Corn & Soybeans Harvest Management
Harvest Management Tips for Corn and Soybeans
Every grower is anxious to get started with harvest and fill grain trucks and bins. However, managing harvest requires some attention to detail, including field monitoring, planning and combine adjustment.
Delayed Harvest Management
Managing for Delayed Corn Crop Development
- Corn development and maturity may be delayed in seasons with late planting and/or cool summer temperatures.
- Freezing temperatures occurring before normal crop maturity (i.e., prior to kernel “black layer” development) may reduce corn yields.
- The impact on corn yield from an early freeze depends on the stage of corn growth, low temperature reached, duration of the low temperature period, and other factors.
- Corn leaf tissue can be killed by a few hours near 32 F, and in even less time at temperatures below 32 F.
- Temperatures below 32 F for several hours would likely kill all the leaves and may stop ear development.
- When grain is wet at harvest or impacted by an early, killing freeze, quality may be reduced. Subsequent harvest, handling, drying and storage of this grain requires extra care to prevent further quality reductions.
- Cylinder/rotor speed and concave clearance are the combine adjustments most critical to reduce grain damage and threshing losses with wet/immature grain.
- Drying temperatures need to be limited on corn of 25% to 30% moisture content or higher to avoid scorching grain and causing stress cracks that increase kernel breakage.
- Follow optimum grain storage procedures to minimize quality issues with wet or immature grain.
- Screen grain. “Core” bin and level grain mass after filling.
- Maintain aeration until grain mass equilibrates.
- Monitor grain in storage by checking every 2 weeks.
Corn maturity may be delayed by late planting and/or below normal summer temperatures. When slow corn development continues into the fall, corn grain may be significantly wetter at harvest. This can result in higher drying costs, mechanical damage to grain, and if a killing frost occurs before corn reaches maturity, yield reductions. This article discusses the possible impacts of cool temperatures and an early freeze on corn development, grain yield, field drydown, harvest, artificial drying and storage.
Effect of Planting Delays
Because growing degree unit (GDU) accumulation in early to mid-May is similar to GDU accumulation in late September when corn is maturing, each day of planting delay could result in a commensurate 1-day delay in maturity. However, corn is able to adjust to late planting by reducing its total GDU requirement slightly, by about 5 GDUs for each day planting is delayed beyond May 1. This means that corn maturity is usually delayed by only about 1 day for each 1.5 days of planting delay.
Effect of Cool Summer Temperatures
“Cool” or “moderate” summer temperatures are rarely more than 1 or 2 degrees below normal when considering the entire summer period. Such conditions would result in a deficit of 90 to 180 GDUs that has to be made up in late summer/early fall. This would result in about a 1- to 2-week delay in corn maturity in the central Corn Belt, and up to 3 weeks in northern corn-growing areas.
Corn Maturity Development
During the ear-fill stage of corn development, kernels progressively gain in “dry weight” as starch accumulates and displaces moisture in the kernel. Beginning at the “dent” stage (R5), a line of demarcation is visible between the hard, structural starch deposited in the crown of the kernel, and the milky content of the rest of the kernel (toward the tip). This border is known as the “milk line” (Figure 1).
Figure 1. Progression of milk line in corn kernels from R5, or early dent (left) to R6, or physiological maturity (right).
Corn physiological maturity is complete when an abscission layer (“black layer”) forms at the tip of the kernel, halting further nutrient transport into the kernel and marking the end of yield accumulation (Figure 2).
Figure 2. Progression of black layer development in corn kernels (at tip of kernels), indicating physiological maturity (R6).
As corn reaches the R6 stage, moisture content of the kernel is at about 30% to 35%. At this point, grain quality can still be reduced due to combining, drying and handling of wet grain, but the crop is no longer at risk of yield loss due to frost.
Yield Reduction Caused by an Early Freeze
The impact on corn yield from an early freeze is dependent on stage of corn growth, low temperature reached, duration of the low temperature period, and other factors (Lauer, 2004). A freeze event with temperatures below 32 F for several hours would likely kill all the leaves and may stop ear development entirely. Should this occur, growers need to determine the ear development stage at the time of the freeze to estimate percent yield loss (Table 1 and Figure 3).
Table 1. Potential corn grain yield losses after frost.
Derived from Afuakwa and Crookston (1984)
Corn leaf tissue can be killed by a few hours near 32 F, and in even less time at temperatures below 32 F. At temperatures between 32 to 40 F, the extent of damage may vary considerably, depending on microclimate effects, the aspect of the field slope, and whether or not atmospheric conditions favor a radiation frost. In such cases, it is possible that only upper leaves in the canopy would be killed, while leaves lower in the canopy survive and remain photosynthetically active. If the leaf tissue is killed, it will be evident in 1 to 2 days as a water-soaked appearance, which will eventually turn brown. Therefore, it is best to wait 5 to 7 days before making an assessment of percentage leaf damage for purposes of estimating yield reduction.
Figure 3. Kernel growth stages and approximate grain moisture, GDUs to maturity (black layer or "no milk line"), and yield loss from a hard, killing frost that stops kernel development.
Corn Kernel Drydown
The period from black layer to harvest is defined as the "drydown" period. Kernel moisture loss during the drydown period is entirely due to evaporative moisture loss affected by air temperature, relative humidity and wind. When corn reaches maturity late in the season, field drydown is slower due to cooler air temperatures. For example, according to Ohio State University Extension, corn drying rates of 1% per day in September will usually drop to 1/2% to 3/4% by early to mid-October, 1/4% to 1/2% per day by late October to early November, and only 1/4% or less by mid-November (Thomison, 2011).
DuPont Pioneer research indicates that it takes approximately 15 to 20 GDUs to lower grain moisture each point from 30% down to 25%, 20 to 25 GDUs per point of drydown from 25% to 22%, and 25 to 30 GDUs per point from 22% to 20% (DuPont Pioneer, unpublished). If a hard freeze occurs that stops corn development prior to maturity, these field drying rates may be affected. For example, corn frosted as early as the dough stage may require 4 to 9 extra days to reach the same harvest moisture as corn not frosted (Maier and Parsons, 1996).
Grain moisture at harvest affects the time and cost required to dry the grain to acceptable storage moisture levels, as well as grain quality. Wet grain can incur damage during combining, handling and drying. If grain quality is significantly reduced during harvest and drying, allowable storage time is also reduced, dockage may result, and losses of fines and broken kernels can trim bushels of saleable grain.
In seasons with delayed corn crop development, many growers will have to deal with wetter than normal grain at harvest. Several steps can be taken prior to harvest to make this job go more smoothly (Lauer 2009).
- If you have recorded silking dates by field, use these notes to predict the order in which fields will reach black layer and harvestable moisture. This will help in setting up a harvest schedule. However, be sure to base the schedule on crop condition as well as grain moisture, taking into account stalk quality and insect or disease damage.
- Where such options exist locally, consider harvesting (or selling) more of your crop as silage or high moisture corn.
- Explore locking in a price for the additional fuel needed for grain drying. Compare the fuel costs vs. possible dockage for shrink if wet corn is delivered to the elevator.
- Consider some field drying if grain moisture levels are high, but don’t wait too long! Wet field conditions can keep combines out of the field as crops deteriorate, and snow and ice may increase harvest losses due to ear droppage and stalk breakage.
Harvest Management of Wet / Immature Grain
Combine Adjustments: Grain above 30% moisture can be difficult to remove from the cob and is easily cracked and damaged by overthreshing in the cylinder or rotor of the combine. Cylinder/rotor speed and concave clearance are the adjustments most critical to reduce grain damage and threshing losses. At high grain moisture growers may have to strike a balance between damaged grain and higher than normal grain loss from unshelled cobs.
With very wet grain, some ag engineers suggest beginning harvest with combine settings that would likely underthresh a typical, lower moisture crop (Brook and Harrigan, 1997):
- Set cylinder/rotor speed near the low end of the suggested range.
- Set concave clearance near the widest recommended setting.
- Open the chaffer and sieve to the maximum recommended openings.
- Check with the combine manufacturer for machine-specific recommendations. (Combine mechanics or other dealership staff are often a good source for this information).
