Corn Production Guide (continued)

A-1130, May 1997

Corn Harvesting

Every bushel of corn left in the field represents a loss in profit. Combine losses cannot be reduced to zero, but skillful operators usually can reduce losses to an acceptable level without affecting the rate of harvest.

Corn is mature when the grain has about 30 to 32% moisture. The best time to harvest depends upon the individual's harvest and storage system. Early harvest has several advantages:

• Less lodging from stalk rot and severe storms.
• Less chance of water logged fields which delay or prevent harvest.
• Less ear droppage.
• Less grain is shelled when the ears hit the snapping rolls.

The following chart shows the relationship between field losses and delayed harvesting:

Averages from tests in Illinois, Indiana, Iowa, and Nebraska over several seasons.

The drawback to early harvest is that it can require more energy for drying. But, the extra corn saved can often more than cover the cost.

To keep harvesting losses low, you need to know where losses occur, how to measure them, what reasonable loss levels are, and what machine adjustments and operating practices will reduce losses.

Where Losses Occur

Preharvest losses are ears that drop from the stalk before harvesting begins. These losses are not caused by the combine, but they can be reduced by harvesting early.

Corn harvest losses can be separated into four types. Gathering losses occur at the front of the combine and consist of ears missed or dropped by the machine and loose kernels shelled by the snapping rolls in the cornhead. Cylinder and separating losses will be found on the ground behind the combine. Cylinder losses are kernels attached to pieces of cob that were not shelled by the combine cylinder. Separating losses are loose kernels that were not shaken out of the cobs and husks and were lost out the rear of the combine.

How to Measure Losses

Ear losses can be measured from an area equal to 1/100 acre. Each 3/4-pound ear (or its equivalent in smaller ears) found in this area is approximately equal to a loss of 1 bushel per acre. The length of row for 1/100 acre depends on your row width and the number of rows being harvested. (See Table 1.)

The easiest way to measure loose kernel losses is to use a rectangular frame enclosing 10 square feet. Every 20 kernels of corn found within the frame is approximately equal to 1 bushel per acre loss. Make the frame out of heavy wire or 1/8 inch rod. The width of the frame should be the same width as your corn rows. The length of the frame is listed in table 2.

To measure losses, stop your combine a few rows in from the edge of the field. Disengage the header, raise the header, and back up 15 to 20 feet. Measure off an area of 1/100 acre on the harvested rows behind your combine, gather all missed ears of corn within this area, and count the number of equivalent �-pound ears to determine total ear loss.

If total ear loss is high, mark off an area of 1/100 acre in the standing corn in front of the combine, gather all missed ears, and count the number of equivalent �-pound ears to determine preharvest loss. Subtract preharvest loss from the total ear loss to find machine ear loss.

To measure kernel losses, place the rectangular frame over the first harvested row behind the combine. Remove the stalks, husks, and leaves, and count the kernels attached to pieces of cob and the loose kernels within the frame. Record each count separately. Then move the frame over onto the next row and count the kernels. After kernels are counted from all the rows being harvested, divide the total number of kernels attached to cobs by the number of rows, and then divide the answer by 20 to find cylinder loss. Divide the total number of loose kernels by the number of rows, and then divide the answer by 20 to find the total loose kernel loss. This will be the sum of snapping roll shelling and separating loss.

Next, place the frame over the first harvested row in front of the combine header. Be sure to measure between the standing corn and the residue dropped from the rear of the combine. Remove the stalks and leaves, count all loose kernels within the frame, and divide by 20 to find snapping roll shelling loss for that row. Move the frame over and count the kernels in the next row. Record the count for each row separately, because only one row on the cornhead may be out of adjustment and may be shelling more corn than the others. After counting losses for all rows, add them and divide by the number of rows to find an average snapping roll loss. Subtract this average loss from the total loose kernel loss found behind the combine to determine separating loss.

What are reasonable loss levels?

Iowa extension personnel checked 84 central Iowa corn combines, and the average loss for the top 10% and average operators are listed in Table 3. Machine ear loss and snapping roll shelling were the most frequent causes of high field losses. Harvest losses were lowest when kernel moisture was between 19 and 23 percent. Losses increased as lodging increased and were the highest in weedy fields.

If your losses are greater than the average values in Table 3, stop and find out why. Your goal should be to reduce your losses to the levels shown for the top 10 percent of the combines in the survey.

Adjustments and Operating Practices to Keep Losses Low

Keep your combine in good repair. Keep chains properly adjusted and belts tight. Lubricate bearings and roller chains when they're warm to get better lubricant penetration.

