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Pea Harvesting

Pre-Harvest Considerations

Depending on type and variety, seeding date and seasonal moisture, field pea crops require a growing season of approximately 90 to 105 days. Pea harvesting must be considered in terms of an overall harvest system. Paying close attention to crop and equipment needs will usually result in earlier harvesting, higher quality and optimum yields. Pay particular attention to:

  • equipment readiness
  • pre-harvest field monitoring
  • proper storage of the final product

All necessary equipment modifications should be made well before harvest time. Desiccation or swathing can start when seed moisture content has reached approximately 25 to 30 per cent. Drydown of the sprayed crop to 16 to 18 per cent seed moisture normally takes five to seven days, depending on weather. Once the crop is combined, a short time in an aeration bin may be required if the grain is not at storable 16 per cent or if the grain is warm. If the crop is to be straight combined, you can begin when seed moisture content has reached approximately 18 to 20 per cent, provided the straw is dry enough to feed through the combine. Aeration of straight-harvested pea is generally required to condition the grain for longer storage.

Field Monitoring

Pre-harvest field monitoring will help determine which harvest system to consider, if more than one is available, and will greatly assist in determining when to begin harvest operations. Monitoring pea fields means checking plants in numerous locations for uniformity of stages of maturity. Most fields will not be 100 per cent uniform in topography – there could be greener conditions in lower, wetter areas and further advanced plants on higher areas. Therefore, a decision to begin harvest will hinge on a majority of the field meeting certain criteria. Do not sacrifice the quantity and quality of your crop waiting for smaller greener areas to reach the proper stage to start harvest.

The decision to start the harvest process will depend on three factors:

  • crop maturity (stage of uniformity)
  • seed moisture content
  • presence of weed growth

Crop Maturity

  • field pea plants mature from the bottom to the top – when monitoring a pea crop, look for a large majority of plants that have tan pods on the bottom, yellow to tan pods in the middle area and yellow green pods on the top
  • seeds in bottom pods will be very firm and require some force to dent the seed coat with a fingernail
  • seeds from middle pods will flatten somewhat with pressure between the thumb and finger, and the seed coat will dent with a little fingernail pressure
  • seeds from the uppermost pods will be fairly soft and, with a little pressure, will split into two cotyledons

Seed Moisture Content

  • seed moisture content of physiologically mature pea will decrease quickly if weather conditions are warm and dry and if humidity is low
  • drought stress in the crop will also result in rapid drydown

Presence of Weed Growth

  • waiting for green weed growth to drydown will jeopardize quality and yields
  • swathed green weeds are unlikely to dry sufficiently in a few days, so combining will be delayed
  • green weed material in a straight-cut operation will cause extra wetness in the threshing areas of the combine, resulting in moisture on the seed coat and dirt adhering to this moisture (earth tag)
  • grades will be lowered because of earth tag

Pre-Harvest Questions

Before harvesting, ask yourself the following questions:

  • does the value of the crop dictate whether a desiccant is used?
  • what machinery is available for harvest?
  • should additional resources be secured?
  • how will the harvested grain be marketed: human edible, livestock feed or seed?
  • how variable is the crop’s maturity?
  • any other variability of crop readiness in the field?
  • what are the current weather patterns?

Harvest Timing & Systems

Timely harvest of a pea crop is critical:

  • harvesting too early will result in immature seeds – this is especially important with yellow cotyledon varieties because immature yellow-green seeds will result in downgrading
  • harvesting too late when the pods are dry and brittle may result in shatter losses and will increase the risk of poorer quality seed due to adverse weather – for green pea varieties, harvesting even several days later may result in excess bleach
  • The method or type of harvest to be used must be decided well before maturity advances and shattering begins. Field pea can be harvested with a number of different systems. The system used will depend on equipment availability, crop condition and weather conditions.

Pea plants mature from the bottom to the top, and are near maturity when the bottom 30 per cent of pods are ripe, the middle 40 per cent of pods and vines are yellow-coloured, and the upper 30 per cent of pods are turning yellow. This is the stage to swath or desiccate if either of these harvest methods is chosen. Harvesting too soon will result in immature seeds in the sample and can cause downgrading. Waiting too long can result in excess shattering and increase the chance of weathering damage.

