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.
Where possible crops should be direct combined without desiccation in order to reduce costs and the inevitable losses due to sprayer wheelings, losses 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.
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.
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.
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.
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.