- Begin with above settings but check immediately and readjust as necessary to achieve best results. Continue to check and readjust as crop conditions change.
Drying Wet / Immature Grain
Properly drying very wet, lower quality corn is essential to avoid further quality reductions. Growers should screen lower quality grain prior to drying, using a rotary screen, gravity screen or perforated auger housing section. This will help prevent foreign material and broken kernel fragments (or "fines") from blocking air flow essential to uniform grain drying and storage. Next, growers should plan to dry lower quality grain 1 or 2 points lower than the normal 14% to 15% often recommended for long-term storage. This is because of greater variations of moisture content within the grain mass and increased physical kernel damage and broken cobs, which could magnify mold problems.
According to extension specialists at North Dakota State University, energy efficiency is increased at maximum temperatures in high temperature drying systems, but these temperatures could scorch very wet or immature kernels. In addition, high temperature drying causes stress cracks in the kernel, which allows more breakage during handling and storage. The amount of stress cracking depends on initial grain moisture, rate of moisture removal, maximum grain temperature reached in the dryer, and rate of grain cooling. Therefore, drying temperatures need to be limited on corn of 25% to 30% moisture content (or higher).
With natural-air or low-temperature drying systems it will be difficult to adequately dry corn wetter than 26% grain moisture. The maximum moisture content for natural air drying of corn is 21% using an airflow rate of at least 1 cubic foot per minute per bushel of corn (Hellevang, 2009).
The University of Wisconsin gives these additional grain drying tips (Lauer, 2009):
- Fine-tune your dryer so that over- or underdrying does not occur. Overheating the grain in the dryer or filling the bin too fast for drying to occur will increase costs and decrease grain quality, thus reducing profitability.
- Hire and train the skilled labor that will be required to monitor dryers, fans, augers, and other equipment during the drying process.
To reduce drying time and speed harvest, some growers have discussed partially drying and aerating corn while holding it for further drying after completion of harvest. This strategy requires skill and intensive management, especially with low-quality grain. For more tips on grain drying to maximize grain quality, see Appendix I.
Storing Wet / Immature Grain
Low test weight, lower quality grain is harder to store because it is breakage-prone and subject to mold and "hot spot" occurrence in the bin. Because the storage life of this grain may be only half that of normal corn at the same moisture content, consider selling this grain early rather than storing long term.
To minimize storage problems, begin by screen-cleaning grain before binning to remove as much of the fine material, cob pieces and broken kernels as possible. After filling, "core" the bin (remove up to 10% of the total bin capacity) to eliminate broken kernels and fines that accumulate in the center. Next, level the grain in the bin to minimize moisture accumulation at the top of the grain. Finally, cool grain as soon as it is dry to within 10 degrees of air temperature, and continue to aerate for 10 to 14 days to ensure grain moisture "equilibrium" has been achieved.
When growers have fields of wet or immature corn in October, deciding when to start combining is difficult. Experiences during several late harvest years suggest that excessive delays may not be a good idea, for these reasons:
- Delaying starting may also delay finishing at a reasonable date. Most growers require about 6 weeks to harvest the entire crop in a normal year, and another 2 weeks to complete fertilization and tillage. This means growers must start the first week of October to finish before December.
- Drying corn with ambient temperature in the 20s requires more energy than drying corn with ambient temperatures in the 40s.
- Harvesting in the winter limits fall tillage and fertilization, reducing options for crop rotation the following spring.
- Finally, there are safety concerns and potential for increased damage to machinery when harvesting on frozen soils and driving on snow or ice-covered roads.
For these reasons, timely harvest is usually advantageous, even though drying costs may be increased.
Written by Steve Butzen, Agronomy Information Consultant, DuPont Pioneer, Johnston, Iowa.
Afuakwa, J.J. and R.K. Crookston. 1984. Using the kernel milk line to visually monitor grain maturity in maize. Crop Sci. 24:687-691.
Brook, R. and T. Harrigan, 1997. Harvesting and handling high moisture, frost-damaged grain. Harvest Alert Fact Sheet #5. Field Crops Team, Michigan State University.
Hellevang, K. 2009. NDSU Extension Service to provide corn drying information at Big Iron. North Dakota State University Extension Service News Release.
Lauer, J. 2004. Guidelines for handling corn damaged by frost prior to grain maturity. In Issues in Agriculture. University of Wisconsin Extension.
Lauer, J. 2009. Will corn mature in 2009? Agronomy Advice - Field Crops 28:491-70. University of Wisconsin Extension.
Maier, D. and Parsons, S. 1996. Harvesting, drying, and storing frost-damaged corn and soybeans. Grain Quality Task Force Fact Sheet #27. Purdue University.
Thomison, P. 2011. Corn drydown: what to expect? Crop Observation and Recommendation Newsletter 2011:34. Ohio State University Extension.
Appendix l - Optimal Management Practices for Drying and Storage
(John Gnadke, AGS, Inc.)
Continuous Flow Grain Dryers¹
¹To maintain high capacity and grain quality, keep your grain dryer clean!
²Temperature ranges must be within 15 - 20 F anywhere within your plenum.
- In-Bin with stirring equipment - for best results, the operating temperature should be
- In-Bin with low temp heaters (LP or electric) should be operated on a Humidity Controller. This will condition the ambient air to the proper relative humidity (RH). For best results, the RH setting is approximately 70%.
Natural Air In-Bin
- Fan Size: 1.5 CFM of air per bushel.
- Clean grain to 2% or less BCFM.
- Wet grain moisture: 20% for best results.
- Roof Venting: 1.5 sq. ft. per fan HP.
In-Bin Continuous Flow
- Clean Grain to 2% or less BCFM.
- Operating Temp: 130-160 F.
- Keep grain depth from 4 to 6 feet for highest capacity of this unit.
- Proper roof vent is a must (1.5 sq. ft. per fan HP).
- Grain discharge temp will be 95-115 F.
- If stress fractures are a part of a grain contract, take special steps to prevent this from occurring (grain temp: 95-105 F).
- If wet grain is 20% or less, steep for 12 hours before cooling.
- If wet grain is 22-24%, steep for 18-24 hours before cooling.
- If ambient air temps fall below 40 F at night, then DO NOT operate cooling fans.
- Operating cooling fans at 40 F or above will reduce stress on grain (may require day-time operation of these cooling bins.)
Cooling Grain to Proper Storage Temperatures
- Cool grain to 35 F (DO NOT freeze food corn as it can cause additional stress on the grain.)
- Freezing grain at 18-20% moisture can cause ice crystals to form on the kernels.
- When temperature rises in February or March, ice crystals will melt and cause grain to go out of condition very quickly.
- All stored grain should be checked every 2 weeks!
Appendix ll - Grain Storage Principles
(John Gnadke, AGS, Inc.)
- Dry grain to the “equilibrium” moisture level (15%).
- Use LOW temperature drying to minimize stress cracks.
- For ideal grain storage, target 2% cracked/broken.
- Level the grain in the bin to minimize moisture accumulation at the top of the bin (core or use a mechanical “spreader”).
- “Core” the bin by removing 10% of the total bin capacity after filling to remove fines that accumulate in the center. In the coring process try to keep the bin as level as possible.
- Cool grain as soon as it is dry to within 10 degrees of air temperature.
- Aerate the grain for 10 to 14 days after filling to ensure grain “equilibrium” has been achieved – based on 1/4 CFM.
- Monitor grain temperature and moisture regularly (minimum every 2 weeks, preferably on a continuous basis with “in-bin” probes and visual inspection).
- Monitor grain for insect and rodent infestation on a regular basis (minimum every 2 weeks).
- Keep cooling grain on a regular basis until grain temp reaches 35 F. Never cool grain below 32 F.
- Check grain regularly (minimum every 2 weeks) while in storage. 1) Lock out power. 2) Climb into the bin, look, feel, smell, and walk on the surface. 3) If automated controls are used, biweekly inspections are still recommended to ensure controls are functioning properly.
- Aerate on a regular basis while in storage, discontinue fan run-time when temperatures fall below 32 F.