Properly governed engine speed is essential for proper separator action. The recommended speed for the engine and the cylinder is in your operator's manual. Check these speeds when the engine is at operating temperature.

Adjust snapping roll speed and spacing to snap ears about one-half to two-thirds of the way up the snapping bars. Snapping bars should be spaced narrower in front than in back to prevent wedging. A spacing of 1-1/4 inches in front and 1-3/8 inches at the back will be satisfactory under most conditions. If a wider spacing is used, small ears will wedge between the snapping bars and shelling losses will increase. Be sure snapping roll spacing and snapping bar spacing are the same on all rows.

Adjust gathering chains so the flights are opposite each other and extend about 1/4 inch beyond the snapping bars.

Gathering snouts should just touch the ground under normal field conditions. If corn is badly lodged, slow down and let the snouts float on the ground. Under good field conditions, maintain a field speed of 2.5 to 3 miles per hour. If separating losses are high, slow down.

Adjust cylinder-concave clearance according to your operator's manual and adjust cylinder speed to fit corn conditions. For conventional combines with transverse cylinders, clearance is usually 7/8 to 1� inches in front and 1/2 to 7/8 inch at rear. It is best to adjust cylinder or rotor speed to recommendations as listed in your operator's manual. This is due to the wide range of cylinder and rotor diameters. Diameters range from 17 to 30 inches. Cylinder bar travel speed in feet per minute is similar for all combines whether conventional cylinder or rotary type. Excess cylinder speeds often cause severe crop damage. If cob breakage is severe, increase the rear cylinder-concave spacing 1/8 inch and then increase cylinder speed to improve shelling.

Corn Drying and Storage

Corn must be harvested at moisture contents above that acceptable for storage to increase harvest efficiency, minimize harvest losses, minimize damage to the corn kernels, and due to uncertain weather conditions.

There are many acceptable methods of drying corn. Each has its advantages and limitations, so each situation must be evaluated to select an appropriate method.

In-bin dryers can be grouped as natural air, low temperature, and high temperature. Natural air drying is economical and there is no "bottle-neck" at harvest, since bins are filled at the harvest rate. Corn at 21% moisture content can be dried to 15% in about 36 days during October using an airflow rate of 1.25 cfm/bu. Because the temperature is about 20� cooler in November, the drying time increases to about 70 days and the final corn moisture content will be about 18%.

Low temperature drying is defined as a natural air system with the air heated 5-10�F which permits drying during periods of higher humidity and slightly reduces drying time. Adding enough heat in October to warm the air by 5� will reduce the drying time a little, but will also dry the corn to about 14%. Warming the air by 5� during an average November permits drying the corn to 15% in about 52 days using an airflow rate of 1.25 cfm/bu. Warming the air by 10� in November would further reduce the final moisture content and slightly reduce the drying time.

Layer drying using a natural air or low temperature (NA/LT) system permits harvesting limited amounts of grain at higher moisture contents than could be dried in a full bin.

Fans warm the air that passes through them. The amount the air is warmed depends on operating static pressure, fan type, and fan efficiency. Temperature increases of 2-4�F have been measured at 4 inches of static pressure and 4-6�F at 6 inches of static pressure. This temperature increase needs to be included in designing and managing a NA/LT drying system.

Airflow moving from bottom to top of a bin is recommended for NA/LT drying, so the last grain to be dried is at the top of the bin where it can be monitored and for ease in determining when the grain is dry. NA/LT drying fans should operate during the night to provide the most corn drying hours. The decision to stop natural air drying fans during wet weather needs to be made after evaluating the grain allowable storage time, expected drying period, and corn equilibrium moisture content for a 24 to 48 hour period.

There is no single best fan for all applications. The fan selected must deliver the most airflow at the expected operating static pressure. Vane-axial fans will typically deliver the most airflow at low static pressures. Low speed centrifugal fans will generally deliver the most airflow at moderate static pressures. In-line centrifugal fans will deliver the most airflow at moderate to high static pressures. High speed centrifugal fans deliver the most airflow at high static pressures.

Combination drying utilizes a high temperature dryer to remove some of the moisture, then uses a NA/LT dryer to complete the drying. This increase the high temperature drying capacity by two to three times and results in high quality grain.

