Chapter 7. Planting, Harvesting, and Curing Peanuts

Factors discussed in earlier chapters, from land preparation to variety selection, have a direct impact on the planting operation. The planter should be selected and prepared to match the production practices to be used.

Planters are designed to perform five major functions: open a furrow, meter seed, place seed, cover the seed, and firm the soil around the seed. No-till planters, in addition to the five functions listed above, must also manage crop residue and prepare the row for planting. Peanuts are a fragile seed compared to corn, soybeans, or cotton. Seed damaged in planting may not germinate. A peanut planter must not only meter and place the seed accurately, it must handle the seed gently to avoid damage.

Planter Types

Two types of planters are available for peanuts: the plate planter and the air planter. Plate planters are divided into two groups based on the design of the plate: horizontal plate or inclined plate. Air planters used for peanuts also fall into two groups: pressure disk and vacuum disk. Air planters that use a seed drum are not recommended for peanuts.

Horizontal plate planters typically have a plate mounted in the bottom of the seed hopper. The plate for peanuts is modified to allow gentle handling of the seed as well as accurate metering. Usually the plate mechanism is an attachment that must be added in the seed hopper. Inclined plate planters may have one or two seed plates per row. The seed plate cells are sized and selected for peanuts and usually do not require modifications or attachments. Planters that have two seed plates per row have a lower plate speed, which provides gentle treatment. Plate planters, horizontal plate or inclined plate, are accurate and effective if properly set up and operated within the manufacturer's recommended ground speed range.

Air planters use a seed disk to meter the seed. The seed disk is mounted vertically in the metering chamber. Cells are cut or formed in the edge of the disk to meter the seed. Air pressure is used to hold the seed in the cells. Pressure disk planters use a fan to blow air into the metering chamber. Vacuum disk planters have a fan designed to remove air from a chamber behind the seed disk. The vacuum created holds seeds from the metering chamber in the disk's cells much like the pressure disk system. The key to accurate planting with an air planter is controlling air pressure or vacuum. If the pressure or vacuum is too strong, too many seeds may be held in the cell. Likewise, if the pressure or vacuum is too weak, the cells may not be properly filled. Brushes remove extra seeds from each cell. As with the plate planters, gentle treatment is important. Seed disks usually have more cells than seed plates, allowing the disk to turn slower. Air planters can maintain metering accuracy at higher ground speeds than plate planters and tolerate a broader range of seed sizes. Refer to the operator's manual for information on setup, operation, and speeds.

Preparing to Plant

Before the planting season, take time to give planting equipment a thorough examination. Look for signs of worn or damaged parts, drive chains, gears, and seed plates or disks. On air planters, look for cracks or leaks in the air tubes. Also check the air delivery on each fan. Make sure the drives are turning freely and lubricated, if required, according to the manufacturer's specifications. Seed plates are usually driven by a press wheel, gauge wheel, or transport wheel. This wheel provides power to turn the plates or disks, and often fertilizer or pesticide applicators as well. If the wheel is inflatable, check the air pressure. A overinflated or underinflated tire can seriously affect planting accuracy.

Be sure to calibrate fertilizer, pesticide, and planting equipment to ensure accuracy. Refer to the operator's manual to find the proper drive setup for your needs. Table 7-1 gives the necessary seed spacings for selected seed populations. Once the planter is set up, check its performance in the field to ensure continued accuracy.

Preparing for Harvest

Successful harvesting begins with proper preseason maintenance of harvesting equipment. Peanut diggers and combines have many key parts that require service for good performance.

On diggers, start with the blades. The edge should be sharp and the blade should not be worn away. As the blade wears it gets narrower and shorter, which means it may not do a good job of lifting the peanuts so the shaker can catch them. The shaker chain or shaker wheels are driven by either PTO or hydraulic power. For PTO-driven units, inspect the driveline carefully for wear or damage. REPLACE ANY MISSING SAFETY SHIELDS! Repair any worn bearings or other parts in the driveline. For hydraulic powered diggers, inspect the hoses for wear or signs of leakage. Replace any damaged hose. Check the hydraulic control valve and the quick connects as well. Check the shaker chain or wheels for signs of wear. Replace any worn or damaged chain links, rattler bars, or kicker wheels. Also inspect the shafts and bearings for wear and replace where necessary. Finally, check the inverter arms. Be sure they are bent to the proper shape. Once your inspection is complete, hook up the digger and run the shaker. Once again, check for any signs of wear or damage in the system.

