Corn: Harvesting and Storage
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Pub 811:
Agronomy Guide > Corn
> Harvesting and Storage
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811: Agronomy Guide for Field Crops
Table of Contents
Corn Harvest
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:
- cylinder speed too high
- concave clearance too narrow
- too many concave filler bars
- concave and cylinder not parallel
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:
- 22 kernels per square metre (2 kernels per square foot) represents
approximately 0.06 t/ha (1 bu/acre) in losses
- one average-sized ear in 1/100 acre (6.4 x 6.4 m (21 x 21 ft)) represents
0.06 t/ha (1 bu/acre) in lost yield
If combine losses exceed 0.16 t/ha (2.5 bu/acre), make adjustments.
Harvesting and Storing Corn Silage
Haylage and Corn
Silage.
Corn Storage
Drying and Storing Corn
The three general types of grain dryers used on the farm are:
- in-bin
- batch
- continuous flow
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.
Drying Corn With Heated and Unheated Air
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.
Table 1-27. Maximum Recommended Air Temperatures
for Drying Corn of Various End Uses
|
End Use
|
Maximum Drying
Temperature (°C) |
Seed corn
|
45
|
| Starch milling |
70
|
| Industrial uses, non-ruminant feed |
90
|
|
Cattle feed |
120
|
Drying Temperatures
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.
Kernel Quality
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
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.
Minimum Requirements for Natural-Air Drying
- full aeration floor in the bin
- level grain surface across the whole bin
- minimum airflow of 26 L/sec/m3 (2 CFM/bu), preferably more
- corn 25% moisture content or less
- clean corn with no cob pieces or fines
- accurate moisture reading of the corn in the bin
- accurate outside air temperature and relative humidity measurement
- an understanding of corn equilibrium moisture content
- coring the bin (auger out some grain) after filling. The best way
is to remove a couple of loads from the bin. This establishes the flow
funnel and removes the highest concentration of fines from the centre
of the bin. Clean these loads before placing them back into the bin.
Even if the loads are put right back in the bin without cleaning, the
resistance to airflow will be less than if the bin had not been cored.
- an on/off switch for the fan
When to Run the Fan
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.
Equilibrium Moisture Content
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.
Table 1-28. Equilibrium Moisture Content
for Corn Exposed to Air
|
Temperature °C
|
Relative Humidity (% Wet Basis)
|
|
50%
|
60%
|
70%
|
80%
|
90%
|
|
0
|
13.7
|
15.1
|
16.6
|
18.4
|
21.3
|
|
5
|
13.1
|
14.4
|
15.9
|
17.8
|
20.7
|
|
10
|
12.5
|
13.8
|
15.4
|
17.3
|
20.2
|
|
15
|
11.9
|
13.3
|
14.9
|
16.8
|
19.8
|
|
20
|
11.5
|
12.8
|
14.4
|
16.4
|
19.4
|
|
25
|
11.0
|
12.4
|
14.0
|
16.0
|
19.0
|