High temperature bin drying permits efficiently drying higher moisture content grain in a bin faster and under conditions that would not be possible with a NA/LT drying system. High temperature bin batch dryers are simple, but it is difficult to determine the appropriate time to stop drying so the overdried grain on the bottom of the bin mixes with the wet grain at the top to achieve the desired average moisture content after the bin has been unloaded. Stirring devices are recommended to mix the grain during drying to achieve a uniform moisture content when the drying air is heated more than 10�. A high temperature continuous flow bin dryer removes dry grain from the bottom of the bin as it reaches the desired moisture content. It is an efficient dryer, but the disadvantage is that the hottest air contacts the driest grain, which can damage grain quality if excessive temperatures are used.

High temperature column dryers are categorized by the drying process as batch, recirculating batch, automatic batch, and continuous flow. The batch dryer sequences through fill, dry, cool and unload. In a continuous flow dryer these steps occur simultaneously. High temperature dryers are also categorized by the airflow pattern in the dryer as cross-flow, counter-flow, concurrent-flow, and mixed flow. The cross-flow dryer is the most common type.

Germination rates drop rapidly as kernel temperatures exceed 120�F. Therefore, maximum recommended drying air temperature is 110�F for seed. Maximum recommended drying air temperature for commercial corn in the various types of dryers are: continuous flow and recirculating batch, 200�; column batch, 180�, and bin batch 120�. Corn kernel temperature should not exceed 140� on corn for wet milling. There is normally about a 40� difference between plenum air temperature and average kernel temperature in a cross-flow dryer. Therefore, a 180� plenum temperature should be an acceptable maximum recommended temperature for drying corn for wet milling. Remember that corn moisture and temperature varies across a high temperature drying column.

High temperature drying is effective during periods of high humidity and cold temperatures. Air that has a very high relative humidity will have a very low relative humidity after it has been heated. Air that is 40� and 90% relative humidity will have a relative humidity of only 1% after being heated to 180�. The energy required to heat air to 180� from -20� will be 1.4 times greater than heating it from 40�. The amount of energy required to heat the air can be calculated using the formula: Btu/hr=cfm x 1.1 x temperature increase. Partial air recirculation should be considered on corn dryers to reduce energy costs.

Dryeration is the process of allowing hot grain from a high temperature dryer to steep in a bin without airflow for about six hours, followed by cooling which removes about 0.25 percentage point of moisture for each 10�F the grain is cooled. Grain must be moved to a storage bin to mix grain wet by condensation next to the bin wall on the top during steeping with dry grain. Dryeration increases the drying rate about 60%, increases energy efficiency, and reduces kernel stress cracks.

Cooling grain in the bin increases drying rate about 30 percent. An airflow rate of 12 cfm/bu-hr cools the grain at the fill rate and is required to rapidly cool the grain to minimize condensation near the bin wall.

Grain moisture content needs to be measured accurately for proper drying and storage. Since moisture content varies, it is important that the sample measured is truly representative of the whole. Most moisture meters are influenced more by kernel surface moisture than internal moisture. If moisture is not uniform through the kernel, the sample should be placed in a plastic bag or other moisture tight container for about 12 hours prior to measuring the moisture content. Kernel temperature affects the measured value. An adjustment should be made manually or automatically to the measured moisture content to adjust for temperature. It is best to estimate the amount of error in measuring the moisture content of corn coming from a high temperature dryer by measuring the measure content, placing the sample in a sealed plastic bag for 12 hours, then checking the moisture content again. Growing conditions affect the composition of grain and therefore its moisture measurement. Measurements can vary by almost a percentage point for differing growing conditions. The moisture content of numerous samples should be taken to assure the most accuracy in measurement.

Grain storage management requires monitoring the grain including probing, checking the temperature and moisture content at various locations within the storage, using insect traps and screens. The grain should be checked every two weeks until a storage history is developed and the grain has been cooled for winter storage. The grain should be checked at least monthly during the winter. Keep records of the grain condition each time the grain is checked.

Grain stores best when it is cool and dry. Optimum conditions for both insect activity and mold growth is at about 80�F. Insects are dormant at temperatures below about 50�F and are killed at temperatures below freezing. Grain should be cooled to about 25�F for winter storage.

Previous recommendations indicated that grain should be warmed in the spring. Since grain stores better at lower temperatures, current recommendations are to aerate to create a uniform grain temperature of about 40�F for summer storage. Moisture migration during the spring and summer causes a moisture content increase of 0.5 to 1.0 percentage point about 2-3 ft below the top center grain surface. Warming the grain to summer temperatures would increase the moisture content of all the grain by 0.5 to 1.0 percentage point.

