| 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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