For peanut combines, start by checking the input driveline for wear in the universal joints and wear or damage to the telescoping tube and the coupler. Check the lubricant in the gearboxes and service as recommended by the manufacturer. Check chain drives for wear and proper tension. Replace any chain or sprocket which does not measure up to specifications. Check belts for wear and proper tension. Replace worn belts and pulleys as necessary. Check the condition of shafts and bearings to be sure they are acceptable. Look inside the combine and check the condition of stripper bars on the cylinders and on the concaves. Replace any broken stripper teeth. Look for clogged or blocked holes in the concaves. If the openings are blocked, peanuts cannot fall through into the cleaning pan. Check shaker pans or cylinders throughout the combine for proper movement or timing. Inspect the stemmer saws for proper alignment. Replace any blades that are broken. Check the condition of the shaker pans, lip screens, or other cleaning elements, and be sure they are set properly. Inspect fan blades for wear and fan housings and conveyor tubes for air leaks. Air leaks can prevent proper cleaning or handling of the peanuts. Look inside the elevator tubes for obstructions. Peanuts will crack if they hit obstructions, resulting in a lower grade. Finally, check the hopper and dump cylinders to be sure they are working.

Refer to the operator’s manual for recommended adjustments and settings. In addition to the recommendations above, give the machine a general inspection to find and repair loose or broken parts. A little time spent in preseason maintenance can save many hours during the harvest season. Above all, observe all safety precautions while servicing or operating the digger or combine!

Digging

Peanuts should be dug when maximum yield and quality can be obtained. The hull-scrape test can help predict the best time to dig. Contact the county Extension center for more information. Pay close attention to the weather when planning digging. If digging and combining are staggered, peanuts won’t be left too long in the windrow.

Once digging begins, keep digging losses to a minimum. Most harvesting losses occur in the digging operation and can be enormous if not carefully managed. Heavy digging losses are unavoidable when pegs are weakened due to over maturity or premature defoliation caused by disease, or when the soil is very dry and hard. Under normal conditions, a yield loss of 5 percent or less should be possible if the digger is adjusted and operated properly.

Reducing Digging Losses. Digging losses are primarily of two types: 1) peanuts that are cut off when the blades are run too shallow, and 2) peanuts that separate from the vines as they are being lifted out of the soil. Additional smaller losses may occur as the plants are being elevated, shaken, and placed in windrows. "Lifting" or reshaking windrows may cause additional peanuts to be lost, but data is not available on amounts. Adjusting the digger for optimum performance requires considerable operator skill. Blades should be sharp and should penetrate to the same depth on heel and toe. A slight forward pitch of the blades will lift the plants and loosen the soil around them, making their removal from the soil less likely to break the pegs. Ideally, the blades should cut the taproot of the plant just below the nuts. In some fields, however, the blades may have to be run deeper in the heavier spots. Adequate but not excessive soil moisture improves digger operations. Changes in soil type or moisture within a field can cause the digger to run deeper or shallower. If the digger runs shallow, peanuts will be lost when the blade cuts them off. Pay close attention to the windrow and look for signs of inadequate depth.

Proper synchronization of ground speed and shaker speed is essential to keep from dragging the plants forward, on the one hand, or snatching them backward out of the soil on the other. The plant should rise vertically and fall back to the ground approximately where it was growing. If the shaker is PTO-driven, and there is a fixed ratio between ground speed and PTO speed in each tractor gear for most tractors. Thus, speed must be synchronized by selecting the proper gear to operate in. Most modern tractors have a sufficient selection of gears to allow synchronization. Some tractors may offer a PTO that is internally synchronized to ground speed. Hydrostatic drive tractors provide infinitely variable ground speed at any given engine speed, making it easier to achieve synchronization. Hydraulically driven diggers can provide a constant shaker speed at any engine speed that provides adequate oil flow in the hydraulic system. Hydraulic diggers can be synchronized more accurately by adjusting the digger control valve. The operator can chose the best gear for the tractor and then synchronize the digger to match it. Even with proper synchronization, ground speeds in excess of 4 miles per hour will tend to jerk the plants from the soil and cause heavy pod losses.

Keep Windrows Loose. Windrows should be loose and fluffy for good drying and should be placed on level ground, or preferably, on a slight ridge for drainage. If flat cultivation was practiced, this will not present a problem. Otherwise, some device like a drag bar or leveler will need to be mounted under the shaker to tear down the row beds and form a slight ridge under the windrow.

