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Wheat Coming off "Dry"?

The weather man is bit of a sadist this year. Many areas of the province have so much rain, so frequently, that harvesting wheat has to wait for the fields to get fit. Other areas would sure like some rain as the crops are looking for moisture which is evident by their twisted leaves. Since the harvesting of wheat may be delayed because of field conditions, when the fields do dry up the combines will roll but the wheat may be tough. Waiting even longer for the wheat to dry down might result in sprouting and further quality degradation.

If you are planning to harvest wheat that is tough, you need to have a plan to deal with this wheat quickly. Keeping tough wheat in storage for any length of time is a major quality gamble. The tough wheat can be dried in a heated air drier which we discussed last week in CropPest Issue #11. Natural air can also be used to dry tough wheat but you need to know what you are doing.

Figure 1. This Grain cart is following the combine as it combines wheat.

Natural Air 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. Because of this, the effectiveness of natural air drying systems is greatly reduced during rainy periods, on humid days and at night when humidity levels are normally high. When ambient air temperatures fall below 10oC, the drying process will be slowed considerably and supplemental heat may be required. Natural-air drying during extended periods of humid weather may require some additional heat. Raising the temperature of the incoming air by 5 Centigrade degrees will dry the air, reducing its relative humidity, allowing drying to continue.

Table 1. Recommended Airflow for Natural-Air Wheat Drying

Caution: Just because the fan is running don't assume that it is moving air through the contents of the bin. If the static pressure under the aeration floor exceeds the capability of the fan, the fan is in a stall situation. This means that the fan is spinning, using energy, but it is just churning air. No air will actually be moving up through the grain mass. The only way to know what the fan is doing is to measure the static pressure under the aeration floor and determine the air output from the Fan Performance Curve.

Filling the Bin - Airflow CFM/Bushel

Measure static pressure in the plenum below the aeration floor 90o from the fan position. Use your static pressure gauge as a guide when filling the bin. Operate the fan as you are loading the bin with tough wheat. Stop filling the bin when the fan is delivering 0.75 CFM / bu. airflow, based on the measured static pressure, the fan performance curve and the bushels you have in the bin. This will require just a bit of math but it will be worth the effort when it comes to getting the wheat dry.

Fan Operation for Drying

In general, the fan should only be operated when relative humidity levels fall below 75 to 80% for drying to occur. Do not operate the fan day and night because it will never dry. The Equilibrium Moisture Content of winter wheat at various air temperatures and relative humidity levels can be found in Table 2 below.

Table 2. Equilibrium Moisture Content of Winter Wheat

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 your moisture samples at the same depth each time to know how the moisture content is changing over time, at that depth. Bins with stirrators will have fairly uniform moisture levels throughout the whole bin as a result of the mixing that has been done.