The amount of dockage varies within a truck load and across the grain stream from the end-gate of a truck. Therefore, the sampling method must collect grain from the entire grain stream to truly represent a cross-section of the grain in the truck. Samples should not be collected from the first or last portion of a load because this is not a true cross-section of the load. The grain must be handled so its condition does not change. For example, the grain should be placed in a sealed container to prevent the moisture content from changing prior to measuring the moisture content.

Resource Publications

North Dakota State University:

• Fertilizing Corn Grain and Silage (SF-722)
• Agricultural Weed Control Guide (current year) (W-253)
• Field Crop Fungicide Guide (current year) (PP-622)
• North Dakota Hybrid Corn Performance Testing (current year) (A-793)
• European Corn Borer Development and Management (NCR 327)
• Uneven Emergence in Corn (NCR 344)
• Herbicide Symptoms in Corn (NCR 94)
• White Grub Management (E-901)
• Corn Insects in North Dakota (E-631)
• Silage Production and Management (R-846)
• Grain Drying (AE-701)
• Crop Storage Management (AE-791)
• Crop Dryeration and In-Storage Cooling (AE-808)
• Energy Conservation and Alternative Energy Sources for Corn Drying (NCH-14)
• Grain Moisture Content Effects and Management (AE905)
• Calculating Grain Drying Cost (AE923)
• Maintaining Corn Quality for Wet Milling (AE119)
• Natural Air & Low Temperature Crop Drying (EB35)

University of Minnesota

• Corn Growth and Development & Management Information for Replant Decisions (FO-5700)
• Corn Insects-Above Ground (MI-0569)
• Corn Insects-Below Ground (MI-3289)
• European Corn Borer Development and Management (BU-2322)
• Fertilizer Management for Corn Planted in Ridge-Till or No-Till Systems (FO-6074)
• Fertilizing Corn in Minnesota (FO-3790)
• Managing Nitrogen for Corn Production on Irrigated Sandy Soils (FO-2392)
• Natural-Air Corn Drying in the Upper Midwest (BU-6577)
• Setting Realistic Crop Yield Goals (FS-3873)
• Soil Nitrogen Test Option for N Recommendations With Corn, A (FO-6514)
• Some Important Insect Larvae Affecting Corn (FS-0581)
• Understanding Nitrogen in Soils (FO-3770)
• Cultural and Chemical Weed Control in Field Crops (BU-3157)

South Dakota State University

• Gerwing, J. and R. Gelderman. 1996. EC750 — Fertilizer Recommendations Guide SDSU/CES.
• Hall, R.G. C253-1996 South Dakota Corn Performance Trials, SDSU/AES.
• McLeod, M.J. Insecticide Recommendations for South Dakota Corn and Sorghum, 1997. SDCES FS 888 CD.
• McLeod, M.J. 1996. Economic Thresholds for First Generation Corn Borers. SDCES EXEX 8125.
• McLeod, M.J. 1992. First generation European corn borer management. SDCES EXEX 8079.
• McLeod, M.J. 1992. Second generation European corn borer management. SDCES EXEX 8080.
• McLeod, M.J. 1992. Scouting adult corn rootworms. SDCES EXEX 8082.
• Wrage, L. Weed Control in Corn, FS 525C.

Corn Resource Contacts

North Dakota State University

Duane R. Berglund, Agronomist 701-231-8135
Marcelo Carena, Agronomist/Breeder 701-231-8138
Phil Glogoza, Entomologist 701-231-7581
Marcia McMullen, Plant Pathologist 701-231-7627
David Franzen, Soils Science 701-231-8884
Ken Hellevang, Agric. Engineering, Drying & Storage 701-231-7243
Vern Hofman, Agric. Engineering, Machinery 701-231-7240
Richard Zollinger, Weed Science 701-231-8157

University of Minnesota

Jeffrey L. Gunsolus, Weed Science 612-625-8130
Dale R. Hicks, Agronomist 612-625-1796
John Moncrief, Soils/Tillage 612-625-2771
George Rehm, Soil Fertility 612-625-6210
Bill Wilke, Agric. Engineering 612-625-8205
Ken Ostlie, Entomology 612-624-9272
Ward Stienstra, Plant Pathology 612-625-6290

South Dakota State University

Robert G. Hall, Agronomist 605-688-4760
Jim R. Gertwing, Soils 605-688-4772
Murdick McLeod, Entomology 605-688-4601
Marty Draper, Plant Pathology 605-688-5157
Leon J. Wrage, Weeds 605-688-4591

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A-1130, May 1997