Inverters should be adjusted to turn the plants completely upside down so that the peanuts are fully exposed to air and sunlight for fast drying. Peanuts in contact with the ground do not dry as rapidly under normal conditions as those supported off the ground, and they will be much more susceptible to damage during adverse weather conditions. On hot, sunny days, peanuts very close to or in contact with the soil may get too hot and develop off-flavors or poor milling quality.

Reshaking or lifting windows often helps with drying, particularly if the soil was wet at digging or if rain soon after digging stuck the vines to the soil. Careful synchronization of the lifter conveyor with ground speed is necessary. Lifting or reshaking when the vines have become dry and brittle is to be avoided since heavy losses will occur.

Combining

Combining is the culmination of a year's peanut production efforts. As such, it deserves careful assessment to ensure the maximum yield and best quality. Modern combines will get peanuts off the vines under almost any circumstances. Field losses, mechanical injury, germination, and even flavor, however, may be influenced by the feeding rate into the combine, the cylinder speeds and clearances, the cleaning and conveying fan speeds, and the moisture content of both peanuts and vines at picking.

Tests by various researchers have indicated that hull damage, loose shelled kernels, and shelling damage (splitting and skinning) are less for peanuts combined at moisture contents of 25 to 35 percent. However, combining at 20 percent moisture will reduce curing time and costs. During periods of good drying weather, combining can safely be delayed to take advantage of additional infield drying. Vines should be dry enough to break and tear apart readily.

Picking action should be just aggressive enough to remove all the peanuts from the vine with a minimum of vine breakage. Excessive picking action takes more power and breaks the vines into short pieces so that instead of passing out over the vine racks, they fall through with the peanuts and overload the cleaning screens.

Stripper fingers or bars should be adjusted as moisture conditions change during the day. The front strippers are usually set to be more aggressive than those in the rear. Long, clean hay should be discharged from the machine with a minimum of short, broken vines in the hopper.

Cylinder speed should be kept to the manufacturer's recommendation or below and never more than is required to get the peanuts off the vines. Slow cylinder speeds are especially important when combining seed peanuts. Some cylinder speeds are adjustable independently of tractor engine rpm; on others, the speed is regulated by the tractor throttle and is generally correct when the tractor PTO is operating at rated PTO speed or the PTO speed recommended by the combine manufacturer.

Keep tractor engine speed near the recommended level in order for the cleaning and conveying components of the combine to work properly.

Watch Air Velocity. Air conveyors on the combine can cause considerable hull cracking if the fans are operated too fast or the dampers are not adjusted properly. Use only enough air velocity to lift the peanuts into the bin. The air velocity for the cleaning screens also requires frequent checking and adjustment. Sufficient air should be supplied to blow sticks, trash, and "pops", but not marketable peanuts out of the machine. If the screens become heavily loaded with trash, it may not be possible to get good separation. Consequently, either good peanuts will be blown out or trash will go into the bin. Overloading of the screens may indicate that picking action is too aggressive. Tail board adjustment also affects what is blown out of the back for any given fan setting.

Proper synchronization of the combine pickup with forward speed is important to minimize field loss of peanuts. The windrow should flow evenly and smoothly into the combine, without being pulled apart by a ground speed that is too slow or pushed ahead by a ground speed that is too fast. Either situation will cause peanuts to be lost off the vines before getting into the combine. Some combines have an adjustment to quickly change pickup reel speed; on others, a sprocket must be changed. In either case, changing gears on the tractor will affect synchronization and reel speed should be adjusted. The pickup tires should run just above the ground surface. If they are allowed to dig into the ground, they will pick up dirt and carry it in with the peanuts.

Combine pickup and cleaning losses (peanuts picked but blown out) can be appreciable. However, proper adjustment and operation of the equipment can virtually eliminate these losses.

Harvest Safely

Always remember: tractors, diggers, and combines are potentially dangerous pieces of equipment. There are many moving parts, not all of which can be completely shielded. Always disengage power before making adjustments. Never allow bystanders or riders near the combine when it is in operation. Keep all protective shields and guards in place. Above all, be alert and on the lookout for hazardous situations. Read the operator's manual and observe all safety precautions. Learn to recognize and avoid hazards. Contact the county Extension center for recommendations on improving safety in farm operations.

Efficient operation of the peanut curing system involves: 1) cleaning and repairing the equipment before harvest, 2) windrow curing the peanuts as long as practical, and 3) operating the equipment properly.

