan.
3. Airflow of at least 0.75 cubic feet per minute per bushel is recommended for natural air drying with supplemental heat. (See below for more on how to estimate your fan’s airflow.)
4. To estimate the required heater capacity for supplemental heating, multiply the desired temperature rise in degrees Fahrenheit by the air-flow rate provided by the fan in cfm. Then multiply by 0.8. The result will be the heater capacity in btu/hr. For example, for a target temperature rise of 10°C (18°F) and an airflow of 5,000 cfm, the required heater capacity is 18 x 5,000 x 0.8 = 72,000 btu/hr.
Although it is potentially possible to stabilize a bulk if the temperature is uniformly dropped to less than 5°C, drying canola now is better than waiting. Otherwise the bin will be unstable as soon as temperatures warm up, whether next spring or sometime this fall, and will need to be dried immediately. More: Tips for drying tough and damp canola
What if you have a plan for drying, but it means holding onto the grain in the meantime? The graph below is often referenced when trying to determine the number of “safe days” producers have before spoilage begins. Be very cautious using these charts. This work was performed in small tubes, where the temperature and moisture conditions were uniform. Realistically, conditions are never totally uniform in a bin, and this is what precipitates the spoilage process.
These charts should only act as a very rough guide. Assume much fewer safe days in the “real world.”
How to estimate airflow rate (cfm/bu) through a bin
The airflow rate from the fan depends on the fan type (axial, centrifugal, etc.), fan size (hp) and the resistance to airflow (grain type, grain depth, type of ducting, etc.)
If the fan already has a static pressure gauge, read the pressure (usually given in inches of water) when the fan is running and the bin is full (or is holding the amount of grain you want to condition or dry). Then find the fan curve chart for the make/model/size of the fan. Most fan manufacturers list these specs online. An example chart for low-speed centrifugal Chief fans is below. The last digits in the model number indicate the fan size in hp.
Using this sample table, if the static pressure (or resistance to airflow) the fan is pushing against is 6″ of water and you have a 5 hp fan, the airflow rate will be 3,700 cubic feet per minute (cfm). Then divide that number by the number of bushels in the bin to estimate the cfm/bu airflow rate.
If you don’t have a pressure gauge (after-market gauges can be installed), estimate the resistance to airflow based on grain depth using the graph below. Joy Agnew from PAMI has a video that explains in more detail why airflow matters and how to use this graph.