If the crop is infested with green weedy material or has a few late set pods that are still green, application of a desiccant will aid combining. As well as increasing production costs there may also be loss of crop from the passage of the sprayer when desiccating. Desiccation will not advance seed maturity and has a slow effect on green stems. It is important to apply the desiccant at the correct stage of maturity. Application before this stage may result in reduced yield or loss of seed quality.?
The most widely used material is diquat. A non-ionic surfactant can be added (but before spraying consult the processor in the case of crops grown for human consumption).?
Moisture content of combining peas seed should have fallen to 40 - 45%. At this stage the seed is mature, and the crop yellow, lowest pods nearly brown and at the dry, "parchment" stage, those higher up being yellow. The seed within the pods should easily detach from their stalks and feel rubbery. If the desiccant is used too early yields may be reduced and quality affected.
?Apply when 90% of field bean pods are dry and black and most of the seed is dry. At this stage most of the leaves have senesced and fallen but the stems are still green. The contact action is fast, and harvesting can be carried out 4-7 days later.
?Glyphosate is not a true desiccant but can be used as a pre-harvest treatment to control perennial weeds. It must not be used on crops destined for seed.
Care should be taken in harvesting peas, and if destined for the packet trade, chip shop or export, value is reduced if pea seed is "bleached" by the sun. Quality can be affected by wet weather at harvest causing staining in a lodged crop. If moisture content is low (~12%, or if they are over-dried), the crop may be unsuitable for human consumption, the percentage of 'non-soakers' increases and the seed may split and crack. Peas for micronising for pet food must also have a good blue/green colour. Yield is lost if peas are left too long in the field and shelling out and pod shatter occurs.
Tips for combining:
Peas can be combined when moisture content of the mature seed is 18% MC, and higher quality seed and human consumption is often achieved by early combining at 18-20% MC followed by careful drying. This avoids damage to the seed coat, and a higher percentage of non-soakers. Do not leave peas in the field until 12% MC. If peas are required for animal feed, they can be combined at moisture content lower than 18% and drying costs are reduced. At low moistures the seed may split, but split peas are still acceptable for animal feed. However, harvesting at such low moisture content may well significantly reduce the recoverable yield due to pod shatter and shelling out. Where possible, crops should be direct combined without pre-harvest desiccation, only practical in a dry harvest, in a weed-free crop that is dying back evenly.
Beans are often perceived as being able to withstand harvest delays long after other crops such as cereals have been harvested. Other operations, including seed bed preparations and oilseed rape sowing, can often take priority over bean harvest.
However, once beans are ready to harvest the quality will begin to deteriorate. If pods split and beans are exposed to light this will cause the seed coat to darken and increase the amount of crop loss during harvesting. When mature, cycles of wet and dry weather increase the chances of staining if they are not harvested. Quality is key to achieve the human consumption premium.
The quality standard for peas and beans is usually 14% moisture content (MC) with 2% impurities, or a combination of the two that should not exceed 16%. Drying can be more difficult with peas and beans than with cereals due to seed size, and while damaged produce is acceptable for compounding, mouldy produce is not. Peas and beans should not be over-dried and at higher temperatures texture may be affected and peas may split.
The large size of bean seeds makes drying difficult as they have a low resistance to air flow. It takes time to move moisture from the inside to the outside hence slow, gentle drying with ambient air is best.
The tables below detail the maximum recommended drying temperatures:
Maximum drying temperatures – Peas
|Product||%MC||Max drying temperature|
|Maximum drying temperatures – Beans
|Product||%MC||Max drying temperature|
|Seed||>24%||34 - 38°C|
|Seed||<24%||38 - 43°C|
|Human consumption||43 - 49°C|
There are several types of dryer that may be used for peas and beans, but those operating at low temperatures are safer.
Floor-ventilated bins are easy and relatively safe to operate. When the initial moisture content is high, the transfer of the produce from bin to bin and the use of warmed air together with adequate ventilation may be necessary to avoid mould developing in the upper layers.
Radially-ventilated bins allow faster drying than floor-ventilated bins, but care must be taken not to overheat peas and beans.
On-floor drying using ambient or warmed air can be used, and provided there is sufficient volume of air?and adequate ventilation, peas of relatively high moisture content can be dried using this method. Care must be taken not to load beans too deep if moisture content is high and if lateral ducts are spaced wider than 1 m.
Continuous flow driers designed to work on a short period/high temperature basis need more careful operation than other systems for peas. Use of continuous flow driers should be avoided where quality is important since they may cause cracking.
For safe storage, the maximum moisture content of peas depends upon the method and the length of time they are to be stored. Peas may be safely stored for up to 4 weeks at 17% MC, but if they are to be stored until the following spring, the moisture content should not be above 15%. If the peas are in bulk with forced ventilation or frequently moved, the moisture content can be 1% higher.
Storage in dark areas is recommended for beans destined for the human consumption market to delay the development of tannins which cause beans to discolour. Beans must be dried down to 14% MC for long-term storage in bulk - this is important since beans are often stored for some time before they are sold.