Corn: Harvesting and Storage
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811: Agronomy Guide > Corn
> Harvesting and Storage
Table of Contents
Physiological maturity (black layering) occurs when
the grain moisture content reaches 31%-33% moisture. After this
stage, there is no dry matter added to the corn kernel. Harvesting
grain corn at moisture contents above 28% often results in significant
damage to the grain and makes it more difficult to market commercially.
High quality food grade markets may require harvest moistures to
be as low as 20%-22%.
Weigh the benefits of delaying harvests to lower drying
costs and improve sample quality against the increased risks that
come from higher levels of stalk lodging, ear drop and wet weather.
Determine the need to adjust harvesting dates forward to prevent
harvest losses by scouting fields and checking for stalk quality.
When stalk quality is poor, the next significant wind or rainstorm
may increase harvest losses dramatically. Efficient header performance
is also important when harvesting corn with poor stalk strength.
Keep header speed in step with ground speed to improve stalk flow
down through the stripper plates and snapping rolls. If necessary,
adjust them closer together.
Damage to grain quality by the combine can result from any of the following:
When harvesting corn that has been frozen prior to maturity, experience
generally indicates that running the cylinder speed as slow as possible
is the key to maintaining quality.
Use these guidelines to assess combine harvest losses:
If combine losses exceed 0.16 t/ha (2.5 bu/acre), make adjustments.
The three general types of grain dryers used on the farm are:
No single drying system is superior to all others in every respect.
Grain drier selection is dependent on desired features including
drying capacity, grain quality, fuel/drying efficiency (BTUs per
volume of water removed), convenience, manpower required to run
the dryer, ability to dry a variety of crops, maintenance required
and capital cost.
All dryers move "dry" air past the grain to evaporate moisture within the kernel and carry the water vapour away. Heat is added to this drying air to reduce its relative humidity, thereby increasing its ability to pick up moisture. Wet grain can be dried at higher temperatures, without damaging the corn, because the corn is cooled as the moisture evaporates from the kernels. As the grain dries, it will approach the temperature of the drying air. The longer grain kernels are in contact with this heated air, the drier and hotter the kernels will get.
Corn dries as the moisture from the inside of the kernels is evaporated
from the kernel surface. Most of the moisture inside the kernel
exits through the tip end of the kernels. The first few points of
moisture can be easily removed using relatively little energy. Further
moisture must be removed from deep within the corn kernels. As the
outside layers of the kernel dry, the moisture must migrate out
from the moist centre. This moisture does not move to the surface
as quickly as it is being evaporated from the surface of the kernel
by the drying air. This results in higher energy requirements to
remove the last few percentage points of moisture.
A range of drying temperatures can be used to dry corn but should
not exceed the maximum recommended air temperatures in Table
1-27, Maximum Recommended Air Temperatures for Drying Corn of Various
End Uses. The maximum recommended drying temperature depends
on several factors, including final end use of the grain, initial
moisture content of the grain, type of grain and type of dryer.
Viability is destroyed when the actual grain temperature exceeds approximately 50°C. Reduction in nutritional value occurs when grain temperature reaches 90°C-100°C.
Taking corn hot out of the dryer, allowing it to steep for a time
and then aerating the corn with a minimum of 6.5 L/sec/m3 (0.5 CFM/bu)
airflow will reduce stress cracking.
Stress cracking and physical kernel damage are influenced by the
speed of moisture removal and maximum kernel temperature, coupled
with the rate of cooling after drying.
In addition to maintaining grain quality, using this system of dry-aeration or cool-aeration can increase the throughput of the drying system. Many farmers in Ontario practice "cool-aeration," where corn is removed hot from the drier, transferred to a storage bin and cooled slowly. In this way, hot corn is continuously being added to the top of the final storage bin and slowly cooled.
Natural-air drying of corn is possible in most parts of Southern Ontario. This method of drying corn is well suited for livestock operations to produce high-quality corn that is free of stress cracks. Good management of a natural-air drying system is critical to success.
Fan operation in a natural-air corn-drying bin is slightly different
than for other air-dried crops. Once there is sufficient corn in
the bin to hold the perforated floor down, the fan can be turned
on. Run the fan continuously for the first 3 weeks after the bin
has been filled or until the first drying front has come through
the top of the bin.
The first drying front emergence will be evident when there is a noticeable drop in the moisture content of the corn at the top of the bin. Before this drying front passes through, the corn at the top of the bin will remain at harvest moisture levels and may even increase slightly compared with the corn drying further down. If the fan is shut off for an extended period of time at the start of the drying process, there is a risk that the drying front may stall and will not move upwards once the fan is turned on again. This will result in spoilage occurring above the drying front.
Rain or shine, the fan should not be turned off until the first drying front has passed through the whole bin.
Once the first drying front passes through the top of the bin,
begin to manage the fan operation, using the equilibrium moisture
chart for corn see Equilibrium Moisture Content.
Run the fan any time the outside conditions will still allow the
wettest corn in the bin to dry. At times, this procedure may add
some moisture to the corn at the bottom of the bin. This temporary
rewetting of the bottom corn will actually dehumidify the air so
it can do more drying up higher in the bin.
The corn may not reach the desired moisture content before freezing weather arrives. Trying to accomplish natural-air drying in below-freezing temperatures is very slow and inefficient. The last few points of moisture may have to be taken out in early spring. Some livestock producers never finish drying the corn any further after winter, since it processes and stores well as feed at the higher moisture levels.
Humidistats are available that will activate the fan at preset humidity levels. The operator can adjust and set the relative humidity level at which the fan is activated. Bins with stirrators will have fairly uniform moisture levels throughout the whole bin as a result of the mixing that has occurred. Corn at moisture levels greater than 25% can also be dried in a natural-air bin. This is accomplished by only partially filling the natural-air bin, resulting in an airflow of 52-78 L/sec/m3 (4-6 CFM/bu). Producers who need corn for feed in late September can harvest headlands and put this in the bin. The warm temperatures in late September, combined with higher CFM/bu airflow enable this corn to be dried in a couple of weeks.
Researchers have developed equilibrium moisture content tables that predict the final moisture content of corn when exposed to air at a certain temperature and relative humidity Table 1-28, Equilibrium Moisture Content for Corn Exposed to Air. For example, to determine the equilibrium moisture content of corn exposed to outside air at 10°C and 70% relative humidity, find the point at which the 10°C line and the 70% relative humidity line intersect. This point (15.4%) will be the equilibrium moisture content.
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