Preseason Operation

The preseason cleaning and repairing of the curing trailer, plenums and canvas connectors, and the fan and heater can pay big dividends. Dirt and old crop residue under the trailer curing floor and in the trailer plenum chamber can block air flow and contaminate the new peanuts with aflatoxin. The best way to clean the curing trailers is to remove the floor assembly and flush out the trailer with a stream of high-pressure water.

Clean leaves or trash from the fan and plenum. These can be a fire hazard when the burner is operating. Cut any grass and weeds that could restrict the air inlet to the fan. Remove all trash that could restrict air flow to the fan screen. Clean the dirt and trash off the fan blades to reduce drag.

Make sure that the LP gas line from the tank to the burner is in good condition and not damaged. Most peanut fans have a ring-type heater with many holes for gas-air mixture. Clean these burner holes to ensure good ignition and an even flame all the way around the burner. If some of the holes are plugged or partially closed, too little gas-air mixture may exit for good ignition or proper burning, which will waste fuel.

Check all electrical wiring, fuses, breakers, and controls. Make sure they are properly installed and functional. Have an electrician make upgrades or repairs.

Check the main air plenum, canvas connections, and the trailer air plenum for holes and leaks. Be sure to repair all leaks to conserve energy. Air leaks waste energy and increase the curing time. A crack or hole measuring only 1 inch by 24 inches will leak approximately 350 cubic feet per minute on a typical curing system. An extra gallon of LP gas will be required to heat the air leaking from this crack every 11 hours when the burner is raising the temperature 20 degrees, and the leak will also slightly lengthen the curing time. Before you begin harvesting peanuts, operate the fan and heater for about 30 minutes to make sure they are functioning properly. Also, while the fan and heater are operating, turn the thermostat and humidistat up and down to make sure that they are functioning properly.

Refer to the owner's manual for further recommendations on adjustments and maintenance of the curing equipment.

Windrow Drying

The cost of curing peanuts is greatly influenced by the time they remain in the windrow. The longer they remain in the windrow, the more the peanuts cure (dry), and the lower the curing fuel cost; however, windrow losses may begin to increase 3 to 5 days after digging and inverting the peanuts. Even though windrow losses may increase when the peanuts remain in the windrow too long, especially in bad weather, curing costs will decrease as the peanut continues to dry in the windrow. The most economical time to combine the peanuts is when the curing cost savings from windrow drying equals the lost value of the additional peanut losses from windrow drying. As the cost of curing fuel increases, the time in the windrow must increase to achieve the maximum profit.

Curing Operations

Air Flow. To properly cure peanuts, maintain sufficient air flow and proper temperature. If air flow rates are too low, the peanuts will mold. If the air flow is excessive, the energy costs will be high. The recommended air flow rates were established to prevent mold development during curing; however, they have also proven to be the most economical. The general recommended air flow of 50 cubic feet per minute per square foot of curing floor (cfm/sq ft) at 0.75 inch static pressure is sufficient to cure up to 25 percent moisture peanuts 5 feet deep. The air flow provides 10 cubic feet per minute per cubic foot of peanuts at a depth of 5 feet.

Once the fan is selected, air flow adjustments must be made by varying the curing depth or by not using all of the trailers for the system. For example, filling all the trailers half full will result in a higher air flow than completely filling half the trailers. When filling the trailer, be sure to level the peanuts to ensure uniform air flow. Avoid overfilling the trailer.

The minimum or desired air flow rates along with the maximum curing depth using the recommended curing fan is shown in Table 7-2.

Heat. To maintain good flavor and milling quality in the peanuts, maintain the proper curing temperature. If the curing temperature is too high, the peanuts will split when shelled and may also develop a bad flavor. Never allow temperature to exceed 95^o F. The recommended temperatures can be controlled by manually adjusting the heat or using a modulating thermostat, or by using a humidistat and an on-off thermostat. When using manual heat control, adjust the LP gas pressure to achieve the desired temperature rise or curing temperature. Most fan and burner units have a gas pressure versus heat chart. This chart usually shows the British Thermal Units (BTU) output for various gas pressures. If your burner has a "high" and "low" pressure heat value, be sure to use the low position for peanuts. The following formula is a useful aid in adjusting the heat input.

When using an on-off thermostat and a humidistat, adjust the temperature rise to approximately 15 to 20 degrees to reduce the cycling of the burner flame early in the season when the weather is warm. The temperature rise can be increased late in the season when the nights get cold as shown in Table 7-3.

