NDSU Extension - Ramsey County


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September 27 Agriculture Column


How about that rain???  The weather man predicted a half inch of rain for us and the southern parts of North Dakota to get hammered, but somehow he was off a little.  My gauge read 2.55 inches with many area reports from 2-2.5 inches.  There were amounts higher and lower but that seems to be the norm for the county.  The upper basin coulees are running at spring levels in many cases.  Of course we still have a lot of harvest left with 20-30% of the canola and wheat left to harvest.  The most of this crop is northeastern part of the county with a line drawn from Cando to Doyon.  There is also other areas but this area has been the most affected by wet conditions.  We are also starting to see some browning of dry edible beans, within the pod.  This will likely put them at a very severe discount or even rejected.   Another problem arises from the wet conditions.  We do have farmers that cannot get to their crops for harvest and others that have gotten to the crop but decided it might easier to pile the grain in the field and move after conditions are froze.  Hopefully this week will allow a large portion of harvest to be completed and get us ready for bean and edible bean harvest with corn not far behind.  Growing degree days has improved  to 2100 GDD’s in the southern half of the county and around 1950 GDD’s in the northern half of the county.

Natural air drying crops during a wet late harvest

 Warming the air when natural-air drying primarily changes the final grain moisture content, but only slightly increases drying speed. Airflow rate determines the drying speed. Appropriately selecting the amount and timing of supplemental heat is critical to efficiently dry wheat during a late fall. Shutting fans off at night is not recommended due to drying times become excessively long.


Even for conditions that may occur in the northern part of the state in late September to early October, the air only needs to be warmed about 7 degrees to reduce the relative humidity from 70 percent at 50 degrees to the desired 57 percent at 57 degrees to dry the wheat to 13.5 percent moisture. Since the air is warmed about 4 degrees by the fan operating at about six inches of static pressure, only an additional 3 degrees needs to be provided by a supplemental heater. A rule of thumb on wheat is that 1 kW of heat per horsepower of fan motor will warm the air about 5 degrees. Therefore, only about a 3 kW heater is needed for a five horsepower fan to provide the desired amount of heat.


Without supplemental heat, the final wheat moisture content may be about 14.0 to 14.5 percent during October drying depending on weather conditions. Average October weather conditions are 44 degrees and 69 percent relative humidity at Devils Lake and 46   degrees and 64 percent relative humidity at Williston.


Only running the fan during the warmer and drier portion of the day will lengthen the drying time. The estimated drying time is about 50 days to dry wheat from 17 percent to 13.5 percent using an airflow rate of 0.75 cfm per bushel with an air temperature of 50 degrees and 55 percent relative humidity. It will take 100 days to dry the wheat if the fan is operated just during the warmer 12-hour period of the day.


Drying time will be longer at cooler temperatures because the cooler air cannot hold as much moisture. It takes about 27 days to dry wheat from 17 percent to 12.2 percent with an average August air temperature of 69 degrees and an airflow rate of 0.75 cfm per bushel. It will take about 32 days to dry wheat from 17 percent to 13 percent with an average September temperature of 58 degrees and the same airflow rate. 


The drying rate is directly proportional to the airflow rate. If it takes 21 days to dry to 16 percent moisture using an airflow rate of 1 cfm per bushel, it will take 28 days with an airflow rate of 0.75 cfm per bushel and 42 days at 0.50 cfm per bushel. The airflow rate must be increased to increase the drying speed. Adding heat to a bin will cause the wheat to be dried to a lower moisture content, but decrease the drying time very little.


Shut off the fans during foggy, rainy or snowy weather if it lasts for more than a few hours. Wheat at 15 percent to 16 percent moisture can be without airflow for a few days, but wheat at 18 percent moisture should not be without airflow for more than a day or two due to the potential for heating and spoilage.


If drying is not completed in the fall, wheat can be cooled to about 25 degrees for winter storage and drying completed in the spring.


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