Drying the 2011 Corn and Soybean Crops

Sam McNeill, Extension Agricultural Engineer, University of Kentucky

Wet weather this spring delayed corn and soybean planting in many areas and consequently pushed harvest later this summer.  Good drying conditions normally occur in September and October and will reduce operating costs for all drying systems.  Moreover, high temperature automatic batch and continuous flow dryers can be used to partially dry corn to 16 or 17 % moisture and unheated, natural air drying can be used to finish drying to the market level (normally 15.0%).  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.



Table 1. Equilibrium moisture content of yellow corn (%wb) at different temperature and relative humidity levels (shaded area represents safe storage levels through March).

Temp.	Relative Humidity (%)
F	40	50	60		65	70	80	90
40	11.5	12.9		14.5	15.3	16.2	18.3	21.3
50	10.9	12.3		13.8	14.7	15.5	17.6	20.5
60	10.3	11.8		13.3	14.1	15.0	17.0	19.9
70	9.9	11.3		12.8	13.6	14.4	16.4	19.4
80	9.4	10.8		12.3	13.1	14.0	16.0	18.8

Table 2. Equilibrium moisture content of soybeans (%wb) at different temperature and relative humidity levels (shaded area represents safe storage levels through March).

Temp.	Relative Humidity (%)
F	40	50	60		65	70	80	90
40	7.7	9.3		11.3	12.6	14.2	18.9	28.6
50	7.6	9.1		11.1	12.4	14.0	18.6	28.2
60	7.4	9.0		10.9	12.2	13.7	18.3	27.8
70	7.3	8.8		10.7	12.0	13.5	18.0	27.4
80	7.2	8.6		10.6	11.8	13.3	17.7	27.0

Two other pieces of useful information when considering timely harvest is the amount of time required to dry corn (Table 3) and the allowable storage time (Table 4).

Table 3. Approximate number of days needed to dry the top layer of corn from the initial/harvest level shown to 17% moisture with air at 65 F and 60% relative humidity (Source: Granary, 1994).

Moisture Concentration,	Airflow, cfm/bu
%	1	2	3
18	19	10	6
19	22	11	7
20	25	13	8

For natural air drying, note that drying times are proportional to airflow rate (cubic feet of air per minute) for each wet bushel (cfm/bu) for all moisture levels.  Adjust grain depth in a bin to control the drying rate.  In Table 4, note how much cooler temperatures add to storage life, which emphasizes the importance of drying and cooling grain as soon as possible in late summer/early fall. For example, corn at 20 percent moisture and 60 degrees will only have about 25 days to dry in a bin, which is about the time needed to dry at 1 cfm/bu (Table 3).  Thus, grain depths must be shallow enough to provide more airflow (preferably 2 cfm/bu) to dry the crop well before sprouting or mold damage occurs.

Table 4. Allowable storage time in days for corn (Source: ASAE, 2000).

Moisture Concentration	Temperature
%	40	50	60		70	80
16	*	230		120	70	40
17	280	130		75	45	20
18	200	90		50	30	15
19	140	70		35	20	10
20	90	50		25	14	7

The last piece of information needed to manage natural air drying systems is the amount of air the fan can provide at different depths in a bin.  Table 5 shows an example of a 10 horsepower fan on a 36 feet diameter bin.  In this case, grain depths of 6.5, 9 and 16 feet provide airflows of 3, 2 and 1 cfm/bu, respectively, which can be used to estimate drying capacity and fan operation times.

Table 5. Air delivered at different depths in a 36-ft bin with a typical 10 hp axial fan.

Depth						Static Pressure
Ft	Bushels		CFM		cfm/bu	(in. H2O)
2	1,629		16,660		10.2	0.42
4	3,257		16,180		5.0	0.80
6	4,886		15,700		3.2	1.15
8	6,514		15,280		2.4	1.47
10	8,143		14,820		1.8	1.77
12	9,772		14,400		1.5	2.03
14	11,400		14,040		1.2	2.29
16	13,030		13,700		1.0	2.53
18	14,660		13,340		0.9	2.74
20	16,290		13,000		0.8	2.94

More information on these and other grain drying systems and settings for 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.htm).  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.