The best temperature controller is a modulating thermostat, which varies the temperature by raising and lowering the firing rate (flame size) without cycling when the weather changes. A modulating thermostat should be set on approximately 75° F if a constant temperature is desired; however, adjusting the setting for the weather conditions as shown in Table 7-3 is preferred.

Steps to Increase Curing Efficiency. When the hulls are wet the drying efficiency is very high. After hulls are dry, especially during the last half of the curing cycle, the drying efficiency will decrease. Therefore, you need a higher air flow for the first half of curing than during the second half of the curing cycle. The air flow can be reduced during the last part of the curing cycle on a multiple trailer plenum system by partially closing the air gates of the trailers during the last half of the curing period. Generally, having the air gate half open is sufficient to keep the curing efficiency high during the final curing stage. By reducing the air flow to some trailers in the final curing stages, the other trailers in the first curing stages containing peanuts with wet hulls will receive an increased air flow. Do not partially close enough air gates to restrict the fan or to cause the heater to malfunction.

On many curing systems, the trailer nearest the fan receives the least air. On these systems, the adjustments can be made by starting the newly filled trailers on the furthest end from the fan until the hulls are dry, and then moving this trailer to the other end of the plenum nearest the fan.

Another way to adjust air flow is to fill the peanut trailers only half full for the first half of the curing cycle to dry the hulls, then dump and mix two trailers into one trailer for the final half of the curing cycle. This method is more desirable than adjusting the air gates if dumping and handling facilities are available. The dumping and reloading of the peanuts will remove some dirt and mix the bottom layer of peanuts with the top layer resulting in a more uniform final moisture content.

Another way to save on heat energy cost and possibly improve curing quality is to recirculate part of the curing air to maintain an ideal curing temperature and relative humidity. This will require equipment changes or a specially designed curing building for the trailer and fans. Research indicates that 40 to 50 percent savings in energy consumption can be obtained using the recirculating systems compared to the conventional systems. A key advantage of the recirculating systems is that if the wagons leak air, the air goes back into the building and is recirculated--not lost to the outside. The economics of converting to a recirculating system will depend on the cost of the changes required and current energy cost.

Some growers have expressed interest in applying "precision agriculture" techniques to peanuts. Precision agriculture is a management system where the grower uses information and technology to optimize crop yields. There are three major components to a comprehensive precision agriculture system: precision production equipment, site-specific farming, and computer controls. Growers can adopt a complete package or choose only the components that suit for them.

Precision production equipment includes planters and chemical application equipment. The choice involves choosing the equipment that offers the grower the best accuracy and control. For example, planters should be selected that allow the farmer to most accurately control seed population and seed spacing. Sprayers and spreaders should be chosen that ensure the correct rate of chemical is applied to the crop. Application errors should be kept to a minimum. In many cases, the equipment currently in use is capable of high accuracy. The grower must take the extra steps necessary, through maintenance, calibration, and adjustment, to ensure accuracy is achieved.

The second phase, site-specific farming, will not be practical unless precision production equipment is in place. To use site-specific farming, maps are produced for each field and the field is divided into smaller sections or grids. Data is collected for each section and the location of the section is recorded by a computer. The computer receives location information from the Global Positioning System (GPS), a system of navigation satellites and radio beacons that can determine position in a field within a few feet. The data recorded for each section can include soil sample information, yield data, weed or pest populations, or any other type of information the grower wishes to manage. Yield monitors for peanuts are now available.

Information from the maps can be used to make decisions about crop inputs like lime, fertilizer, pesticides, or plant population. Growers can ensure that each section of the field receives the type and amount of crop input best suited to that location. Equipment is available which can read the maps and vary the rate of application of lime, fertilizer, or pesticides by location as the equipment moves across the field. The result is each grid of the field receives the right amount of inputs for optimum production and soil conditions are neither depleted or over supplied. Over and under application is virtually eliminated, which can reduce production costs, optimize profit, and contribute to sustainable agriculture.

The third component of precision agriculture, computer controls, applies to curing. Relatively inexpensive controls can be used to monitor the curing process and maintain the best environment for quality. Problems with high temperatures and poor humidity control can be reduced.

Precision agriculture, like most management systems, has some limitations and problems that must be overcome. Applications for peanut production are just beginning to be researched and developed. Before launching into a system, compare the options and alternatives carefully.

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.