Optimizing Combine Adjustments

Operator manuals contain the best starting point for setting up a small grain harvester. Occasionally conditions arise that require further adjustments. Harvest of fusarium-damaged grain, lodged crops or crops infected with dwarf or common bunt requires special attention. The easiest and best way to improve the grain sample in these situations is with proper combine adjustment. Often the difference between a marketable crop and sample grade wheat is in the combine set-up. Don’t be afraid to experiment.

Storage of the crop allows the opportunity to upgrade the grain before delivery to an elevator or mill. This is particularly important for wheat infested with any of the bunt diseases. Many producers have experimented with re-cleaning the grain through screen cleaners, seed cleaners and fanning mills to upgrade the crop to a better sample. Elevator operators can also do this, for a fee. This can have tremendous economic benefit, where grain can be moved from salvage grade to milling grade. Upgrading the grain makes it much easier for the elevator to handle the crop and find a purchaser for the grain.

Fusarium-Damaged Grain

Combines use air blast to separate grain from the chaff in a normal harvest operation. Many of the Fusarium-infected kernels are small, shrunken and lighter than sound kernels. It is often possible to blow a large proportion of these Fusarium-damaged kernels out the back of the combine by increasing the air blast above normal ranges. In 1996, many producers operated combines at the maximum windblast to increase grade. Research conducted by Dr. A Schaafsma (University of Guelph, Ridgetown Campus) in 1996 found a tenfold decrease in Fusarium-damaged kernels in the grain when fan speeds were operated at maximum blast (up to 300 rpm above book settings). Operating cleaning fans at these levels causes an additional loss of good kernels, up to 0.13 t/ha (2 bu/acre) Refer to Table 4–25, Effect of different fan-speeds on wheat yield. This small yield reduction is insignificant if the crop can be made marketable, rather than being downgraded to feed, sample or salvage.

Table 4-25. Effect of different fan-speeds on wheat yield

Harvest fusarium damaged grain as quickly as possible. Fusarium levels can increase dramatically when harvest is delayed. Fusarium can continue to grow whenever grain moisture exceeds 19%, which occurs frequently in wheat any time there is precipitation.  However, moistures above 16% reduce the ability to blow out lighter Fusarium damaged kernels. Early harvest, and harvesting at lower moisture, often work against each other. Slowing the forward ground speed of the combine may further reduce Fusarium levels. This allows increased separation of the grain mass, giving the increased windblast time to separate the good kernels from the infected kernels. Consider adjusting the cleaning sieves (chaffer) to a more wide-open setting. This directs the air blast vertically, slowing rearward movement of the grain mass and aiding cleaning and separation. Use caution to keep heads and straw particles out of the grain sample if the chaffer is opened.

Unfortunately, there will be times that the grain cannot be raised to milling standards. If this occurs, consider storing as much of the damaged grain as possible. Often, as harvest finishes, the pressure eases on those involved in handling the crop. Marketers and millers are able to assess the markets that do exist and determine the best way to condition wheat to fit that market.

Wheat going into storage must be dry (14% moisture or below). Damp wheat allows the Fusarium to continue to grow and produce toxins, further downgrading the crop. Check stored grain frequently to ensure that the grain stays in condition.

Lodged Grain Crops

Setting up a combine for lodged wheat takes extra time and care while in the field. Although flexible cutter bars on floating soybean heads are standard on modern combines, there are several effective options for harvesting lodged grain crops.

• Grain Lifters lift the crop above the cutter bar and is an inexpensive way to maximize yields.
• Knife Adjustment: On floating cutter bars, leave the knife tilted down and run the header in the float position, similar to harvesting a soybean crop. Take care not to feed rocks into the combine if choosing this option.
• Reel Adjustment:  Most reels are permanently on the best setting for soybean harvest. Newer combines have hydraulic adjustments from the cab, but this setting is not appropriate for a lodged cereal crop. Set the reel forward and adjust the tine angle to be more aggressive, allowing the reel to physically lift the crop up off the ground and above the knife. Check the operator’s manual for suggested settings and fine-tune from there.
• Harvesting Direction: The last option, some years, is to harvest the grain in one direction so the lodged grain is tilted towards the header rather than away.

Bunt-Infected Wheat

To avoid being forced into harvesting a bunt-infected crop, use resistant varieties of properly treated seed. However, when bunt does infect the crop, harvest and storage must focus on minimizing bunt balls in the sample and reducing the “fishy” odour following harvest.

Do not harvest bunt-infected crops at high moisture. Spores from broken bunt balls adhere more easily to damp grain. Harvest dry grain using slow cylinder speeds and open concave clearance to minimize the number of bunt balls broken during the harvest process. Operate cleaning fans at high speed to blow as many of the bunt balls and bunt spores out the back of the combine as possible.

Storage of bunt-infected wheat is an effective way to upgrade the grain. Aeration is the key. Store bunt-infected grain in storage facilities with lots of aeration capability. Aerate the grain until the odour has disappeared. Take care when removing the grain from storage, as the handling process can break remaining intact bunt balls and re-contaminate the grain. Belt conveyors are preferable to augers when moving bunt-infected grain. Use of aspiration during the handling process will often lift out remaining bunt balls and keep the grain in condition.

Never contaminate or attempt to blend bunt-infected wheat with clean wheat. It takes very little bunt to downgrade the grain. Blending will simply contaminate the good grain, not improve the damaged grain. For more information, refer to Dwarf Bunt and Common Bunt.

Drying and Storage

Winter wheat is sometimes harvested at higher moisture contents because of impending wet weather or to reduce harvest losses. Wheat is considered dry at 14.5% moisture by the Canadian Grain Commission (CGC), however the Ontario industry moved to 14% to align more closely to other world standards.  Drying charges could be implemented to wheat at greater than 14% moisture.

