Managing Stored Pulses on Farms
EDMONTON - Aug 31/17 - SNS -- Pulse crops retain their quality and maximize their marketability when a few grain storage guidelines are followed. However, pulses can be downgraded if cracked seed coats or split seeds are present in the sample, or if a significant amount of seeds are heated or have a musty odor.
"Monitoring stored pulses begins shortly after harvest with grain spoilage risk increasing if the crop was harvested after wet weather or an early frost," says Neil Whatley, crop specialist, Alberta Ag-Info Centre. "Since pulses are combined at tough or higher seed moisture content to prevent mechanical damage to the seeds, aeration is used to bring the crop down to dry."
Dr. Joy Agnew of the Prairie Agriculture Machinery Institute (PAMI) says that since pulses are harvested early, the weather generally cooperates for effective aeration and natural air drying. As such, additional heat with a supplemental heating system is usually not required.
Dockage Holds Moisture
"Green seeds, dockage and foreign material hold moisture and can also reduce aeration flow," says Whatley. "As such, they should be cleaned out of the sample prior to storage to avoid causing any heating in the bin."
Generally, pulse crop seeds continue to respire or breathe after being harvested, causing the crop to go through a 'sweat' period for the initial six weeks in storage. This sweating can raise the grain temperature and cause moisture to accumulate within the grain mass, producing favorable conditions for mould growth. Using aeration bins is the most effective method to control this situation.
"Whether to use aeration, natural air drying (NAD) without additional heat or a heated air drying system depends on the grain's moisture content," says Whatley. "If the grain is somewhat tough at one to two% moisture content above dry, aeration is usually sufficient. However, if the grain must come down three to four% moisture content, a NAD system removes this extra moisture. While aeration can be completed in a few days, drying can take a couple weeks."
If only aeration is required, PAMI advises producers to turn aeration fans on as soon as the ducts are covered with grain and run them continuously until the average temperature of the grain is at 15 degrees C or less. Although fans can be turned off during rain storms, PAMI also suggests there is very little moisture movement between grain and air at low airflow rates (0.1-0.2 cubic foot per minute (cfm) per bushel) which is the rate associated with aeration.
"Producers who need to dry their grain by three to four% moisture content will require a natural air drying (NAD) system, also referred to as near-ambient drying," says Whatley.
"Ambient air is the air outside the bin that has the capacity to remove moisture from grain. NAD requires a more powerful fan that provides a higher air-flow rate of 1-2 cfm/bushel. For NAD, fans should be run only during the day, when the air has the best capacity to dry, until the grain is about 1% above the safe-to-store moisture content. At that point, continuous night and day air can be used to finish drying the grain down one more moisture content point and cool the grain for safe long-term storage."
Later in the fall, as air temperatures drop, NAD systems lose their effectiveness for drying grain.
"Cool air can only hold a small amount of moisture and moisture movement from grain to air is very slow at temperatures less than 10 degrees C. So, adding supplemental heat to the inlet air of a NAD system increases the air's ability to hold moisture and dry the grain.
"PAMI suggests limiting the air temperature increase to 10 degrees C and to use a Canadian Standards Association certified heating system and not just a homemade system. Supplemental heat can be used when the ambient air temperature is between -5 degrees C and 15 degrees C. The maximum air temperature after the heater should be between 5 degrees C and 25 degrees C.
"The disadvantage of using supplemental heat is that it increases the possibility of over drying the grain, especially at the bottom of the bin. PAMI suggests running fans with a heater until the bin is 'average' dry, mix the grain, and then cool with aeration."
If artificial heat grain drying is required, air temperatures should not exceed 45 degrees C for pea and lentil to prevent seed germination problems and/or to prevent quality losses due to hardening or cracking of seed intended for food use. Additionally, the sample should not be dried more than four to five percentage points per pass through the dryer. For feed pea, dryer temperatures up to 70 degrees C can be applied.
"To get grain into the safe storage zone, it should be brought down to 15 degrees C or lower," says Whatley. "Regularly check the temperature of the grain in the bin. Measure temperature by using permanently installed temperature sensing cables, by probing the grain with an electronic sensor device, or by inserting a metal rod into the bin and checking it for warmth at various points from the tip."
If an aeration system is not available to cool the grain, turning grain outside the bin, or coring, is an alternative to aerating it in the bin when the ambient air temperature falls below 15 degrees C.
"Turn the grain every two to four weeks until the grain temperature reaches 15 degrees C or less," says Whatley.
"This procedure involves removing about one-third of the grain from the bin, allowing it to cool overnight, and then putting it back in the bin. When moving pulse crops, grain augers operated full and at low speeds reduce seed coat cracking and seed splitting. Pulse seeds at 12% moisture content and lower are more susceptible to chipping and peeling when handled.
"Cool, dry storage conditions allow the crop to be stored for a lengthy period, but if seed moisture content or temperature rises, storage time lessens. This table indicates the number of weeks recommended for safe storage of field pea at various grain moisture contents and storage temperatures. Other pulse crops are similar."