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 Desiccation
Timing
Combine
setting
Drying
and storage
Images
Winter beans
are either combined direct with or without desiccation, or can be
combined from the windrow, although the latter is rarely done now,
due to the difficulty of setting a swath up on most stubbles for
efficient combining. In wet weather the crop dries better as a standing
crop.
Desiccation
Where possible crops should be direct combined without desiccation,
to reduce costs and the inevitable losses due to sprayer wheelings,
which can be up to 2.1%, even with 24 metre high clearance sprayers.
Desiccation will not advance seed maturity and is slow to act on
green stems. If however the crop is weed infested or has some small
late set pods desiccation will aid combining. Timing is vital to
maximise yield potential and seed quality. Spray when 90% 0f the
pods are dry and black and most seed is dry (GS 309)
Optimum yield and quality is obtained when 25% or more pods are
black. Diquat (Reglone and other products) is the most common product
used. Formulation is a soluble concentrate containing 200g/l (16.6%w/w)
Diquat as the bromide salt.
Application rate; - 3.0 litres/ha in a minimum of 200 litres of
water
Harvesting can normally be carried out 5-7 days after application.
Possibilities
of early desiccation of beans have long been discussed but little
evidence is available to predict the optimum time for application.
Seed often reaches maximum dry weight well before the foliage has
desiccated naturally. Early desiccation may be feasible for feed
crops however; seed germination and vigour may not be optimised
until after the seeds have reached maximum weight (Figure 19). This
may correspond to varying moisture contents of the seed and in trials,
seed moisture content at maximum seed viability ranged between 30%
and 60%. Thus, desiccation of the foliage and stem once seed is
below 50% moisture content may advance harvest but may not optimise
seed vigour if seed is to be used for seed.
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Figure
1. Seed maturity and quality
in spring beans8
[redrawn from data produced by Pokojska
& Grzelak, 1996. Plant Breeding & Science (40)
11-20]
Click
here for a larger image
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Timing
Winter Beans have the advantage of extending combine usage, as they
are usually ready to harvest 7 to 10 days after wheat. The large
seed is very much slower to dry, compared to small-grained cereals.
The fall in moisture content from 60% to 30% can take 6 weeks compared
with 4 weeks with cereals (Nash, 1977)1.
Because of the crops indeterminate growth habit, uneven ripening
often occurs with the lower pods being over dry and the upper ones
remaining immature at higher moisture content.
Combining is done with moistures in the range 14 to 20%, when all
the pods are dry
and black and the seed hard, ideally with less than 10% of the
stems remaining green.
At low moisture contents shattering can occur. In dry conditions
harvesting is best done early in the morning and late evening to
avoid damage.
Combine
setting
The key point is to reduce pod shatter and damage to the seed.
The combine knife must be well set and sharp, the pick up reel adjusted
for height and speed, to ensure a smooth crop flow. High forward
speed will also help reduce cutterbar losses. Drum speed should
be as low as possible (300 to 500 rpm) coupled with wide concave
clearance, to eliminate splitting and cracking of the crop. Sieve
settings must be wide with maximum fan speed.
Drying
and storage
In the UK beans are normally sold based on a maximum 15% moisture
content and a maximum 2% of impurities, with deductions above these
levels. Most crops will need drying. There are important differences
due to the physical characteristics compared to cereals. Field Beans
being large seeded with a thick seed coat are slow to dry in a bulk-drying
situation. Uneven drying can often occur due to the low resistance
to airflow, particularly with on floor drying systems. The ideal
system being ventilated bin-drying systems. With all systems it
is preferable to preclean as impurities slow down drying. For long
term storage beans must be dried to a maximum of 14% and cooled
to 10oC.
Continuous Flow Driers are also used, but are not ideal, because
of the distance the moisture has to travel from the centre of the
seed; there is a danger of the centre of the seed remaining at high
moisture content. This can result in moulds, which are toxic to
livestock developing in the cracks and a pasty condition to the
meal, which becomes rancid during storage. For seed crops cracking
reduces germination. cracking also reduces premiums over feed for
all quality outlets.
Maximum temperatures:
For seed if below 24% Moisture content: - 43oC
Above 24% moisture content: -38oC
At moisture contents over 20% it is advised to dry twice to avoid
seed cracking and splitting. there should be an appropriate time
interval between the two drying processes.
Standard Conveying equipment may need modification to handle
beans, chain and flight conveyors and augers can sometimes damage
the seed. Bucket elevators often cause problems particularly with
high moisture contents, with the beans trapping and squashing between
the belts and pulleys. the use of "cage pulleys" allows
the beans to fall through without becoming trapped. Both belt conveyors
and pneumatic conveying systems are ideal, provided that the airstream
of the latter is not excessive.
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