CIRCULAR ANR-243 (09/82)

A L A B A M A    A & M    A N D    A U B U R N    U N I V E R S I T I E S HARVESTING, DRYING AND STORING GRAIN SORGHUM

     Excessive harvesting losses are quite common in grain sorghum. Header losses are often very high, especially when lodging is a problem. The keys to low-loss harvesting of grain sorghum are harvesting at the right time, and doing it with properly operated equipment.

     Grain sorghum should be harvested as early as possible to minimize high combining losses, and losses to birds, insects, mold, and bad weather. In the Southeast, grain sorghum does not normally get dry enough in the field for safe storage until after a killing frost; but waiting for a frost increases the probability of excessive field losses. Therefore, you should plan to harvest sorghum before it reaches safe storage moisture level and to dry it mechanically.
     Mature grain sorghum in the field contains about 30 percent moisture. At moistures higher than 25 percent, the seeds are too soft to withstand the threshing action of combining. The ideal moisture content for harvesting grain sorghum is about 20 percent. At higher moisture content, more losses would be expected in the tailings. At lower moisture content, header losses would probably be higher. Approximate harvesting losses to be expected at various moisture levels are as follows:

     When properly adjusted and operated, a conventional combine will thresh, separate and clean grain sorghum satisfactorily. But the combine must have special adjustments and proper operation to keep harvesting losses low.
     Header losses are often excessive, especially in lodged or overdry sorghum. Header modifications, including cutter bar guard extensions, will reduce these losses.
     When using a conventional header, raise the header as high as possible without skipping too many heads. This will minimize the load on the threshing and separation equipment in the combine.
     The reel tip speed should be about 25 percent faster than the combine ground speed. This allows the reel to pull the heads gently onto the platform as they are cut, and so minimizes shatter losses. The reel should run only deep enough into the heads to gain control, not deep enough to catch under the heads and throw them over the back of the header.
     Row crop headers are ideal for grain sorghum harvesting. Research shows that - under ideal field conditions, row crop headers will save approximately 0.6 percent more grain than a conventional header. But in severely lodged grain sorghum, a row crop header could harvest as much as 40 percent more grain than a conventional grain table could harvest from the same field.

     The threshing action for any crop should be just aggressive enough to detach the seed from the heads. Cylinder speeds of 750-900 rpm are recommended for most combines.
     On most combines, clearance should be about 1/2 inch in front, and 1/8 - 3/16 inch in the rear. Check your operator's manual for recommended cylinder speeds and concave adjustments for your machine, then try it in the field and make exact adjustments.
     Grain sorghum stalks are normally at a higher moisture content at harvest than cornstalks, and are more likely to be chopped up and put into the grain tank. As little material as possible should be returned to the cylinder because some of the recycled material will eventually be broken into pieces small enough to go into the grain tank. The chaffer extension should be closed enough to prevent excessive return, even if it means a slight loss of grain off the chaffer.
     Watch the sieve closely for indications of matting. Matting can lead to excessive grain loss. Check your operator's manual for recommended adjustments for the cylinder, concaves, chaffer, sieve and fan.

     Check your field losses by remembering that 17 kernels per square foot is a loss of approximately 1 bushel per acre. The following procedure can be followed to estimate your losses, and to determine their cause:

     Wet sorghum cannot be held as long as corn, although farmer experience from other states indicates that holding overnight is not as dangerous as was thought. The sorghum mass packs tighter, allowing less air circulation and encouraging seed germination and mold growth.
     To minimize wet holding risks, follow these pointers:

     Trash and green matter contamination is a more severe problem in drying sorghum than in drying corn. Most Southeastern sorghum is harvested before frost and usually there are many pieces of green stems and leaves to contend with. In the dryer, this trash tends to float and collect in comers, causing a fire hazard and affecting air flow.
     Very trashy sorghum may need to be cleaned both before and after drying. Removing trash before drying decreases the load on the dryer and allows for more uniform drying. However, "wet side" cleaning is difficult because the grain tends to be wet and sticky from the stem juices released during combining, and the grain will need cleaning after drying also.
     Cleaning sorghum is a scalping operation to sieve out the large particles and trash rather than sifting out the fines from the seeds. If you use rotary screens, remember that the grain falls through the screen and the trash is retained. Since most cleaners are designed to retain the grain and drop the fines, you may need to re-orient the take-away conveyors to handle the large volume that falls through the screen.

     Since sorghum seeds are smaller than corn kernels, there is less space between them and therefore more resistance to air flow. At an air flow rate of 10 cfm/bu, a 3-foot depth of sorghum has about as much resistance as a 4-foot depth of corn, as shown in the bar graph below.

     Reports indicate that more fires occur in sorghum drying than in corn drying. One reason is the higher level of trash in sorghum grain. Since this trash dries faster than the grain and may remain through several drying cycles, it can easily reach a "tinder" condition. Here are the steps to take to reduce fire risk to a minimum:

     Any drying method used for shelled corn should also work for sorghum, subject to the limitations of lower air flow and, hence, capacity. Bin drying should be similar to corn if drying depths and layers are reduced 25 to 40 percent.
     For long-term storage, sorghum should be dried to 12 percent moisture.
     Corn and sorghum can be layered or mixed if the grain is to be used for livestock feed. Either can be placed on the bottom, but the overall depth or layer thickness should be reduced to compensate for the added flow resistance of the sorghum portion of the total.
     Drying air temperatures are essentially the same for sorghum as for corn:

     Procedures used for dryeration, grain stirring and blending can be the same as for corn if allowance is made for the increased air flow resistance of sorghum.

     Dry sorghum stores essentially the same as shelled corn. As mentioned above, it should be cleaned before storing. In addition, it should be mechanically spread or filled to distribute the fines and trash.
     A properly designed aeration system is essential for safe storage. Here are major considerations in the operation of such a system:

     Most of the information contained in this publication was adapted from Harvesting, Drying and Storing Grain Sorghum, AE-82, Purdue University.