Managing Delayed or Frost-Damaged Soybeans
Soybean maturity is determined primarily by daylength, but planting date affects soybean maturity as well. Agronomists estimate that soybean maturity can be delayed by about 1 day for every 4 days of planting delay beyond the normal date. Growing conditions such as abnormally cool summer temperatures can also affect soybean growth, development and maturity. When crop maturity is delayed, the risk of damage due to a fall frost increases, especially in northern states where the full growing season is commonly used. This article discusses managing delayed soybeans and those damaged by a freeze prior to crop maturity.
Freeze Damage to Soybeans
Soybean plant tissue is more tolerant of freezing temperatures than that of some other crops such as corn. However, temperatures below 32 F can damage leaves, and temperatures below 30 F for an extended period can damage stems, pods and seeds. The severity of damage depends on the growth stage of the soybeans, the low temperature reached and the duration of the freezing temperatures.
Oftentimes, a first fall frost is light and limited in duration. Such a frost is most likely to damage only the leaves in the upper canopy of the plant. In such cases, soybean pods and seeds can continue to develop, and yield may be only minimally affected. However, a more severe freeze that damages stems, pods and seeds has the potential to reduce both the yield and quality of the crop.
Soybean Reproductive Growth Stages
Soybean researchers have divided soybean reproductive development into 8 stages — 2 each for flowering, pod development, seed development and maturity. Because flowering, pod development and early seed development occur in July and August, soybeans are rarely exposed to a frost at these stages. However, soybeans are exposed to potential frost damage at the full seed and maturity stages in a late-planted season and/or one with cool summer temperatures, especially in northern states. Should a frost occur before maturity, growers need to determine the soybean growth stage at the time of the freeze to estimate potential yield loss (Table 1)
and Figure 1).
Table 1. Description of soybean growth stages R6 to R8.
R6 – Full Seed Stage
Seed moisture: ~ 75% - 80%.
~25 days remaining until full maturity.
Yield loss ~ 20% to 35%.
R6.5 – Midway from Full Seed to Maturity
Seed moisture: ~ 65% - 70%.
~16 - 18 days remaining until full maturity.
Yield loss ~ 10% to 15%.
R7 – Beginning Maturity Stage
Seed moisture: ~ 55% - 60%.
~8 - 10 days remaining until full maturity.
Yield loss ~ 0% to 5%.
R8 – Full Maturity Stage
Seed moisture: ~ 25% - 35%.
Yield loss ~ 0%.
Figure 1. Soybean growth stages and approximate seed moisture, days to
maturity and yield loss from a hard, killing frost that stops seed development.
Assessing Soybean Damage
Frost damage within a soybean field may vary considerably, depending on microclimate effects, landscape position in the field, canopy density, and other factors. Generally, thick plant canopies formed by narrow rows and/or high plant populations tend to hold the soil heat better and protect the lower portion of the plants and pods to some extent. After a frost, it is best to wait 2 or more days before making a crop assessment, to allow damage to be fully expressed.
If only a light frost occurs, damage may be confined to the upper leaves in the canopy. After a waiting period, damaged leaves will appear wilted and dried, but usually remain on the plant. Undamaged leaves (likely lower in the canopy or in higher landscape positions in the field) should still appear green and healthy. Some maturity delay (several days) may be expected on damaged plants, and small pods near the top of the plant may abort or fail to fill normally.
If a more severe freeze occurs, leaves in the lower canopy may also be damaged, as well as stems and pods. Frost-damaged stems turn dark green to brown. Beans that were still green and soft at the time of the freeze will shrivel, reducing soybean yield (seed size and test weight), quality and drying rate. If beans had reached physiological maturity (R7) prior to the freeze, these yellow beans should dry normally, and quality should not be affected.
Soybeans are graded by USDA standards to determine the quantity of damaged seeds (e.g., heat damaged), splits, foreign material, and off-color beans (e.g., green), and loads with a musty or sour odor. With delayed maturity or frosted soybeans, loads could be discounted for most or all of the above criteria. For that reason, care must be taken in harvest, handling, drying and storing of this year's crop.
Harvesting / Drying Freeze-Damaged Soybeans
If soybeans have been frosted prior to maturity or have higher than normal moisture at harvest, combine settings may have to be adjusted to minimize harvest losses. Reduce the concave clearance and then begin to increase rotor or cylinder speed if more aggressive threshing is needed for wet, tough soybeans. Check behind the combine and readjust settings as conditions change throughout the day or season.
Soybeans should be at 16% seed moisture or below for ideal threshing, but with delayed maturity or early frost, some fields may be wetter than this late in the season. In those cases, harvesting at 18% or slightly higher moistures can be attempted if soybeans are sufficiently defoliated, but drying is required. Dryer temperatures need to be significantly lower for soybeans than for corn, as too much heat causes excessive seed coat cracking and eventual splits. Keeping the relative humidity of the drying air above 40% minimizes cracking, but this greatly limits dryer temperature and may not allow the through-put needed. Find more information on soybean drying.
Storing Freeze-Damaged Soybeans
A normal soybean crop should be dried to 13% for a 6-month storage period, and 12% for 12 months of storage. For lower quality soybeans, experts suggest drying grain 1 or 2 points below that required for a normal crop, monitoring grain closely while in storage (at least twice monthly), and storing this grain for only 6 months rather than a year.
Green soybeans may be the primary concern of growers with this year's crop. Studies have shown that green soybeans, if properly dried, have the same storage properties as normal soybeans. However, preliminary studies have also shown that green beans do not lose their internal green color, although the surface color may lighten or mottle somewhat after weeks or months in storage. For this reason, growers may want to screen grain prior to storage to remove smaller green beans, to help avoid significant discounts at the elevator.
Berglund, D. Assessing frost damage in soybeans. North Dakota State University.
Maier, D. and Parsons, S. 1996. Harvesting, drying, and storing frost-damaged corn and soybeans. Grain Quality Task Force Fact Sheet #27. Purdue University.
Monitor Corn Fields for Stalk Quality Problems
Crop Insights written by Steve Butzen, Agronomy Information Manager
Reducing Harvest Losses Due to Stalk Lodging
Careful scouting and harvesting fields according to crop condition can help prevent field losses due to low stalk quality. Corn loss potential should be weighed just as heavily as grain moisture in deciding which fields to harvest first. Scouting fields approximately 2 to 3 weeks prior to the expected harvest date can identify fields with weak stalks predisposed to lodging. Fields with high-lodging potential should be slated for early harvest.
Weak stalks can be detected by pinching the stalk at the first or second elongated internode above the ground. If the stalk collapses, advanced stages of stalk rot are indicated. Another technique is to push the plant sideways about 8 to 12 inches at ear level. If the stalk crimps near the base or fails to return to the vertical position, stalk rot is indicated. Check 20 plants in 5 areas of the field. If more than 10% to 15% of the stalks are rotted, that field should be considered for early harvest.
Collapsed corn stalk.
- Stalk lodging problems occur on some corn acres every year in North America, due to a variety of stresses that affect stalk quality.
- Drought, low sunlight, insect and disease pressure, and low fertility are major stresses that reduce the photosynthetic rate or leaf area of the corn plant.
- If photosynthesis is unable to supply the demands of the developing kernels, the plant redirects root and stalk carbohydrates to the ear. Stalk rot organisms can then invade weakened and dying plant tissues.
- Careful scouting and harvesting fields according to crop condition can help prevent field losses due to low stalk quality.
- This Crop Insights explains the causes of stalk rot problems in corn, and how to prevent stalk problems from reducing harvestable yield.
Many different stresses to the corn plant can lower stalk quality, with the result that stalk problems occur in some fields each year throughout the major corn-growing areas of North America. Drought stress, reduced sunlight, insect and disease pressure and hail damage are stresses that can result in poor stalk quality. Even good growing conditions can lead to stalk problems, when followed by a less favorable environment. Many additional factors, including cropping history, soil fertility, hybrid genetics, and microenvironment effects can heighten the problem in particular fields. Growers should monitor their fields as harvest approaches, to identify stalk quality problems and prepare to harvest before field losses occur. This Crop Insights discusses the causes and management of stalk rot problems in corn.