Winter wheat must be dried to 13%–14% moisture content for safe, long-term storage.

Drying Systems

Three different systems can be used to dry wheat:

• natural-air drying bin
• low-temperature dryers (less than 40°C)
• high-temperature or high-speed dryers (temperatures greater than 40°C)

Natural-Air and Low-Temperature Drying

Natural air drying of wheat will only occur when the relative humidity of the outside air is below the equilibrium moisture content of the grain. The effectiveness of natural air-drying systems is greatly reduced during rainy periods and at night when temperatures are cool and relative humidity levels are normally high. When air temperatures fall below 10°C, forced ambient air will not pick up as much moisture, and supplemental heat may be required. Extended periods of humid weather may also require additional heat to affect drying. Raising the temperature of the incoming air by 5°C will dry the air but should not over-dry the grain at the bottom of the bin. Refer to Table 4–26, Suggested airflow for natural-air and low-temperature wheat drying, for airflow rate guidelines for natural-air and low-temperature wheat drying.

Table 4-26. Suggested airflow for natural-air and low-temperature wheat drying

Minimum requirements for natural-air drying:

• full aeration floor in the bin
• level grain surface across the entire bin
• minimum airflow of 6.5 L/sec/m³ (0.5 CFM/bu), preferably 9.7 L/sec/m³ (0.75 CFM/bu) or more
• clean wheat with no weed seeds or fines
• accurate moisture determination of the wheat in the bin
• accurate outside air temperature and relative humidity measurement
• an understanding of wheat equilibrium moisture content
• on/off switch for the fan

A full aeration floor is essential to move air uniformly through the entire bin contents. With a partial aeration floor or air duct system, dead areas will exist, leading to potential spoilage problems. Weed seeds, green trash and fines accumulations in the bin will restrict or divert airflow. Air moving through the wheat mass will take the path of least resistance.

High-Temperature Drying

With high-temperature drying, large volumes of heated air, 40°C or higher, are used to accomplish drying in a few hours or days. Corn dryers could be used but it may be necessary to reduce the drying temperature to avoid loss of starch quality and germination. It is important not to exceed the recommended maximum air temperatures for drying milling wheat which are dependent on the type of dryer used and the end use of the wheat, refer to Table 4–27, Guidelines for maximum air temperatures for drying milling and seed wheat.

Table 4-27. Guidelines for maximum air temperatures for drying milling and seed wheat

The baking quality of wheat is reduced if the temperature of the grain reaches 60°C for any significant length of time. When heated air dryers are used, it is a worthwhile precaution to have samples evaluated to ensure the dried grain meets market standards.

Tough wheat can be dried with natural air under good drying conditions. Natural-air drying of wheat requires careful management by the operator since wheat loses and takes on moisture easily. Only run the fan when outside conditions will result in drying progress.

Determining Airflow

Sufficient airflow is needed to move drying air through the entire wheat mass. To remove moisture, the minimum airflow required is 6.5 L/sec/m³ (0.5 CFM/bu); anything less will only change the temperature but not the moisture content of the wheat. Higher airflow rates of 9.75 L/sec/m³ (0.75 CFM/bu) or greater help speed up the drying process. These higher airflow rates may be difficult to achieve, requiring much higher fan horsepower. The small kernel size of wheat causes the spaces between the kernels to be small. Moving large amounts of air through deep beds of wheat will take a large fan with high static pressure capability. If this bin and fan combination is capable of supplying 26 L/sec/m³ (2 CFM/bu) when filled with corn, only fill it one-half to one-third that depth with wheat. With axial flow fans, filling the bin with wheat to one-third the depth of corn is a good starting point.

To determine the L/sec/m³ (CFM/bu) value for a bin, determine the number of bushels in the bin and the static pressure that the fan is operating against. A simple manometer connected to the air plenum below the perforated floor will show the static pressure (inches of water displaced in the column). Refer to Figure 12–1, Home-built manometer for a diagram of a homemade manometer. Determine the fan output at the measured static pressure using the fan performance curve.

If adequate airflow cannot be achieved, one strategy is to partially fill the bin. In this way, the fan will be operating at less static pressure and will deliver higher airflow rates per bushel.

Equilibrium Moisture Content

Researchers have developed equilibrium moisture content tables, that allow the prediction of the final moisture content of winter wheat when exposed to air with a certain temperature and relative humidity, refer to Table 4–28, Equilibrium moisture content for soft winter wheat exposed to air.

Table 4-28. Equilibrium moisture content for soft winter wheat exposed to air

For example, you can find the equilibrium moisture content of wheat exposed to outside air at 25°C and 80% relative humidity. In Table 4–27 find the point at which the 25°C row and the 80% relative humidity column intersect. This point will be the equilibrium moisture content for wheat at the outside air conditions stated. Given enough time, the wheat will dry down to 14.4% moisture content.

When to Run the Fan

Air temperature and relative humidity levels should determine fan operation, not the time of day. On some days, drying can be accomplished from 9 a.m. until midnight, while on others it may only be from 9 a.m. to 6 p.m. Check the temperature and relative humidity of the air frequently throughout the day. As the wheat loses moisture, drier outside air is needed to continue to make drying progress. If the equilibrium moisture content on a given day is less than the moisture content of the wettest wheat, drying is possible and the fan should be on. Install a humidistat that will activate the fan at preset humidity levels. The operator can adjust the relative humidity level at which the fan is activated.

The wheat at the top of the bin will be the last to dry. Each day of fan operation will push a drying front up through the bin. This drying front may not reach the top of the bin that same day. Be sure to take moisture samples at the same depth each time to know how the moisture content is changing at that depth. Bins with stirrators will have fairly uniform moisture levels throughout the entire bin as a result of the mixing that has been done.