One general principle applies when harvesting corn — the grain should be dried or delivered quickly, preferably within 24 to 48 hours of harvest, suggests Paul Sumner, University of Georgia Extension agricultural engineer.
“Equipment and operations that have worked well when corn was harvested at 22-percent moisture may not work so well when the corn is wetter,” says Sumner. “Combines often have much greater capacity than driers when the corn is very wet. You can start harvesting at about 30-percent moisture if you want to, but it would be more economical to start lower.”
When you do get started harvesting, it’s important to know how long you have from the time you begin until the corn is field dried, with field dried being about 15 percent, he says. “This past summer, there was a two to four-week window when you could get it harvested. Then, after it’s field dried, you have just a little longer before you start having problems. Bad weather could set in, and the quality of your grain will go down,” he says.
If you haven’t been growing corn much in recent ears, your combine probably isn’t very efficient, says Sumner. “It is important that your combine capacity matches your drying capacity if you’re going to dry it yourself. Look at it as a 24-hour period. You’re only going to combine 14 to 16 hours per day, but you can dry 24 hours per day,” he says. If it has been a poor growing season, aflatoxin could be a problem for some growers, especially in dryland situations, he adds. “If you don’t have any drying capacity, field drying probably is the worst scenario. Once the corn is field dried, your window of opportunity for harvesting is very limited.”
Growers need to decide if they’re going to store corn on the farm or if they’re going to let the grain dealer handle it for them.
“And if you handle high-moisture corn, how will you dry it? It is important to know the storage capacity on your farm. Is your dryer in top condition, or will you deliver it to an elevator with drying capabilities? If the grain dealer doesn’t have drying capabilities, he’ll dock you, and the dockage may be significant compared to drying it yourself.”
There’s also the possibility of custom drying, he says. This most likely would involve a neighbor who may not have started harvesting or who already has finished. Or, in south Georgia, this could include peanut drying points, says Sumner.
Costs for such a service would include a drying charge and handling fee, he says. Custom services could be used to boost drying capacity or as a supplement for systems that were not designed to handle high-moisture corn.
The drying rate of corn depends on two things — the moisture content of the grain and the economics of it, says Sumner. “If moisture content goes down closer to 15 percent, it costs less. But it’s cheaper per point the more moisture you remove. Those last few points you’re trying to remove from the grain are the hardest to remove cost-wise.
“Looking at drying temperatures, for high-quality feed, it’ll probably be about 140 degrees, with the grain itself not exceeding that temperature. You can get it up to 160 degrees, but once you get above that, the kernel will crack. When it cracks and if moisture gets in the bin, you’ll have aflatoxin and other problems,” he says.
The humidity in the air is another factor in drying, says Sumner. “During harvest, the humidity in the air is usually high. The higher the humidity of the air you’re heating, the less water-holding capacity the air will have. Hopefully, we can do the majority of our drying through the middle of the day when humidity is the lowest. But you won’t always have that luxury — you’ll have to dry at night and early in the morning.”
The volume of the air you use to dry grain depends on the fan you’re using and the depth of the grain you’re drying, he says. “The more air, the faster it dries. The less air, the less the fuel costs will be. You have to try and hit that happy medium.”
With in-bin drying, a grower can take 3 to 6 feet of grain, put it in the bin, and turn on a dryer that has the capacity to dry, says Sumner. “I’m not talking about an aeration fan but a dryer fan. It takes six to 12 hours. Then you put another air layer on top of that and create a drying zone up through the grain. The grain below is dry and what’s on top is wet.”
The problem comes, he says, once you fill the grain bin. “The grain on the bottom of the bin gets really dry — below 10 to 12 percent. That is a problem whenever we market that grain. Twelve-percent grain will bring more money than 10-percent grain. We can sell corn from 12 to 15 percent. The other problem is that as you add grain, it has to be thinner and thinner. The air flow goes up through the grain, and as you get a higher column of grain, it takes more energy or effort to blow the moisture off with heated air.”
Batch-in-bin drying, says Sumner, is when you have a bin set up as a dryer. With this method, a 2 to 4-foot layer of grain is placed in a drying bin. The layer (batch) is rapidly dried and then cooled and removed.
“Once you move the grain down to 15 or 17-percent moisture, you transfer it to another bin. If you move it at 17 percent, put it in another bin, and don’t put any air to it immediately, that’s called ‘steeping,’ and you can probably move another point or two by doing that. Then, put the air to it. If we don’t aerate this grain, condensation will occur and you have a bigger problem. For this type of system, we’re talking about 40 CFM per square foot at 3 inches static pressure, with heat requirements of 120 to 140 degrees.”