Photosynthesis and Carbohydrate Movement in the Corn Plant
Through photosynthesis, the leaves of the corn plant capture sunlight and carbon dioxide to produce sugars (photosynthate). These sugars are directed to the actively growing organs of the plant. Early in plant development, sugars move to the roots, where they are converted to structural carbohydrates and proteins in the developing root tissues. As the plant continues to grow, photosynthate is directed to the stalk for temporary storage.
Photosynthesis by corn leaves produces sugars.
Upon successful pollination, ear development places a great demand on the plant for carbohydrates. When the carbohydrate demands of the developing kernels exceed the supply produced by the leaves, stalk and root storage reserves are tapped. University studies indicate that during grain fill, about 60% to 70% of the non-fiber carbohydrates in the stalk are moved to other parts of the plant, but primarily the ear (Daynard et al., 1969; Jones and Simmons, 1983). This stalk depletion begins approximately 2 to 3 weeks following silking. Environmental stresses which decrease the amount of photosynthate produced by the plant can force plants to extract even greater percentages of stalk carbohydrates, which preserves grain fill rates at the expense of the stalk.
Many environmental conditions can decrease the amount of photosynthate produced by the plant. Drought stress and low available sunlight are 2 such conditions. Factors which reduce functional leaf area, such as disease lesions, insect feeding or hail damage also reduce photosynthate production.
Corn stalk infected with both Gibberella and anthracnose rot.
As carbohydrates stored in the roots and stalk are mobilized to the ear, these structures begin to decline and soon lose their resistance to soilborne pathogens. High temperatures at this time increase the rate at which the fungi invade and colonize the plant. Though pathogens play a key role in stalk rot development, it is primarily the inability of the plant to provide sufficient photosynthate to the developing ear that initiates the process.
Stalk Rots Often Begin as Root Rots
Stalk-rotting fungi inhabit the soil in the root zone of corn plants, surviving on discarded cells and nutrients excreted by the roots. They are prevented from invading the roots and stalk by metabolites produced by the plant. Though not sufficiently virulent to overcome healthy living tissue, these opportunistic fungi rapidly invade weakened and dying roots. This occurs as the plant directs carbohydrates to the kernels during ear fill, and the roots begin to languish. After the roots are colonized, the infection spreads to the stalk (Dodd, 1983).
Root rot beginning in basal stalk region.
As vascular tissues in the plant become plugged by fungal mycelial growth, water supply to the plant becomes restricted. Wilting and premature death of the plant eventually follows. External discoloration of the lower stalk becomes evident as deterioration of the inner stalk tissue progresses. The structural integrity of the stalk is diminished by this decay, and the plant is susceptible to lodging. Storms and high winds provide the forces needed to topple the weakened stalks.
The Growing Environment
The growing environment has a critical effect on the ability of the plant to provide sufficient photosynthate to the developing ear. Almost any stress applied to the plant will reduce photosynthesis and resultant sugar production in the leaves.
The decrease in photosynthetic rates due to drought stress has been well documented in research studies. Water relations within the plant and CO2 and oxygen exchange are directly affected. In addition, if leaf rolling occurs during drought, the effective leaf surface for collection of sunlight is reduced.
In research studies in which water was withheld from plants beginning at the mid-grain-fill stage, photosynthesis was eventually shut down (Westgate and Boyer, 1985). Subsequent grain development depended entirely on stalk carbohydrate reserves.
Photosynthesis is most efficient in full sunlight. Studies show that the rate of photosynthesis increases directly with intensity of sunlight. One experiment indicated that photosynthesis rates are reduced more than 50% on an overcast day compared to a day with bright sunshine (Moss et. al., 1960). Prolonged cloudy conditions during ear fill often result in severely depleted stalk reserves.
Reduction of Leaf Area
Any reduction in leaf area will limit total photosynthesis. Leaf area may be reduced due to hail, frost, disease lesions, insect feeding or mechanical injury. Whenever functional leaf area is reduced prior to completion of ear fill, stalks will be weakened.
Favorable Conditions Early, Stress During Ear Fill
Even favorable growing conditions can have a negative effect on stalks. If favorable growing conditions exist when the number of kernels per ear is being established (V10-V17), the eventual demand for photosynthate will be large. Each potential kernel represents an additional requirement for translocatable sugars from the plant. If stress conditions develop during ear fill which render the plant unable to produce enough sugars, stalks will suffer.
Research has demonstrated that the number of kernels per ear on stalk-rotted plants is often greater than that of adjacent healthy plants (Table 1). The additional demand for carbohydrates by larger ears often results in greater depletion of the stalk and eventual stalk rot.
Table 1. Comparison of kernel numbers between plants with rotted stalks and adjacent plants with healthy stalks.*
* From Dodd, 1980.
** Significant at the .001 probability level.
Research studies have documented that soil fertility has a profound effect on stalk quality. Most notable are studies which show that a combination of high nitrogen (N) and low potassium (K) can severely reduce stalk quality. Researchers suggest that yearly applications of N and K (actual N, K as K2O) should be approximately in the ratio of 1 to 1 for favorable balance in the corn plant and to reduce the risk of stalk rots and stalk breakage.
High N is associated with greater kernel number, which increases the demand for carbohydrates to the ear. Higher N also aids the movement of these carbohydrates out of the stalk and into the ear by increasing the rate of translocation within the plant.
The role of K in preventing premature plant death has long been established. K functions in the building of leaf and stalk tissue, and in regulating water movement within the plant. Increases in potassium have been associated with increased photosynthetic rate.
Hybrid genetics are an important influence on stalk lodging potential. Some hybrids naturally partition more carbohydrates to the stalk. Though useful in a poor stalk quality year, that trait may limit yield potential in a more normal environment. In the hybrid development process, researchers must be careful to select hybrids with highest harvestable yield potential across many years and environments. Too much emphasis on stalk quality alone could result in lower yield potential most years. Many carefully selected hybrids with very good stalk quality may appear inadequate during a 1-year-in-10 stalk-lodging event.
Certain plant characteristics other than stalk strength per se can influence a hybrid's potential for lodging. Hybrid maturity determines the plant's developmental stage when environmental stresses occur, which impacts stalk quality. Hybrids prone to leaf diseases may lose significant leaf area, weakening the stalks. Susceptibility to specific stalk rot pathogens also increases the stalk-lodging risk.
Oftentimes, small differences between fields, or between areas in the same field can determine whether corn stands or lodges. Differences in soil fertility, soil moisture, plant-to-plant spacing, insect feeding, or wind gusts can push plants past the lodging threshold. These effects are difficult to predict, but scouting fields in the fall can identify problem areas, and early harvest can reduce field losses.
Multiyear research studies show that stalk lodging is increased only slightly at higher plant populations. For example, a summary of Pioneer research from 35 high-lodging environments from 2004 to 2007 showed that percent stalk lodging increased only about 0.5% for each 1,000 plant/acre increase in population (Paszkiewicz and Butzen, 2007.)
DuPont Pioneer Research Emphasizes Stalk Quality
DuPont Pioneer corn breeders use aggressive techniques to weed out hybrids with poor stalk quality, including manual and mechanical push tests which mimic the forces of wind on corn plants. In addition, plants are inoculated with stalk rot organisms where appropriate to ensure that susceptible genotypes do not escape detection. DuPont Pioneer plant pathologists monitor disease incidence and assist breeders in their efforts to inoculate, screen and characterize products. Research trials conducted by DuPont Pioneer corn breeders are designed to measure product performance for all important traits across a wide range of growing conditions.
DuPont Pioneer IMPACT™ plots further test product performance, including characterization of stalk quality, thus determining proper placement of new product releases. DuPont Pioneer uses information from both breeder and IMPACT plots to develop stalk lodging ratings on all its hybrids to aid customers in selecting appropriate hybrids for their fields.
- Daynard, T.B., J.W. Tanner, and D.J. Hume. 1969. Contribution of stalk soluble carbohydrates to grain yield in corn (Zea mays L.). Crop Sci. 9: 831-834.
- Dodd, J.L. 1980. Grain sink size and predisposition of Zea mays to stalk rot. Phytopathology 70 (6): 534-535.
- Dodd, J.L. 1983. Corn stalk rot: accounting for annual changes. Proc. 38th Annual Corn and Sorghum Research Conference. 38: 71-79.
