Drying The 2009 Corn And Soybean Crops
LEXINGTON, KY.
The cool wet fall has drastically
delayed normal field
drying of corn and soybeans
and will add to operating
costs for all drying
systems. High temperature
automatic batch and continuous
flow dryers will require 10
to 15 percent more energy per
bushel because of the cool, humid air which has
less moisture holding capacity than normally
seen in the fall. Producers who usually rely on
natural air drying in the bin may want to consider
installing a low temperature burner or
using a space heater to add between 5 to 10 degrees
to the outside air. This will lower the humidity
of humid/night time air by roughly 10 to
20 percent, respectively, and speed up drying. If
too much heat is added, grain in the bottom of
the bin will be overdried, which adds considerably
to drying costs and market weight loss.
Drying limits for corn and soybeans are shown
in Table 1 and 2, respectively. These are the
moisture levels each grain will reach after sufficient
exposure to the air conditions shown. For
example, at 50 degrees and 70 percent humidity,
corn will reach 15.5 percent moisture and
soybeans will reach 14.0 percent moisture.
Tracking the average weather conditions during
fan operation is important for maintaining appropriate
grain moistures within the bin.
Two other pieces of useful information to consider
during harvest are the allowable storage
time (Table 3) and the amount of time required
to dry corn (Table 4). Cooler temperatures add
to storage life, which has been about the only
saving grace this fall. Use the information from
tables 1 and 2 to predict similar conditions for
soybeans. For example at 60 degrees and 70
percent humidity, soybeans at 13.7 percent
moisture have a similar storage time as corn at
15.0 percent moisture, which is 120 days. Note
in Table 4 that for some drying situations the
amount of time required to dry the crop can exceed
safe limits with the poor weather conditions
typical in November and December.
Another important piece of information
needed to manage natural air drying systems is
the amount of air the fan can provide for different
depths in a bin. Table 5 shows an example
of a typical 10 horsepower axial fan on a 36 feet
diameter bin for both corn and soybeans. In this
case, airflows of 3, 2 and 1 cfm/bu are possible
at corn depths of 6.5, 9 and 16 feet, respectively,
and soybean depths of 6.7, 9.6, and 18,
respectively.
The relevant point here is that corn at 20 percent
moisture and 60 degrees will only have
about 25 days to dry before some losses occur,
so grain depths must be fairly shallow to provide
enough airflow (greater than 2 cfm/bu) to
dry the crop before sprouting or mold damage
occurs. In the example given, once the top layer
of corn is dried to 17 percent moisture (18 percent
for soybeans), an 8-ft layer can be added
to maintain an airflow of 2 cfm/bu. Cool all
grains to 35 to 40 degrees to add storage life and
consider either selling before next spring or finish
drying then.
More information on different grain drying
systems and their efficient operation is provided
in Chapter 10 of the publication ID-139
“A Comprehensive Guide to Corn
Management in Kentucky”
(www.ca.uky.edu/agc/pubs/id/id139/id139.ht
m). Additionally, a list of publications that describe
specific drying systems is provided in the
document. These may be ordered from county
extension offices or by calling Joyce Peel at 859-
257-3000 x 111. Δ
DR. SAM MCNEILL: Biosystems And Agricultural
Department, University of Kentucky
Table 1. Equilibrium moisture content of yellow corn (% wb) at different temperature and relative humidity levels
Table 2. Equilibrium moisture content of soybeans (%wb) at different temperature and relative humidity levels
(shaded area represents safe storage levels through March).
Table 3. Allowable storage time in days for corn (Source: ASAE, 2000).
Table 4. Approximate number of days needed to dry the top layer of corn to 17% moisture (Source: Granary, 1994).
Table 5. Air delivered at different depths in a 36-ft bin with a typical 10 hp axial fan.