The most important grading factor for the human market in green cotyledon pea is seed colour. The maximum allowable bleach level for green pea destined for human consumption is two per cent. Green varieties are susceptible to bleaching as they near maturity. Bleaching of seed is caused by high humidity, bright sunshine and warm temperatures. For this reason, extra care should be taken to harvest green pea varieties as soon as possible. In green pea, the vein pattern in the upper-most pods should be easily recognizable and 75 to 90 per cent of the pods should have turned to yellow tan.

Pea can also be left to straight cut without desiccation. Pea crops are mature when seeds in the bottom pods are detached and loose in the pods and when the upper pods are turning yellow. Once the crop is mature it can dry down very quickly if the weather is warm and dry.

Care should be taken when harvesting pea for human consumption. Pea seed samples containing excessive amounts of foreign material or seeds that are cracked, peeled or discoloured are suitable only for the feed market. Soil adhered to the seed is called earth tag and is a common factor in downgrading dry pea. Earth tag may occur during combining when moisture from weeds or heavy dew causes soil or dust to stick to the seed.

Swathing

Swathing can be done when most of the vines and pods have turned to a yellow-tan colour, and seeds are difficult to dent with a thumbnail. As much as one-third of the vines and pods may still have some lime green colour left, but these plants will cure in the swath. The fully formed but immature seeds will dry without much shrinking – the overall seed moisture content will be approximately 25 per cent.

These swathing tips will aid in the best harvest conditions:

  • lower areas of the field (which remain green) should be ignored when the proper swathing or straight cutting time approaches for most of the field – delayed cutting to allow these areas to advance in maturity may jeopardize quality and quantity of the remainder of the crop
  • swath rolling may be necessary to protect the swath from wind damage if the swather lays a dense narrow swath. A very mature dry crop may result in a fluffy swath, prone to wind damage (rolling drier pea swaths will result in greater seed shattering in the swath)
  • lay a wide, shallow swath that will cure and dry quickly – adjust the discharge opening of the swather to as wide as possible to lay a wide swath (avoid piling the swath in bunches)
  • the combine should follow closely behind the swather, if the crop is to be swathed when it is fully mature
  • swathing should be done during periods of higher humidity to prevent shatter losses
  • pea crops that are very short and have many pods close to the ground are usually best swathed when partially green – the pick-up reel will have more material to work with, resulting in a better swath
  • a heavy, taller crop can best be handled with a narrow swather table or by taking a narrow cut (12 ft. to 15 ft.) with a wider table
  • match swath size and density to the combine capacity so that a uniform feed is achieved
  • all varieties of field pea have hollow, weak stems and most will lay over or lodge when heavy in pod – the best method of swathing or straight cutting a lodged pea crop is at a right angle to the direction in which the crop is lying
  • swath the crop slowly – for example 3 to 4 mph (as slowly as it takes to lay an even, uniform swath)
  • swathers should be equipped with a pick-up reel, preferably with stiff fingers, and with vine lifters – adjustment of the pick-up reel, backward or forward, may alleviate piling problems
  • many types of vine lifters are available, and most allow for some adjustment to perform well on all headers – lifters should be spaced every 12 in. on the header for most pea crops but may have to be spaced as close as 6 in. for short, thin crops (for extremely short crops, lifters may have to be removed to get the cutter bar below the lowest pod)
  • swather tables should be fairly narrow, so the table will follow ground contours as the crop is cut close to the soil surface – a narrow table will also produce a more shallow swath (there is usually very little stubble to keep the swath off the soil surface, so rapid drying is important)
  • gauge wheels mounted on the swather table will also aid swather operations – gauge wheels help prevent the cutter bar from digging into the soil and maintain uniform cutting height with less operator fatigue
  • swather tables with adjustable pitch should be adjusted to a steep pitch – this angle will help get the cutter bar closer to the ground and will allow the crop to come off the draper more evenly

Combining

Field pea can be successfully combined as soon as the seed moisture content is down to 20 per cent or less. Seed damage will increase as the crop becomes drier than 16 per cent. This damage reduces both germination and quality.