- Jones, R.J. and S.R. Simmons. 1983. Effect of altered source-sink ratio on growth of maize kernels. Crop Sci. 23: 129-134.
- Moss, D.N., R.B. Musgrave and E.R. Lemon. 1960. Photo-synthesis under field conditions. III. Some effects of light, carbon dioxide, temperature, and soil moisture on photosynthesis, respiration and transpiration of corn. Crop Sci. 1: 83-87.
- Paszkiewicz, S.R. and S.T. Butzen, 2007. Corn Hybrid Response to Plant Population. Crop Insights Vol. 17, No. 16. Pioneer Hi-Bred International, Inc., Johnston, Iowa.
- Westgate, M.E., and J.S. Boyer. 1985. Carbohydrate reserves and reproductive development at low leaf water potentials in maize. Crop Sci. 25: 762-769.
Watch GDUs for Clues on Grain Drydown, Harvest Timing
Written by Mark Licht, Iowa State University cropping systems agronomist
After a wet spring and early summer, growers often begin to wonder whether the corn will mature and dry down to optimal harvest moisture in a timely manner. Even with a cooler, damper first half of the growing season, corn still has time to accumulate enough Growing Degree Units (GDUs) to mature and dry down as normal.
The key for growers from now until harvest is to pay attention to GDU accumulation. If the weather stays cool, growers may have to make decisions about leaving corn in the field to dry down or harvest it wetter than the optimal moisture level. If they choose the former course, they may risk losing yield due to ear drop and lodging. If they choose the latter, they may be hit with drying expense or price docks at the elevator.
Here are some tips to keep in mind when scouting and monitoring corn as it matures:
- Fewer GDUs can slow grain maturity. Lack of heat units delays plant development and therefore maturity and drying which can lead to wet corn in the fall. In addition, high nighttime temperatures during the grain-filling period can shorten the duration of grain fill. Grain may dry down more quickly. Keep an eye on temperatures and grain-fill activity.
- During September and early October, temperatures and GDUs can drive substantial decrease in grain moisture. Corn can lose up to a full percentage point of moisture per day in September and 0.5 to 0.75 of a percentage point a day in October. From late October through November, moisture losses rarely top 0.5 percentage points a day and are often 0.25 percentage points or less.
- Occasionally, a cool September will slow drying substantially. This happened in 2009, delaying harvest for many growers.
- Generally speaking, the first fields to reach ear maturity will be ready to harvest first. However, not all hybrids dry down at the same rate. Those with upright ears tend to dry slower than those with ears set at a more horizontal angle. Also note the differences between husk characteristics: More leaves and tighter husks slow drydown. Ears with tips showing beyond the husk tend to dry more quickly. You may have fields that mature first but dry down slower than other fields due to differences in ear physiology.
- A grower who leaves corn in the field to dry down needs to understand hybrid characteristics, particularly stalk quality. When harvest is delayed, some plants drop ears or be more prone to lodging. If you’re leaving corn in the field to dry down, watch the long-range weather forecast (10 to 14 days): If storms seem likely, it may pay to harvest even if corn is wetter than optimal.
Some years, the decision comes down to which option costs less money. Do you expect to lose more through potentially lower yields by leaving corn in the field? Will the cost of drying down wet corn be a greater hit to your wallet? Or are you better off taking a price dock at the elevator for delivering wet corn. Knowing the characteristics of the hybrid and the cost of energy can help you make the best of a disagreeable situation.
Managing Corn Residue in Corn Production
Crop Insights Written by Steve Butzen¹, Clyde Tiffany² and Darren Goebel³
- Excess corn residue can result in reduced and non-uniform corn stands, as corn is less tolerant of residue than soybeans. Variable crop growth may persist throughout the season.
- To avoid stand issues and achieve highest yields, corn residue should be managed during combining, after harvest in the fall, before planting in the spring, and during planting.
- Processing stalks at the corn head and distributing residue evenly behind the combine are first steps in managing residue.
- Primary fall tillage, where practical, is important to begin the process of stalk decomposition. Spring tillage is another opportunity to reduce stalk residue for successful planting.
- Planters should be equipped with residue manager devices to cut and move residue in order to clear a 6- to 10-inch path in front of the planting units.
Managing Corn Residue During Combining
To help ensure uniform stand establishment for highest yields, growers must carefully manage corn residue, especially when planting fields back to corn. Corn residue should be managed during combining, after harvest in the fall, before planting in the spring (if necessary) and during planting.
Management of corn residue should begin at harvest with uniform distribution of chaff and stalks behind the combine. Uniform distribution has advantages for growers in no-till, minimum till or conventional till systems, including better erosion protection, less plugging of tillage or seeding equipment, and improved stand establishment. Success in uniformly distributing crop residue this fall can also help eliminate tillage passes next spring.
Today’s combines, with wider grain platforms and corn heads, concentrate a larger volume of plant material into the same narrow band exiting the combine. This material must then be spread back onto the wide harvest swath, making uniform distribution more challenging.
Combines with header widths of 20 to 30 feet or more may not be adequately equipped to uniformly distribute large volumes of residue. In such cases, adding manufacturer options or after-market equipment to more aggressively manage residue may be needed. Modifying, checking and maintaining existing equipment may also help to improve residue management (See Residue Spreading and Management Tips below.)
Even residue distribution across the entire harvest swath can help avoid stand establishment issues in the spring.
|Residue Spreading and Management Tips
Straw and chaff. Every grain combine discharges 2 streams of material. Straw is the material that passes through the threshing and separating units of the combine. It consists of corn cobs, husks and some cornstalk pieces. Chaff is the material which is blown or otherwise discharged from the cleaning unit (cleaning shoe) of the combine. It contains smaller "chaffy" pieces of plant stalks, cobs or hulls.
Spreaders and choppers. A straw spreader uses blades or rubber batts rotating in a horizontal plane to intercept the exit stream of straw and deflect it behind and to the sides of the combine path. Most pieces of crop residue remain intact. A straw chopper uses a series of metal flails or knives mounted on a horizontal shaft or drum rotating at high speeds to break or cut residue into smaller pieces prior to distributing. A chaff spreader typically uses spinning disks to distribute the fine residue coming from the combine sieves.
Straw spreader vs. straw chopper. Straw spreaders and choppers are interchangeable on most combines, so growers can choose between the 2 (with some combines, a combination of both is available). While the spreader typically distributes residue more uniformly, the chopper can provide more residue cover, since it chops the residue into small pieces before spreading. Most combine manufacturers offer straw choppers as a standard item or option, and few after-market choppers are now available.
Chaff spreaders are most important for crops that produce a lot of light, fine crop material during threshing of grain, such as soybeans or wheat; but they may also be helpful for corn. Chaff is easy to distribute with hydraulically driven single or dual spinning disks with rubber batts attached, mounted to the rear axle. However, because it is lightweight, chaff is difficult to spread beyond 20 to 25 feet with a single disk. Consequently, for harvest swaths greater than 20 feet, dual chaff spreaders may be needed. Swath width and distribution patterns of chaff spreaders can usually be altered somewhat by adjusting 1) the fore-aft position where material drops onto the spinning paddles, 2) the deflectors or shields at various points around the perimeter of the paddles, and 3) the speed (rpm) of the spinners.
Locating spreaders and choppers. Commercial chaff and straw spreaders and straw choppers are now available to fit most combine models. Producers can obtain more information from equipment dealers, Cooperative Extension, and private fabricators. A list is also available from the PNW Conservation Tillage Handbook Series.
Stalk processing at corn head. One option for growers who find their corn stalks challenging at planting is more aggressive treatment of the stalks at the corn head. Crushing, laceration and shredding of stalks at the combine may help in subsequent stalk degradation by exposing them to microbes and weather. Many equipment manufacturers offer optional “knife rolls” or more aggressive stalk rolls to replace standard stalk rolls on corn heads.
Some experts suggest leaving 12 to 18 inches of stalk in the row at combining. In no-till systems where next year's crop will be planted between the old rows, this keeps more residue anchored and out of the row middles. Taller stalks may catch on planters or fertilizer equipment, however.
