Grain Harvesting

Originally written February 1, 2006 | Last updated October 23, 2015

Corn Grain Drydown

By early to mid October, dry-down rates will usually drop to 1/2-3/4% per day (from rates of up to 1% per day in September when drying conditions are usually more favorable). By late October to early November, field dry down rates will usually drop to 1/4-1/2% per day and by mid November, probably 0-1/4% per day. By late November, drying rates will be negligible.ber, probably 0-1/4% per day. By late November, drying rates will be negligible.

Estimating dry down rates can also be considered in terms of Growing Degree units (GDUs). Generally, it takes 30 GDU to lower grain moisture each point from 30% down to 25%. Drying from 25-20% requires about 45 GDUs per point of moisture. In October, we accumulate about 5-10 GDUs per day. However, note that the above estimates are based on generalizations, and it is likely that some hybrids vary from this pattern of drydown.

During a warm, dry fall, grain moisture loss per day ranged from 0.76-0.92%. During a cool, wet fall, grain moisture loss per day ranged from 0.32-0.35%. Grain moisture losses based on GDUs ranged from 24-29 GDUs per percentage point of moisture (i.e., a loss of one percentage point of grain moisture per 24-29 GDUs) under warm dry fall conditions, whereas under cool wet fall conditions, moisture loss ranged from 20-22 GDUs. The number of GUDs associated with grain moisture loss was lower under cool, wet conditions than under warm, dry conditions.

Agronomists generally recommend that harvesting corn for dry grain storage should begin at about 24-25% grain moisture. Allowing corn to field dry below 20% risks yield losses from stalk lodging, ear rots, insect feeding damage and wildlife damage. Be prepared for localized root lodging and stalk lodging that may slow harvest and contribute to yield losses.

Kernel Moisture Ranges (%)

  1. 33-40% Kernel moisture = Silage harvest
  2. 29-32% Kernel moisture = High Moisture Corn (High Moisture Ear Corn and High Moisture Shelled Corn) - ensiled
  3. 25-26% Kernel moisture =  Ideal fo < 20% Kernel moisture =  field losses increase, but cost of drying shell corn is reduced

Assess lodging potential

To assess lodging potential use either the pinch test or the push test to check for stalk integrity. Conduct the pinch test by squeezing the second or third internode above the ground. If it collapses, stalk quality is compromised. The push test is performed by pushing a corn stalk to approximately 45 degree angle. If it breaks, stalk quality has been reduced. If 10 percent of the stalks tested show poor stalk quality or lodge at the root, then these fields should be harvested earlier.

Use your time in combine seat to scout fields

Harvest provides an opportunity to scout your fields. As you travel through the field, you can observe various types of problems that may have occurred during the growing season. Weeds that were not controlled would be one of the most obvious problems that will show up. With the increase in weeds that are resistant to various herbicide classes, it is important to identify these problems as early as possible in order to control them as early as possible to control increases in populations and movement of the weed. This may also provide some opportunity to begin managing the problem this fall.

Insect and disease problems can also be detected in the fall. Note if particular varieties seem more susceptible to an insect or disease. If one variety or hybrid seems to be more susceptible to disease pressure or insect pressure, then this information could be used in variety or hybrid selection for next year. If all hybrids or varieties are affected similarly, then the cause of the problem needs to be identified to aid in selecting management options for next years crop.

Combine settings

Read you operators manual thoroughly.

Combine settings

Read you operators manual thoroughly for detailed settings for you specific combine model. Attend combine clinics to learn fine-tuning methods from other combine operators. With proper adjustment, a quality crop can be harvested.

Corn Harvesting Losses

Pre-harvest Losses

  • Hybrid

    • Ear droppage: One ear (3/4 pound each) in each 1/100 of an acre is equivalent to one bushel per acre. To determine 1/100 of an acre, take the normal 1/1,000 acre distance times ten.  For example, in 30” rows, 1/1000 of an acre is 17’ 5”; 1/100 acre would be that distance across ten rows.  For each ear in that area, there is one bushel per acre loss.

    • Maturity

  • Weather

  • Timeliness

Gathering Losses: grain that does not get into combine

  • Shatter losses caused by the header: count the number of ears and kernels under the header.  Two kernels per square foot are equal to one bushel per acre of loss.  More than a half bushel per acre (or one kernel per square foot average) indicates adjustments would be appropriate.

  • stubble losses

  • stalk losses

  • lodged plants

Machine Losses

  • Improper adjustment of threshing, separating and cleaning sections 

  • Threshing loss is indicated by kernels attached to pieces of cob behind the combine.  These were not shelled by the rotor or cylinder.

  • Separating losses are additional loose kernels on the ground behind the combine.  These were not shaken out of the cobs and husks and were lost over the back of the separator.

How to Measure Losses

  1. Determine average loose kernel loss and cylinder/rotor loss

    • every 2 kernels per square foot = 1 bushel per acre

    • Kernel still attached to cob = cylinder/rotor loss

    • Acceptable level = 1.2 to 3 kernels per square foot

  2. Determine machine ear loss

    • Behind combine, gather all ears on 1/100 acre

    • In front of combine, determine pre-harvest ear loss in standing corn on 1/100 acre

    • Subtract pre-harvest ear loss from ear loss at the rear of machine

    • each 3/4 pound ear = 1 bushel per acre

    • each 1/2 pound ear = 2/3 bushel per acre

    • Acceptable level = 0 to 1.0 bushels per acre

  3. Typical level = 0.6 to 2.5 bushels per acre: Can you limit your total field loss to less than a half bushel per acre?  That would place you and your combine in the top ten percent. 

Test Weight versus Yield

The formula used to determining corn yield is ([100-%moisture] X weight of grain X 109.815 divided by length of row divided by width of harvest swath in inches).

This formula does not consider test weight. Why? Because test weight is not a yield component, it is a volumetric measurement and is not indicative of how much weight in pounds comes off a given area of land. The “weight” in units of pounds is used as the basis for payment of grain. By law a bushel of corn weighs exactly 56 pounds. The weight of grain sold (bushels) is calculated by dividing total weight in pounds by 56 lbs/bushel. No. 1 yellow corn is 56 lbs/bu; No. 2 yellow corn is 54 lbs/bu.

The price a seller receives for grain can be influenced by test weight. For example, grain graders will discount $0.01 per bushel for each lb/bu between 54 and 52 lb/bu; $0.02 per bushel for each below 52 to 50lb/bu and $0.03 per bushel below 50 lbs/bu.

High yielding hybrids can be a high test weight hybrid or a low test weight hybrid. There are a number of factors that influence test weight, genetics, kernel size, density, shape and stickiness. Kernels that are slippery pack better. Wet corn is sticky and does not pack well.

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