ISSUE 15 August 19, 2004
POST-HARVEST TIPS FOR LATE MATURING CORN
Yield potential for corn frozen during the milk stage is low. Ears are difficult to pick and shell, kernel tips may stay on the cobs, and grain will be very chaffy. Therefore, green chopping or ensiling whole plants may be the only reasonable options. Corn silage should be harvested at 60 to 70% moisture. The length of cut should be about 0.5 inch long with not more than 10 to 15% being 1 inch or longer. A bunker or horizontal silo should be crowned in the center, have a wall slope of 1:6 to 1:8, and be covered with 6 mil polyethylene. To be effective the plastic must be held down over its entire area. Temperatures above 120 degrees after 4 days indicates that excess air is getting into the silage.
Test weights will be much less, probably 40 to 45 lb/bu., for corn frozen in the dough stage. Although corn will eventually dry to an acceptable harvest moisture, it will take at least a week longer than mature grain. During the extended drying period, field losses due to stalk breakage and ear dropping will increase. Ear molds will likely develop if warm ambient temperatures follow the frost. The only means of stopping mold growth are drying the grain or ensiling.
Standing corn in the field may dry 0.75 to 1.0 percentage point per day during warm, dry fall days with a breeze. Normally about one-half percent per day is expected in North Dakota. Immature, frosted corn can mold on the stalk.
A hard freeze in the dent stage will result in shriveled kernels with lower test weight.
Shelled corn can be stored in a grain bin at moisture contents up to about 25% if it is kept below 30 degrees using aeration. Shelled corn should be at 25 to 30% moisture for anaerobic (without oxygen) high moisture storage in silos or silo bags. Any tears in the plastic bag must be promptly repaired to minimize storage losses. Whole shelled corn can be stored in oxygen-limiting silos, but a medium grind is needed for proper packing in horizontal or conventional upright silos. Wet grain exerts more pressure on the silo than corn silage, so conventional concrete stave silos may require additional hoops or the silo must not be completely filled.
The desired moisture content for safe cribbing of ear corn is 20% or less. Late in the season when temperatures are consistently near or below freezing, ear corn can be cribbed at moisture contents of 22 to 25%. Crib width of 6 to 9 feet can be used for 20% moisture or less and widths of 4 to 5 feet for 20 to 25% moisture corn. The importance of clean husking cannot be over-emphasized, since the husks greatly reduce airflow through the crib. Locate corncribs away from buildings in a well-drained area oriented with the side facing the prevailing wind.
Dryers will be operated more hours than usual, so examine them carefully and perform needed maintenance before harvest. Use the maximum allowable drying temperature in a high temperature dryer to increase dryer capacity and energy efficiency. Be aware that high drying temperatures result in a lower final test weight and increased breakage susceptibility. Use in-storage cooling instead of in_dryer cooling to reduce fuel use and 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.
As the drying time increases with high moisture corn, it becomes more susceptible to browning. Research indicates that exposure to drying air temperatures above 200 degrees for time periods in excess of 2 hours will likely result in some degree of browning. For corn above 30% moisture, browning is likely to occur. Dryer temperatures may need to be limited to less than 160 degrees to prevent scorching or browning.
In-storage cooling requires a positive-pressure, aeration, 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.
Dryeration will increase the dryer capacity about 50 to 75% and remove about 2 to 2.5 points of moisture. (0.25% for each 10 degrees the corn is cooled.) With dryeration, hot corn from the dryer is placed in a dryeration bin with a perforated floor, allowed to steep for 4 to 6 hours without airflow, cooled, and then moved to a storage bin. There will be a tremendous amount of condensation during the steeping and cooling process, so the corn must be moved to a different bin for storage or spoilage will occur along the bin wall and on the top grain surface.
Combination drying greatly increases the drying capacity of a high temperature dryer, saves gas, and improves corn quality. Combination drying is the process of using a high temperature dryer to dry the corn to about 20 to 22% moisture, placing the corn hot in a natural air drying bin, and then completing drying with an airflow rate of at least 1.0 cfm/bu.
Natural air and low temperature drying should be completed as much as possible in October because the drying capacity is extremely poor during the colder temperatures in November. Corn above 21% moisture should not be dried using natural air and low temperature drying to minimize corn spoilage during drying. An airflow rate of 1.25 cfm/bu is recommended to reduce drying time. Adding heat does not permit drying wetter corn and only slightly increases drying speed. The primary effect of adding heat is to reduce the corn moisture content.
Energy cost for high temperature drying corn will be about $0.016 per bushel per point of moisture removed using $0.70 per gallon propane, $0.020 for $0.90 propane, $0.025 for $1.10 propane and $0.029 for $1.30 propane. Total drying cost includes capital and fixed costs such as depreciation, repairs, insurance, and etc. This cost will vary depending on dryer cost and the amount of grain dried. This might be $0.10 to $0.15 per bushel. It costs about $8.00 for energy to remove 5 percentage points of moisture from 100 bushels of corn using $0.70 propane. This is equivalent to a field loss of 3.5 bushels if corn is $2.25 per bushel.
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%.
Moisture meters will not provide accurate readings on corn coming from a high temperature dryer. The error will vary depending on the amount of moisture removed and the drying temperature, but the meter reading may be about 2% lower than true moisture. Check the moisture of a sample, place the sample in a closed container for about 12 hours, and then check the moisture content again to determine the amount of error. Moisture meter errors increase as corn moisture contents increase, so readings above 25% should only be considered estimates.
A few wet loads can lead to spoilage in storage or in natural air & low temperature drying bins. Measure the moisture of every load going into and out of a dryer and into storage.
Normally, corn test weight increases about 0.25 pound for each point of moisture removal during high temperature drying. However, there will be little 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.
Immature corn has a shorter storage life than mature corn. Therefore, cooling the grain in storage to about 20 to 25 degrees for winter storage is more important than for mature corn. More frequent checking of the storage is recommended, and immature corn is not recommended for long-term storage. Corn kernels above about 25% moisture may freeze into a clump that causes unloading problems.
Extension Engineer & Professor
Ag & Biosystems Engineering Department