Corn Residue Management Postharvest
Stover production by corn plants is roughly equal to the weight of grain produced. This means when corn yields exceed 200 bu/acre, stover yields may reach 12,000 to 16,000 pounds/acre. That's over twice the residue produced by most other crops, and over twice the residue necessary to provide 100% soil cover. If residue is not managed properly, this can lead to stand and yield reductions caused by excess residue. Research suggests that corn yields may be reduced when fields have 90% residue cover within 2 inches of the seed furrow.
Fall tillage. Corn residue is more resistant to decomposition than that of many crops, which can compound the problem of excess residue. Residue that is not incorporated in the fall will largely remain intact in the spring because the decomposition process is slowed even more without soil contact. In general, 5% to 10% more corn residue is decomposed when tillage occurs in the fall than in the spring.
Primary tillage in the fall accelerates residue decomposition.
Most primary tillage implements, including chisel plows, mulch rippers, disk rippers, etc. are designed to incorporate some but not all of the crop residue on the soil surface. In addition, depth and speed of tillage, and type of shovel or point selected will determine the amount of soil moved and residue incorporated. On flat soils not subject to erosion, moldboard plowing is still an option for burying the most possible residue. Equipment manufacturers and extension ag engineers can provide guidelines regarding percent residue incorporation by tillage implement type and operation.
A relatively new approach to fall residue management is the use of "vertical" tillage implements to size residue prior to primary tillage. This equipment, employing narrowly spaced ripple coulters, is operated at high speeds of 9 to 10 miles per hour for most effective sizing of stalks and root balls. High horsepower is generally required for this operation.
Zone tillage. "Zone" or "strip" tillage is a crop production system that combines the soil warming and drying benefits of tillage with the soil conservation benefits of no-till. In this system, a strip 6 to 8 inches wide is tilled in the fall, and the remaining inter-row space (usually 22 to 24 inches) with its crop residue cover remain undisturbed. Tillage is usually accomplished using a shank and knife to lift the soil and disk blades to contain the loosened soil and form it into a raised ridge or berm. In most cases, fertilizer is applied during this tilling operation. In the spring, the tilled strips dry out and warm up much like a conventionally tilled field. The planter units follow these tilled strips, dropping seeds into the center of the raised berm, and often applying additional fertilizer.
Chopping stalks postharvest. An alternative approach to fall tillage is fall chopping of stalks with a flail-type or rotary blade chopper. Although very effective at sizing residue, this approach is not always desirable. Because it flattens the residue profile and distributes stalk residue between the rows, it reduces the advantage of planting next year's crop between last year's rows. Flattened residue is also more prone to "matting" on the soil surface, resulting in cool, wet soils in the spring. Chopped stalks will reduce the percent residue cover by 4% to 8%.
Grazing or baling stalks. Cattle producers may consider grazing their field or baling some of their corn stalks for feed or bedding. A few growers may also have the option of selling corn stalks for ethanol production. In most cases, only a portion of the stalks should be removed so that the benefits of stalk cover are not completely lost. Strategically removing stalks from less-erosive field areas in alternating strips year-to-year is recommended.
Remember that stover contains valuable nutrients – about 17 pounds of N, 4 pounds of phosphorus, and 20 pounds of potassium per ton. If residue is removed, these nutrients will need to be replaced by increased fertilizer rates. For that reason, growers should consider the replacement cost of residue when deciding whether to remove it from the field.
Fall application of N to stalks? Field research has not shown accelerated breakdown of crop residue due to fall N application. In Corn Belt states, microbial decomposition of residue is limited by low temperature, not soil N.
Spring Residue Management Prior to Planting
Secondary tillage in the spring can further reduce residue ahead of the planter. The chart below provides guidance on how much residue tillage tools will bury.
* Add 5% to 10% if primary tillage is in spring rather than fall.
Whether tillage or stalk chopping was performed in the fall, it is important to bury residue as early as practical in the spring if the goal is to reduce high residue loads. Following are tips for successful seedbed preparation when corn residue is excessive on the soil surface:
- Use twisted shovels on chisel plows instead of straight points. Twisted shovels will move more soil, which will in turn bury more residue and fill in deeper harvest ruts.
- Experiment with speed and depth to get desired results. Faster speeds and deeper working depths will move more soil.
- Make sure tillage tools are level fore to aft and side to side across the entire width of the machine. This helps ensure a level soil profile when you are done.
- To minimize soil compaction, avoid tilling wet soils, use tracks or radial tires set to low inflation pressures (6 to 8 psi), and use tillage tools with points instead of disks whenever possible.
Corn Residue Management at Planting
In recent years, the level of corn residue remaining in the spring has increased significantly in many fields. This may be due to changes in several production practices: 1) higher plant populations and superior fertilization practices that increase corn grain yields also increase stover yields, 2) use of foliar fungicides and Bt traits results in improved corn stalks that resist decomposition, and 3) reduced tillage practices result in less residue breakdown.
Corn plants emerging through previous corn residue.
In these fields, growers must manage corn residue properly or risk stand establishment issues. This is especially important in corn following corn, as corn is less tolerant of residue than soybeans. Residue reflects sunlight and insulates the soil, reducing both warming and drying of fields in the spring. This may prevent early planting, or result in reduced or non-uniform emergence. Uniform emergence is critical to optimizing yield potential in corn. Plants that emerge later than their neighbors may be out-competed throughout their development, and yield may be reduced proportionately to their delay.
Corn-following-corn field shows delayed tasseling in strips with excessive residue left by combine.
|Issues Created by Corn Residue in Row
Left: Plants stunted from excess residue. Right: Normal plants.
The final opportunity to manage corn residue is at the planter. Planter-mounted devices include coulters, clearing discs, sweeps, brushes, and rolling fingers. These residue managers can cut and move residue to clear a 6- to 10-inch path in front of the planting units. This serves to minimize the detrimental effects of residue in the row area while maintaining the benefits of residue on the remainder of the field.
Left: Stunted corn row emerging through excess residue. Right: Normal row.
¹ Pioneer Agronomy Information Manager, Johnston, Iowa.
² Pioneer Area Agronomist, Spicer, Minnesota.
³ Pioneer Area Agronomist, Evansville, Indiana.
Best Practices for Harvesting Wind-Damaged Corn
Below find helpful tips from other growers. Time of day and field conditions will have an impact on what works best in a given situation and you may need to experiment to find the best fit.
Meeting Corn Grain Purity Standards for Specialty Markets
Crop Insights written by Steve Butzen¹ and Morrie Bryant²
- Farmers have contracted to produce white, waxy or other specialty corn types for decades. Non-GMO corn is a relatively new niche market opportunity.
- Countries have imposed their own unique purity standards for non-GMO grain; growers must clearly understand the purity requirements for their market.
- To meet purity standards, growers must take additional steps during planting, growing, and harvesting the crop; and drying, storing, handling and transporting the grain.
- At planting, keeping good records, establishing adequate isolation and cleaning planting equipment and seed tenders are the steps needed to help meet purity standards.
- To prevent volunteer corn in a specialty crop, harvest the preceding corn crop in a timely manner, rotate away from corn, and/or use tillage or herbicides when appropriate.
- At harvest, inspect and clean the combine, grain cart and truck. Harvest a number of “border” rows and segregate that grain to increase the purity of the rest of the field.
- Clean dryers and grain bins thoroughly of all residual grain between commodity and specialty production, then clearly document which hybrid is stored in the bin.
- Allow conveying systems (augers and elevators) to run empty between loads of different grain types, and empty the auger sump or pit of residual grain.
Growing corn for “specialty” or “niche” markets provides an enhanced income opportunity for farmers. The higher price commanded by these markets is due to the additional management and risk associated with producing specialty grains. Additional management is required to meet the purity standards of these markets; the risk is typically that if purity standards are not achieved, the crop may have to be marketed in traditional commodity channels with no pricing premium. Specific contractual obligations may present another layer of risk. This Crop Insights discusses specialty corn markets (with particular focus on non-GMO markets), purity standards for these markets, and management practices to help achieve the purity requirements.
Non-GMO Corn Production
A corn hybrid containing a “biotech” or “transgenic” trait is often referred to as a “Genetically Modified Organism,” or “GMO.” Following their introduction in the mid-1990s, GMO hybrids were adopted by farmers at an unprecedented pace. Today, approximately 95% of the U.S. No. 2 yellow corn crop is grown utilizing biotech or transgenic traits. The remaining 5% of the crop, generally referred to now as the “conventional” or “non-GMO” corn market segment, has essentially morphed into a new niche market for corn.