  • pea vines that are damp or slightly green will greatly increase combine power requirements and may result in plugging and wrapping problems
  • combining at too high a moisture content (over 20 per cent) will increase the amount of earth tag on the pea seed (earth tagging may also occur when combining starts too early in the morning or continues too late in the evening and when dew is present; earth tagging is also common when weeds like thistle or quack grass are present)
  • combining at too low a moisture content will cause excessive cracking and splitting losses – cracked and split seed downgrades quality when pea is destined for the seed or human consumption market
  • keep the combine operating at full capacity to help reduce seed damage in the cylinder and also in the grain elevators
  • combine hoppers should be unloaded at slow speeds to reduce seed damage

General recommendations for combine settings include:

  • low cylinder speed
  • ample concave clearance
  • maximum wind velocity

Swathed Field Pea

Picking up a well-formed pea swath is generally not a problem. Combining is easiest if the width of swather cut is well-matched with combine capacity and the moisture content of the crop is between 16 and 20 per cent. These conditions require the least combine power, and good separation takes place readily.

  • pick-up speed should be carefully matched to the combine ground speed to minimize shatter losses
  • if the combine is equipped with a variable speed pick-up, the proper feeding rate of the swath is much easier to maintain
  • sprocket change on the pick-up drive may be needed to reduce the pick-up speed to that suited for pea swaths

Direct Combining

Field pea can either be straight combined with a standard type cutter bar, a floating cutter bar or with a special pick-up attachment (example is Honey-Bee header).

  • if using a special pick-up, the crop should be uniformly dry to the soil surface
  • a pick-up reel and lifters on the knife guards will usually be required for both standard and floating cutter bars
  • flexible lifters are preferred over the more aggressive rigid lifters for straight cut headers as they reduce the amount of dirt entering the combine
  • proper header height control is important to avoid picking up dirt, which will cause earth tag (earth tag is not easily removed from pea seed and will usually lower the grade of the grain)

Stripper Header

This is the newest header type for straight combining pea crops. It incorporates a flail type cylinder enclosed in a shroud and is operated at 1 in. to 2 in. above the soil surface. One advantage to the stripper header is its ability to harvest badly lodged pea crops.

  • careful adjustment and maintenance of the stripper header is needed to offer a clean undercarriage to eliminate hang-ups of pea vine and dirt entering the combine
  • some concern exists that operating the machine at very high RPMs in dry pea crops will increase the damage to the seed and increase the amounts of split pea and dockage
  • the stripper header width should be properly matched to the combine capacity to both increase efficiency and not overload the combine

Special Pick-Ups/Direct Combining

Another method for direct combining a pea crop is to use a special pick-up (manufactured by Sund or Rake-Up), which pulls the standing, very mature dry pea crop into the combine.

  • pick-up wheels may be replaced with coulters, which cut the pea vines at the edge of the pick-up
  • pea vines must be very dry because this type of pick-up works by breaking plants off at the soil surface before pulling them onto the draper – this operation leaves most of the green weed material standing in the field, and it prevents dirt from entering the combine
  • special pick-ups may not work well in short or thin crops – they perform best on longer pea vines that have fully matured and have been exposed to some rain, as the stems at the soil surface become weak after a rainy period

This type of harvest method is not a feasible option for green pea crops for human consumption markets. Green pea usually bleaches too much by the time the crop is ready for this type of equipment.

Desiccation

Pre-harvest glyphosate should be applied when the crop has 30 per cent or less grain moisture (75 to 80 per cent of pods are tan). This treatment will provide some crop dry down, but this benefit is inconsistent and is unlikely to occur under cool, wet conditions. Apply glyphosate for pre-harvest weed control and not for desiccation. Do not apply glyphosate to pea crops destined for planting seed because irregular germination and seedling development can occur. Applying glyphosate too early can reduce yield and seed size, and may result in levels of glyphosate in the seed that exceed maximum allowable levels.

Chemical desiccation to burn off crop foliage and weeds will reduce the time from maturity to threshing readiness and reduce shatter loss. It will also result in improved quality if the crop is harvested before being exposed to wet weather, compared to a crop left to mature on its own and being subjected to wet weather. Timing of the application is critical because it has immediate dry down effects. Application too early will reduce seed size and yield of pea. The benefits of chemical desiccation is the opportunity to have the crop harvested sooner, reduce risk of exposure to wet weather, and eliminate the risk of swath movement from wind. Standing desiccated crops will also dry more rapidly after a rain, compared to a crop in swath. Germination of seed is not affected unless applied in advance of the recommended stage. If some areas of the field are immature it is better to go around those areas when desiccating if the goal is the highest quality seed production.

