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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2005-36

Dates Covered: 
October 25, 2005 - November 1, 2005
Curtis E. Young

Reduce Canada Thistle Populations this Fall

Due to the above average temperatures, moisture, and more open crop canopies earlier this fall, Canada thistle plants are much larger than normal for this time of the year. Thistle plants also appear to be remaining intact through corn harvest to a greater extent than usual. Producers can take advantage of this situation to possibly maximize their control of Canada thistle following corn harvest. Where thistle regrowth in early-harvested soybean fields reaches a size of 8 to 10 inches, herbicides can also be effectively used this fall. The most effective treatment for Canada thistle in the fall is glyphosate at a rate of 1.1 pounds acid equivalent. If possible, apply during periods of relatively warm weather and apply before a hard freeze. Do not apply other herbicides, especially 2,4-D ester and clay-based herbicides, with the glyphosate, because they often reduce glyphosate’s activity on thistle. Add ammonium sulfate (AMS) at the rate of 17 pounds per 100 gallon of spray mixture.

Natural Air Grain Drying in Ohio

Authors: Robert Hansen

With higher costs of electrical energy, propane and natural gas this fall, producers are looking for ways of holding down their energy costs for finishing their crops. One option producers may have, if their grain handling systems are properly set up for this option, is natural air drying for shelled corn.

Natural air drying systems can dramatically reduce energy inputs for drying. For example, drying corn from 25.5 to 15.5% moisture content with a natural air system may use as little as 25 to 40% of the total energy of high temperature systems. Natural air drying replaces the fuel energy, usually propane, by using the natural drying potential of air over a longer period of time. However, more electrical energy is used to move the air through the bin. Total energy cost will depend on fuel and electric energy costs but will generally be lower for natural air systems.

In addition to energy savings, well-managed natural air systems can produce a superior quality product for feeding or market. Dry, high quality grain is the objective of any drying and storage system. Grain that is over-dried not only results in excessive drying costs, but also leads to poor quality and loss in market value. Characteristics of poor quality are stress cracks, broken kernels, and fines that result from over-handling, overheating, over-drying and immature kernels. Over-dried grain is less palatable to livestock. Grain that is under-dried leads to mold and associated weight losses due to respiration occurring in the grain. Producers can identify very quickly with costs of poor quality when they experience price discounts in the marketplace.

Natural air drying is an in-bin drying system with the following requirements and characteristics: The bin that will be used for both drying and storage should be equipped with a fully perforated floor, one or more high capacity fans, a grain distributor, and stairs on the outside for easy access for monitoring purposes; Cleaning equipment should be used to remove broken kernels and fines; Initial moisture content of the grain coming out of the field should average between 22 to 24%; Grain handling is minimized by not moving it through multiple bins (holding to drier to storage); Drying results from forcing unheated air up through the grain mass at airflow rates of 1 to 2 cubic feet per minute per bushel of grain (cfm/bu); and The drying process is slow, generally requiring 4 to 8 weeks.

The key to natural air drying is airflow. Rate of airflow is measured in cfm/bu. A typical airflow rate is 1.25 cfm/bu. Since the volume of one bushel is 1.25 cubic ft, an airflow rate of 1.25 cfm/bu would imply a complete air change for each bushel of grain every 0.5 minute if the pore space is 50%. Since drying rate is proportional to airflow rate, if the airflow rate is doubled, the grain drying rate doubles. Successful natural air drying requires enough air be provided to complete drying before unacceptable levels of deterioration occur (0.5% is the usual recommended maximum deterioration due to dry matter loss).

Upward airflow is recommended. With upward airflow, the grain at the top of the bin is most critical since it is last to dry. Upward airflow allows the most critical grain to be visually checked by the operator. Airflow must be sufficient to move the drying front (boundary between dry grain and grain that is not yet dry) to the top of the grain before spoilage occurs.

Generally, corn harvesting for natural-air drying should be delayed until October 15 in Ohio for two reasons: 1) to take advantage of the free natural-air drying that occurs in the field, and 2) to reduce the probability of the occurrence of 60 F days after the corn is harvested, stored and not yet dry. As air temperature increases, the time available for drying decreases faster than the drying capacity of the air increases. The only alternative is to increase airflow rates.

Airflow rates for natural-air drying are primarily controlled by fan size, grain type, bin diameter, and grain depth. Practical ranges for fan size and energy requirements limit the airflow rate and also vary according to initial moisture content.