Though non-GMO production is one of the newest niche market opportunities, specialty corn production is not a new concept; many farmers have contracted to produce white, waxy or other specialty types for decades. In general, the principles of achieving purity standards for 1 type of specialty production apply to other types as well; however, non-GMO production presents some unique challenges. This is primarily because countries have imposed their own purity standards for non-GMO grain, and these standards differ significantly from one another. In addition, non-GMO production for export to the European Union has much more stringent purity requirement than other markets. Thus, the non-GMO market can be best thought of as a series of niche markets, each with its own unique purity requirements.
Asian and European Non-GMO Markets
The primary driver for non-GMO corn has been and remains the Asian export market. Japan and Korea are the 2 major US export customers for this grain. Both countries have GMO label laws in place that require notice on a product label of the presence of biotech traits. Many Japanese and Korean consumer product companies, particularly food companies, choose to source non-GMO corn in order to avoid putting such a notice on their products.
Japan defines non-GMO corn as that corn which is a minimum of 95% corn of no detectable traits. So, Japan has set a 5% threshold of tolerance for unintended or “adventitious” presence (AP) of biotech traits in the corn grain they import. When non-GMO corn is originated in the United States, these tolerance thresholds are risk-managed and usually trade at 3% levels. South Korea, on the other hand, uses a minimum standard of 97%, thus a threshold of tolerance for AP of 3%. These programs often trade at the point of origination at a 2% threshold of tolerance. Finally, Europe has the most restrictive standards for non-GMO, employing a 99.1% level of no detectable GMO traits, or a 0.9% threshold of tolerance for the adventitious presence of these traits.
Figure 1. Percent adventitious (unintended) presence allowed in various specialty corn markets. (Examples of AP include yellow kernels in white corn production, normal starch in waxy production, and any GM trait in production for non-GMO markets.)
United States Non-GMO Markets
A non-GMO domestic market also exists in the United States, although it is relatively small. There are growers and consumers alike who demand choice and prefer to not utilize biotech traits. The primary challenge in this market is that there is currently no standard definition of “non-GMO”; rather, it is typically whatever the particular market wants it to be. This ambiguity presents an obvious challenge for growers; if they fail to clearly understand how their particular market defines “non-GMO”, they could be disappointed when they deliver corn. This applies to all non-GMO production, not just production for US markets. Growers must know for certain if the threshold of tolerance for GMO traits is defined in the contract as 3%, 2%, 0.9%, or some other standard. Clearly understanding these “rules of engagement” is necessary to make the best possible decision about participating in the non-GMO market opportunity.
Achieving Purity Standards for Specialty Corn
After carefully reviewing the purity standards mandated for the specialty crop being grown, producers must implement appropriate production practices to achieve those standards. This includes taking additional steps during planting, growing, and harvesting the crop; and drying, storing, handling and transporting the grain.
Planting the Crop
At planting, record-keeping, isolation and equipment clean-out are the steps generally recommended to help ensure the grain ultimately meets required purity standards.
Record-keeping may be simple or sophisticated, depending on the technology available and grower expertise. As-planted (GPS-tagged) records that are transmitted in real time and backed up for safe-keeping are the most foolproof way to document planting. Electronic “notes” recorded on a smart phone or pad and also backed up in the cloud can be equally effective. Lastly, handwritten notes may still be adequate, but lack the safety advantages inherent in backed-up electronic field records. Taking a picture of handwritten notes with a smart phone can lessen the risk of losing these records. Some contracts may require specific forms of documentation during the production of the specialty crop, including at planting. Be sure you are aware of any such contract requirements.
Isolation: Because corn is a cross-pollinated crop and its pollen is wind-dispersed, providing adequate isolation is at the very core of specialty corn production. In fact, the ability to sufficiently isolate the crop from other corn fields is often the deciding factor when considering specialty production. The degree of isolation required is, of course, closely tied to the level of purity targeted. For many end uses, the buyer will provide isolation guidelines to the grower. These guidelines will always take into account the distance and direction (upwind or downwind) of nearby corn fields, and may also consider the type of corn (e.g., dent or sweet) in those fields. A commonly recommended isolation distance for some types of specialty corn production is 660 ft., but that distance could double when purity requirements are extremely high. Be sure to clearly understand the isolation distance needed to achieve your desired level of purity.
Inadequate isolation distance can often be overcome by using a number of rows of the specialty crop as a “buffer,” segregating the buffer grain at harvest, and selling it as commodity grain if it doesn’t meet the purity standards. “Time isolation” can effectively add to distance isolation. Time isolation involves staggering the planting dates of the specialty and nearby corn to create a pollination “differential.” This practice may be risky if employed as the primary means of isolation, as crop pollination timing interacts with the growing environment and is not completely predictable.
Equipment cleanout at planting: A basic tenet of specialty corn production is cleaning equipment to remove kernels of contaminating (non-specialty) seeds and grain. Planters are reservoirs for contaminating seeds of previously planted hybrids. Each make of planter is different, but a thorough cleaning usually involves removing seeds from each individual seed metering unit in addition to the seed hopper(s). The planter owner’s manual should provide tips on proper cleanout procedures, which may also be available online. Growers may also want to check for any videos demonstrating planter cleanout at youtube.com or other websites. Seed tenders, including the box and auger, must also be cleaned to prevent mixing or commingling of seeds.
Growing the Crop
In most cases, there are no visual differences between corn hybrid plants, whether they are GMO, non-GMO or any number of other specialty grain types. That makes it difficult or impossible to identify and destroy unwanted plants prior to harvest. Thus, all possible steps should be taken to prevent possible inclusion of off-type seeds at or prior to planting.
Some unwanted plants in a specialty corn field are not sourced from the planting equipment; rather, they are volunteer corn plants from ears or grain left in the field from previous crops. When volunteer plants grow from a dropped ear of corn, they usually grow in a thick bunch that precludes the development of grain on any of the volunteer plants. However, tassels may be produced on some plants, leading to pollen mixing with the new crop. Just like pollen drifting in from a nearby field, this pollen mixing would reduce the purity of the specialty grain. Thus, all measures should be taken to prevent volunteer corn in a specialty crop, including timely harvest of preceding corn, rotation away from corn, and use of tillage or herbicides when appropriate.
Harvesting the Crop
Harvest presents an opportunity to increase the purity of the specialty crop, as well as a risk of decreasing it. Harvesting a number of “border” or “buffer” rows from the perimeter of the field and segregating that grain can increase the purity level in the remainder of the field. For example, harvesting 16 to 24 rows from the windward (usually south or west) side of a field may be recommended when there is a corn field nearby in that direction, especially if the isolation distance is at or below the suggested minimum.
The risk of decreasing crop purity comes from the chance that significant off-type grain is still present in the combine, grain cart or truck. Inspecting and cleaning the grain cart or truck is a rather simple and basic process; doing the same for the combine is significantly more complex.
Combine clean out: If the combine has been thoroughly cleaned before storing the previous winter, harvesting the specialty field before any others can save a cleaning. Otherwise, additional steps are likely needed – studies have shown that as much as 1 to 2 bushels of grain may remain in the combine, even after running the unloading auger empty for a full minute.
The first step in combine clean-out is to determine what level of purity is needed. For some grain uses, simply “flushing” the existing grain will be adequate. This is accomplished by harvesting a load or partial load of the specialty hybrid and using that load for commodity grain. While negating any premium opportunities for those bushels, this method of clean-out may still be much more cost-effective than labor-intensive cleanout procedures.
Some types of specialty production (e.g., non-GMO production for European markets), may require a more thorough combine cleaning. Details for systematically cleaning the entire combine vary by brand and model. Consult your operator’s manual for manufacturer instructions, or search for instructions or videos online. Then follow a systematic plan to clean specific areas in the machine, usually going from top to bottom and entry to exit. Be sure to conduct cleanout procedures with the utmost safety in mind, including blocking the head and removing the key when workers will be in harm’s way. Cleanout may involve running the machine 1 or more times during the process – be sure all workers are clear of the machine.
