Corn: Harvesting and Storage
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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
|