An alternative is the Easy Dry or Top Dry systems, says Sumner. In these systems, the drying floor is in the top of the bin. You put in 2 to 3 feet of grain, dry it down, pull a lever, and it drops into the bottom of the bin. Then you move that grain to another bin. After it drops out, you refill it.
With continuous-flow drying, he explains, grain comes in at the top and goes out the bottom. A thin layer — two thirds to 1.5 feet — moves continuously through the drier, first through a drying section and then through a cooling section. Continuous loading and unloading is required, and fan requirements are 75 to 125 CFM per square foot. Heat requirements also are very high, at 180 to 200 degrees F.
“The grain comes in wet, goes out dry, and it’s running continuously, says Sumner. “The capacity of these can range from 200 to 1,400 bushels per hour. If you’re going to remove 10 to 12 points, that capacity drops lower. As you remove fewer moisture points, your capacity increases with these systems. These dryers have automatic controls, but it’s very important that you learn how to use them.”
When selecting drying equipment, it’s important to match your dryer to the harvest rate and how long it will take that grain to dry, he says.
“You also want the capability of drying multiple grains — not only corn but maybe beans and wheat. The air-flow rate needs to be sufficient to match the harvest rate and to have sufficient heat. As the grain gets deeper, it’ll take more energy to move the air. As the depth of grain increases, your air flow decreases.”
Peanut drying equipment also can be used for drying corn, says Sumner. “There are several sizes and capacities out there, from 14 to 28-foot trailers. There are also semi-trailers, and all have been designed for drying peanuts with a particular fan. Your operation may be designed for one type of trailer, or you may have from a 12 to a 21 or 28-foot trailer. The air flow ranges with these types of units, from 50 to 100 CFM per square foot. That’s based on 2 feet of grain in the trailer.”
One of the big differences between corn and peanuts, he says, is the density. “We can round up a peanut wagon with peanuts and not worry about overloading it. But if you round up a peanut wagon with corn in it, it might not make it down the road — it could fold in half on you. Keep that in mind — if you’re going to use these units, even just to transport grain, make sure your labor understands that the wagon cannot be filled to capacity or you might not have them for harvesting peanuts.”
The burners in peanut wagons have been designed mainly for 95 to 105-degree air, says Sumner.
“You don’t want the drying air for peanuts to get any higher because it will cause splitting of the kernels. These burners probably can give you a 50 to 70-degree rise in temperature. That means if its 70 degrees outside, you might get from 120 to 140 degrees air temperature out of it. You’re limited by that — you can’t put a peanut dryer on your peanut wagon, with corn in it, and be able to turn it up to 160 degrees. The thermostat on that dryer probably only goes to 140 degrees maximum and some only go to 120. It that’s the case and you think you can get 140 degrees from it, you’ll have to replace the thermostat.”
There are peanut dryers that have been designed for peanuts and grain, and they have a larger burner capacity, he says.
“In the past few years, we’ve seen more semi-trailers being used for peanuts. They were designed — from an air-flow standpoint — for peanuts. But manufacturers of these units have come up with an alternative design for grain. Most are not designed to have shelters built for them. They sit outside, so you have to deal with the rain. They can be used, but it’s important not to go above the grain line.” In a peanut wagon, at a depth of 2 feet, corn capacity will range from 180 up to 580 bushels, so the volume of grain is limited, says Sumner.
“When the air-flow rate is increased, drying time is reduced but fuel usage per bushel will increase because you’re removing the moisture faster. The air capacity will go down if we decrease the depth of the grain.”
If a grower plans to store corn on the farm, he can dry down to 15-percent moisture and start aerating, he says. “For short-term storage, you can get by with 15. If you store for longer than three months, you need to get grain down to 11 or 12 in south Georgia. Three points of moisture equals dollars, and you have to ask yourself if you can make that up on long-term storage.”
Shrink will also be a factor in storing corn, he says. “If you put in 1,000 bushels at the end of harvest, you won’t pull out 1,000 bushels six months later. Shrinkage will occur, and there will be less grain.”
Some farmers, says Sumner, are considering temporary grain storage. “Out in the Midwest and in the northern U.S., they do a lot of this. Flat storage is a possibility, where you put up a 4 or 6-foot wall and put grain in it. One thing to keep in mind if you’re going to build something is that you have a lot of sidewall pressure with corn. As the depth of the corn increases, more lateral pressure is placed on the sidewall.
“The other factor in flat storage is that you need aeration. It’s no different from putting cotton seed in flat storage. Basically, if you’re going to move grain, you need to aerate it after moving it. If you dry it in another facility and move it to flat storage, you need to aerate it. If you don’t aerate corn, moisture will condensate and cause problems.” e-mail: [email protected]