Drying and Storing the Grain
Clean dryers and grain bins thoroughly of all residual grain. Growers generally do a good job of cleaning these areas between crops, such as corn and soybeans. Applying the same discipline to cleaning between commodity and specialty production may be needed to meet purity standards for some grain uses.
In addition to cleaning, labeling and record-keeping are important to maintain the identity of grain in storage. Clearly document the hybrid, cleaning procedures and other information according to the intended end use or contract requirements.
Handling and Transporting the Grain
The existing commodity grain handling system is designed to store, transport, and distribute billions of bushels of crops. Growers, grain handlers, and processors did not have special segregation of crops in mind when they built bulk-handling systems. Consequently, there are numerous ways that adventitious presence may occur during grain handling and transport. Commonly referred to as "mechanical mixing" or commingling, these include mixing of grain in harvesting, handling (conveying systems), hauling or in processing equipment or storage facilities.
Conveying systems: Auger and elevator contamination can be minimized by allowing conveying systems to run empty between loads of different grain types. Also, the auger sump or pit should be emptied of residual grain. If additional purity is needed, this can be followed by flushing the system with the new grain and placing the flushed grain in a mixed grain bin.
Grain Cart/Trucks: Clean all obvious surfaces where grain may reside, including horizontal ridges inside of the grain cart. The vertical auger sump in grain carts may have a clean-out shield at the base.
Maximizing Genetic Purity of Specialty Corn
¹Agronomy Information Consultant, DuPont Pioneer
²Sr. Marketing Manager, DuPont Pioneer
Reducing Harvest Losses in Soybeans
Field Facts written by Steve Butzen, Agronomy Information Manager
Minimizing soybean harvest losses can mean substantially higher yields and profits. Extension agricultural engineers suggest that good harvest practices can reduce losses to near 3%, or only 1 to 2 bu/acre. However, delayed harvest or poorly adjusted equipment can result in losses of 10% or more. Since soybeans dry very quickly, close monitoring of grain moisture is required for timely harvest. In addition, combines must be properly adjusted, frequently checked and carefully operated to minimize losses.
Timely Harvest of Soybeans Important
Soybeans should be harvested the first time they reach 13-14% moisture. Moistures above 13% incur a price discount, but moistures below 13% result in less weight at the elevator. The loss of saleable weight can be more substantial than typical discounts for wetter grain, so growers should avoid delivering overdry soybeans. In addition to lost income, harvest losses are also increased when soybeans are harvested too dry.
Soybeans dry very quickly after reaching maturity. At physiological maturity (R7), grain moisture is over 50%, but a harvestable moisture of near 13% can be reached in as little as 2 weeks under good drying conditions. In order to time harvest perfectly, it is necessary to monitor soybean drying very closely. At full maturity (R8), 95% of pods have reached their mature pod color. From this point, only 5 to 10 good drying days are needed before harvest. Begin checking grain moisture before all the leaves have dropped off all the plants, since various stresses can cause soybeans to retain some leaves. It is not uncommon to see a few green leaves and stems on some plants after the pods are fully ripe and the soybeans are dry enough for harvest.
When harvest is delayed, a number of potential losses may occur, including increased tendency to shatter. Soybeans at harvest stage lose and re-absorb moisture readily, and after several such cycles of wetting and drying, are predisposed to shatter. In addition, delayed harvest often results in losses from increased lodging and reduced grain quality.
Research on Field Losses Due To Harvest Delays
A study conducted at the University of Wisconsin investigated the effects of delayed harvest on soybean field losses. In total, 2 varieties from each of 3 maturity groups were grown in each of 3 years at Arlington, Wis. Initial harvest for each maturity group began 3 to 7 days beyond the R8 stage (full maturity). Other plots were left in the field for periods of 2, 4 and 6 weeks beyond the first harvest date. Yield losses as a percent of total yield are shown below:
Source: University of Wisconsin
Yield loss was greatly affected by year. In year 1, field losses after 2 to 6 weeks of harvest delay were only slightly higher than normal field losses with no delay. But losses due to harvest delay in both years 2 and 3 were over twice that of year 1. Losses increased with weeks of delay in all years tested.
Preharvest, shatter and stem losses increased with harvest delays, but stubble and threshing losses remained constant across delays. Gathering unit losses accounted for 60% of total losses.
Monitoring Harvest Losses
Four soybeans in a 1-foot-square area are equal to a 1 bushel loss per acre. Harvest losses should be checked in front of the combine, behind the header, and in back of the combine to pinpoint causes of loss. Ag engineers suggest checking losses in a rectangular area across the entire width of the harvest swath. A 10-square-foot rectangle is suggested as a standard size. Forty soybeans in a 10-square-foot area translates into a 1 bushel per acre loss. A 10-square-foot frame can be built out of rope, with small metal stakes (heavy wire or nails) at the corners to insert into the ground. The length of the frame should be the width of the combine header. The width of the frame needed to equal 10 square feet of area is shown below:
A convenient means of measuring losses is to stop the combine and back up about 20 feet. Losses are determined in 3 areas: in the standing soybeans, behind the combine, and 5 to 10 feet behind the standing soybeans. Set the frame across the entire swath width in the standing soybeans. Soybeans, pods, or broken stems on the ground here represent preharvest losses. Count the number of soybeans shelled and in pods on the ground within the frame. Forty soybeans is equal to 1 bushel loss per acre.
Now move the frame to an area behind the combine and count again. Be sure to sort through all crop residue to reveal shelled soybeans and unthreshed pods beneath. Also count soybeans in pods on stubble. These soybeans behind the combine represent total losses. The difference between total losses and preharvest losses represents harvesting losses.
Harvesting losses can be further divided into "gathering" or "cutterbar" losses and machine losses, by checking just behind the standing beans. To make this measurement, set the frame across the entire swath width about 5 to 10 feet behind the standing soybeans. Count and record the number of individual soybeans within the frame that are shelled and in pods, including stubble. This count minus the preharvest count equals the gathering loss. Machine loss is calculated as follows:
|Total loss - preharvest loss - gathering loss = machine loss|
Reduce Harvesting Loss with Proper Adjustment
Though the type of equipment used can impact harvest loss, all equipment must be properly adjusted and carefully operated to minimize losses. Soybeans that never get inside the combine can account for 80% to 85% of harvest losses. These losses occur due to shatter or lost stalks at the header or left on stubble below the cut-height. Other losses occur due to improper threshing and separation at the cylinder and screens. Harvesting losses can be minimized with proper maintenance and adjustment:
- Be sure knife sections and ledger plates are sharp, and that wear plates, hold-down clips, and guards are properly adjusted. Chains and bearings should be properly lubricated, and belts tight.
- Proper reel speed in relation to ground speed will reduce gathering losses. Shatter increases if the reel turns too fast; stalks may be dropped if the reel turns too slow. Use a reel speed about 25% faster than ground speed.
- The reel axle should be 6 to 12 inches ahead of the sickle in most cases. Operate a bat reel just low enough to tip cut stalks onto the platform. The tips of the fingers on a pickup reel should clear the cutterbar by about 2 inches.
- Cut soybeans as low as possible to minimize stubble losses. Excessive stubble heights can result in significant losses, as shown in the following table:
Source: Iowa State University
- Adjust the rotor- or cylinder-concave clearance according to your operator’s manual. Then adjust rotor or cylinder speed for threshing conditions. Generally, operate the rotor or cylinder at the lowest speeds that effectively thresh the soybeans. When beans are tough, rotor or cylinder speed may have to be increased. Decrease rotor or cylinder speed as beans dry to reduce breakage.
- Keep forward speed at about 3 miles per hour for most combines. Slow down for uneven soil surface or other abnormal conditions.
- Stubble losses can also be reduced by planting and cultivating practices. Height of lowest pods is increased by growing soybeans in narrow rows or by higher plant populations within the row.
Pedersen, P. 2006. Combine setting for minimum harvest loss. Soybean Extension and Research Program, Iowa State U.
Philbrook, B.D. and E.S. Oplinger. 1986. Soybean field losses as influenced by harvest delays. Agron. J. 81:251-258.