Much of the information in this article is provided by Ken Hellevang, Extension Engineer and Professor with NDSU Extension Service. The information comes from an article he wrote titled “2009 Post-Harvest Tips for Later Maturing Corn”. The full article, plus more information on grain drying, handling and storage is available at http://www.ag.ndsu.nodak.edu/abeng/postharvest.htm .

 

As we move into November, progression to maturity is very slow. The amount of drying in the field depends on factors such as corn maturity, hybrid, moisture content, air temperature, relative humidity, solar radiation and wind speed. Corn in the field may dry about 0.3 to 0.5 percentage points per day during October and decrease to 0.15 to 0.2 per day or less during November. So for example, if corn was at 35% moisture content on October 1 it may dry down to 24% by November 1 and to about 20% by December 1. Of course this timeline will vary depending on the factors listed above. (Note: immature corn dries more slowly in the field than mature corn.)

 

Under normal circumstances, field drying is usually more economical until mid to late October and mechanical high temperature drying is normally more economical after that point.

 

Corn at moisture contents at or above 23% should not be stored in a grain bin because the kernels may freeze together and may deform and bind together. The corn may not flow from the bin for unloading.

 

It is critical to provide aeration to keep the corn cool. Wet corn will deteriorate rapidly unless kept cool. Corn will deteriorate even with airflow, but without airflow through the corn it will increase in temperature resulting in rapid deterioration. Condensation and icing occurs on bin vents at temperatures near or below freezing, so leave bin covers open to serve as a safety opening when operating fans near or below freezing temperature.

 

"Approximate" Allowable Storage Time (Days) for Cereal Grains
	Temperature (0C)
M.C. (%)	-10	40	100	160	210	270
14	*	*	*	*	200	140
15	*	*	*	240	125	701
16	*	*	230	120	70	40
17	*	280	130	75	45	20
18	*	200	90	50	30	15
19	*	140	70	35	20	10
20	*	90	50	25	14	7
22	190	60	30	15	8	3
24	130	40	15	10	6	2
26	90	35	12	8	5	2
28	70	30	10	7	4	2
30	60	25	5	5	3	1

Based on composite of 0.5 percent maximum dry matter loss calculated on the basis of USDA research at Iowa State University; Transactions of ASAE 3330337, 1972; and "Unheated Air Drying," Manitoba Agriculture Agdex 732-1, rev. 1986.

 

* Approximate allowable storage time exceeds 300 days.

 

Corn above 21% moisture should not be dried to safe storage moisture levels using natural air as drying capacity is extremely poor at temperatures below 4 degree Celsius. The same would apply to using low temperature drying to try and reach safe storage moisture levels as this type of drying (and natural air drying) may lead to corn spoilage.

 

If corn is below 21% moisture and storage is the plan before high temperature drying, cool the corn to -6 to -4 degree Celsius for winter storage and start drying in early April. Adding heat doesn't allow for drying of kernels to safe moisture levels but instead reduces the moisture content in storage.

 

In the spring if corn is at low enough moisture contents, natural air drying is the most energy and cost effective method of drying. Corn depth should be limited to about 20 to 22 feet to obtain the desired airflow rate for drying. Turn fans off during extended rain, fog or snow to minimize the amount of moisture moved into the bin by the fan.

 

Using the maximum drying temperature - that will not damage the corn - increases the dryer capacity and can reduce energy consumption. The amount of energy required to remove a pound of water is about 20% less using a drying air temperature of 93ºC than at 66ºC. Be aware that high drying temperatures may result in a lower final test weight and increased breakage susceptibility. In addition, as the drying time increases with high moisture corn, it becomes more susceptible to browning.

 

Housekeeping is critical during drying due to condensation occurring on the dryer creating a wet surface for debris to accumulate. The debris sometimes reduced airflow through the dryer reducing drying capacity and creating a fire hazard.

 

Use in-storage cooling instead of in-dryer cooling to boost capacity of high-temperature dryers. Cooling corn slowly in a bin rather than in the high temperature dryer will also reduce the potential for stress cracks in the kernels.

 

In-storage cooling requires a positive-pressure, airflow rate of about 0.20 cfm/bu or 12 cfm/bu-hr of fill rate. Cooling should be started immediately when corn is placed in the bin from the dryer. Dryer capacity is increased 20 to 40% and about one percentage point of moisture is removed during corn cooling. Condensation problems can be reduced by cooling the corn in the dryer to about 32 degree Celsius before placing it in storage.

 

To help calculate drying costs, refer to MAFRI’s “Crop Drying Cost Calculator” available at the following link: http://www.gov.mb.ca/agriculture/financial/farm/xls/cropdryingcostcalculator.xls

 

Moisture shrink is the reduction in weight as the grain is dried one percentage point. Moisture Shrink Factor = 100  (100 – final moisture content). The shrink factor drying corn to 15.5% is 1.1834. The shrink drying corn from 20.5 to 15.5 would be 5 x 1.1834 = 5.92%.

Normally, corn test weight increases about 0.25 pound for each point of moisture removal during high temperature drying. However, the increase in test weight is affected by the amount of mechanical damage during harvest and the gentleness of the drying. In 2008 in North Dakota, due to the high mechanical damage involved with harvesting 25% to 30% moisture corn and high drying temperatures frequently there was no increase in test weight during drying. There will be little or no increase in test weight on immature or frost-damaged corn.

More fines are produced when corn is wet because more aggressive shelling is required, which causes more kernel cracking and breaking. There is also more potential for stress cracks in kernels during drying, which leads to more breakage potential during handling. In addition, immature corn contains more small and shriveled kernels. Fines cause storage problems because they spoil faster than whole kernels, they have high airflow resistance, and they accumulate in high concentrations under the fill hole unless a spreader or distributor is used. Preferably, the corn should be screen-cleaned before binning to remove fine material, cob pieces, and broken kernels.

 

Corn with damage to the seed coat and immature corn has a shorter storage life than mature corn. Therefore, cooling the grain in storage to about -6 to -4 degree Celsius for winter storage is more important than for mature corn. It is recommended to dry the corn a percentage point lower in moisture content. More frequent checking of the storage is also recommended, and immature or damaged corn is not recommended for long-term storage.

 

Field drying is extremely slow during winter months and corn will only dry to about 20% to 21% moisture content based on the equilibrium moisture content for average monthly air temperature and relative humidity. In North Dakota, corn in the field over winter in 2008-2009 dried from 25% to 30% moisture in November to 17% to 20% when harvested in February and early March.

 

If the stalks stay standing and there isn’t much ear drop, snow cover or wildlife damage, the crop can get through the winter without much yield loss. However, notice the number of disclaimers in that sentence. Ear drop will vary by hybrid and environmental conditions as well as the amount of grain on the ear (smaller ears should stay attached better than larger ears). If winter conditions are cool without snow then corn will continue to dry and can be harvested throughout the winter without too much yield loss. Stalks will become brittle and broken corn parts may decrease the grade causing discounts. Another point to consider is accumulated snow and cover from the corn resulted in wet fields in the spring, possibly delaying spring seeding.

 

If you do find yourself in the position of wanting to over winter your corn, please touch base with your local MASC agent.