One of the frequently asked questions about using a natural air drying system is, “Should the aeration fans be stopped at night or during humid weather?”

And the answer is, leave the fans running if the bin contains corn wetter than about 16% and the temperature is warmer than about 40 F. If the corn is warm and wet and the fan is off for very long, mold growth might cause the corn to heat. Also, some operation during humid weather is needed to rewet corn at the bottom of the bin that over-dried during dry weather. If the fan only operates during the driest weather, corn will be badly over-dried. Remember, fan heat reduces air relative humidity and allows corn drying even under fairly humid conditions.

If corn is nearly dry and the temperature is low, there is little risk of corn spoilage and it is safe to stop the fan during humid weather. Stopping the fan will save some energy. Regardless of corn moisture, it is usually best to stop the fan during heavy snowfall to avoid plugging holes in the perforated drying floor.

Natural air grain drying systems do require close monitoring to reduce the risks of grain spoilage. Other good management practices that will reduce risks, assist in working with the grain, and increase success of operating a natural air grain drying system include:

1. Grain should be free of excess dirt, fines, and chaff. Cleaning devices are recommended. Not cleaning these materials out of the grain mass can result disruptions of air flow through the entire mass. Areas of heavy deposition of these materials can be so dense that moisture and temperature can not be altered.

2. Keep grain level as bin is filled. Grain leveling devices are recommended. Peaks on top of the grain mass are also difficult to manage with aeration. Air, like water, will travel the path of least resistance. Air will more quickly exit a grain mass through the lowest edges of peaked grain leaving the center of the peaked grain unaerated.

3. Aeration fans should be started as soon as the bin floor is covered with grain and operated continuously until the grain is dry or the average air temperature is below 35 F for extended periods.

4. Leave all roof hatches open to provide a large air exhaust opening, approximately 1 sq ft for each 1,000 cubic feet per minute of air delivered to the bin.

5. Circular stairs up the outside of the bin should be included as standard equipment to facilitate safe and frequent grain inspection.

6. Attach a manometer to the air plenum to measure static pressure and use manufacturer's fan performance charts to determine air flow.

7. When the daily average temperature drops below 35 F, cool the grain to a uniform temperature and turn the fan off (below 35 F drying is slow and inefficient). If moldy odors are detected or the grain starts to heat, turn the fan on until the conditions are corrected. Continue the drying process when the average temperature returns to 35 F or above.

8. After drying is completed, close the roof hatches and cover fan inlets to prevent migrating air from adding moisture to the grain.

9. Do not exceed design criteria for the aeration fans. When necessary, limit grain depth to obtain proper air flow in relation to grain moisture content.

10. Follow safety rules at all times while working in or around grain bins and drying equipment.

For more detailed discussion about recommended airflow rates for specific grains at various moisture contents, effects of bin diameters and grain depths, fan selections, how to determine when grain drying is complete and other specifics of natural air grain drying, view the following two publications:

An additional resource for natural air grain drying in Ohio is OSU Extension Bulletin 805, “Natural Air Grain Drying: Guidelines for Ohio.” Unfortunately, this bulletin is out of print, thus copies may be hard to find. However, check with your county’s OSU Extension Office for availability of a copy of this bulletin.

2005-2006 State Pesticide Recertification Conferences for Ohio Pesticide Commercial Applicators

Authors: Curtis Young

Two Field Crop Pesticide Recertification Conferences will be held in Ohio in 2005-2006 winter meeting season. The first is scheduled for December 15, 2005 to be held at the Lima Holiday in Lima, Ohio and the second, February 8, 2006 to be held at the Ohio State University Fawcett Center in Columbus, Ohio. The conferences will cover categories that include agronomic pests, agricultural weeds, greenhouse, fruit/vegetable, industrial vegetation, seed treatment, livestock, fumigation, aquatic, forestry, aerial, wood preservation and Core. Registration for the conferences can be done on-line at: or registration forms will be sent to commercial operations in the near future.

Archive Issue Contributors: 

State Specialists: Dennis Mills and Pierce Paul (Plant Pathology), Bruce Eisley and Ron Hammond (Entomology), Jeff Stachler (Weed Science) and Robert Hansen (Food, Agricultural, and Biological Engineering). Extension Agents: Ed Lentz (Seneca), Steve Foster (Darke), Roger Bender (Shelby), Mark Koenig (Sandusky), Gary Wilson (Hancock), Glen Arnold (Putnam), Harold Watters (Champaign), Curtis Young (Allen), and Keith Diedrick (Wayne).

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.