| Arable
Desiccation, harvest, drying and storage of combining peas and field beans
With winter bean harvest now very much in full swing, and with spring bean harvesting in the south only days away, it is timely to focus on the process of harvesting and postharvest drying and storage.
F ield bean desiccation
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. However, if the crop is infested with green weedy material, or has a few late set pods which are still green, application of a desiccant will aid combining. 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. Apply when 90 % of the 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. It can be used on crops for animal feed, human consumption or seed. 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. Field bean harvest
It is tempting to see beans as‘ tough in the field’ and that they will stand 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. While the perception that beans can wait is true to a certain extent, once beans are ready to harvest, the quality will begin to deteriorate. Losses occur as pods open and start to shed seeds, and seed coat colour deteriorates with exposure to the air and light as pods split. Repeated wetting and drying due to rain increase the chances of staining as can combining when the stems are too green.
All of these factors reduce the chances of achieving good visual quality & the premium for human consumption. Equally to leave beans to over-dry in the field can lead to splitting and shattering of the grains in the combine, creating further losses of yield and quality.
12 | Farming Monthly | September 2016
Drying combining peas and field beans
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.
1. 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.
2. Radially-ventilated bins allow faster drying than floor-ventilated bins, but care must be taken not to overheat peas and beans.
3. 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.
4. 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 for beans where quality is important, since they may cause cracking. Storage of combining peas and field beans
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.
Maximimum recommended drying temperatures- Peas
Product % MC Max drying temp Seed > 24 % 37 ° C
Seed < 24 % 43 ° C
Human Consumption
Human Consumption
> 24 % 43 ° C < 24 % 49 ° C
Maximimum recommended drying temperatures- Beans
Product % MC Max drying temp Seed > 24 % 34- 38 ° C
Seed < 24 % 38- 43 ° C
Human Consumption
43- 49 ° C
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