Powdery mildew and heavy weed infestations can reduce the effectiveness of the chemicals due to coverage reductions. Chemical desiccation can be very effective for green pea, reducing the time to harvest and resulting in a good green coloured seed. Remember, a desiccant will not assist in maturing immature seed.

  • apply as the crop is approaching physiological maturity – the application can be made when the bottom and mid-area pods have turned tan to yellow colour, and top pods are pitted and starting to turn yellow
  • a desiccant is a contact herbicide, so green material is killed quickly and drydown begins within a very short time – compared to natural drydown, faster (and more even) drydown can be achieved late in the season when days are shorter and generally cooler
  • apply the desiccant at the same time as the proper swathing stage, wait approximately five to seven days, then straight combine or swath and follow immediately with the combine
  • the use of a desiccant will usually eliminate the need for swathing, thus avoiding potential problems with wind blown swaths, rain soaked swaths and pick-up losses
  • spray only as many acres at one time as can be combined in two or three days after drydown – if the entire crop will take more than two or three days to combine, stagger the desiccant application so that not all the crop is ready at the same time
  • use proper rates, high water volume and spray at the correct crop stage

Post Maturity Pre-Harvest Aids (Glyphosate)

Pre-harvest treatment involves spraying the field with ground equipment when pea seed moisture content is 25-30 per cent or lower.

  • the crop and in-crop weeds must have enough green material remaining at application time for the herbicide to be effective
  • glyphosate, a systemic herbicide, will kill and drydown all green growth in approximately 14 to 21 days and will allow for a straight cut operation or swathing and combining immediately
  • this herbicide is not registered for pea crops used for seed purposes

Pea Straw Management

One of the benefits from growing a pea crop is the positive effect of pea residue in the soil. Improved soil structure, tilth and recycled nitrogen for succeeding crops are all benefits of pea straw incorporation. In fact, most of the nitrogen returned to the soil after growing a pea crop comes from the straw. Because of these benefits, it is recommended that pea straw remain on the field and not be baled off for feed purposes. Be aware of the following:

  • dry pea straw breaks up and pulverizes quite readily when combined
  • straw that is slightly green or tough will remain almost whole going through the combine
  • a good straw chopper and chaff spreader will cut and spread the straw and chaff sufficiently so that tillage or direct seeding is not a problem
  • tough straw will wrap around the chopper drum if the straw chopper knives are dull and worn

Storage

Proper field pea storage management is important to prevent a grade decrease.

Drying or aerating down to 16% moisture should be done gradually at temperatures at or below 45 degrees Celsius. If the seed moisture content must be reduced by 5 per cent or more, drying should take place in two stages. With a hot air dryer, pea seeds should be dried to within 2 per cent of final moisture content and then tempered in an aeration bin for at least six hours. Afterwards, they should be cooled to the outdoor seasonal temperature. The slowness of this process prevents grain cracking.

“Many farmers start combining between 18–20% moisture and then truck the product directly from the field to the seed cleaning plant to have their peas cleaned. Usually running the crop through the seed cleaning plant will knock off 1 or 2% moisture. Upon return to the farm, they will stick the field peas in an aeration bin and dry down to 16%. If the combine sample is clean and does not have to move through a seed cleaning plant, farmers will stick the peas directly into an aeration din and dry down to 16%,” says Mark Olson, the Unit Head for Pulse Crops with Alberta Agriculture and Rural Development.

As a rule, grain dryers should not be operated over 45 degrees Celsius to prevent quality losses due to hardening or cracking of seed destined for food use and to prevent germination reduction in seed destined for re-planting. For feed pea, temperatures up to 70 degrees Celsius can be applied. However, Olson points out that field peas are rarely dried through a grain dryer, since this can cause seed damage and also is very noisy.

Field pea can be safely stored at 16% seed moisture content and 15 degrees Celsius for several weeks, but regular bin probing and monitoring is required. Olson also points out it is important to be cautious of weed seed dockage or green materials (i.e. Canada thistle heads) from volunteer crops, as they can cause heating (hot spots) if you cannot not get proper air flow through the bin.