Harvesting

Tall varieties are usually ready for harvesting approximately 120-160 days, and short types 90-120 days, after planting, the variation being mainly due to the variety used and seasonal effects, especially temperature and availability of soil moisture. Evenness of growth, ripening and moderate height are essential requirements for successful mechancial harvesting, particularly combine harvesting.

• For this reason alone it is essential to obtain seed of a known variety, grown by reputable seed men.
• Unselected seed produces plants which ripen over a prolonged period, or grow unevenly with varying size, all of which make mechanical harvesting extremely difficult and costly.
• Leaving mature plants standing in the field because many others are unripe also increases bird damage, which is a major cause of seed loss in many temperate and tropical countries.
• Delayed harvesting also allows unwelcome changes in seed-oil composition, for once the plants are physiologically mature, i.e. when the seed yield and oil content are highest, free fatty acids increase.
• Selective manual harvesting is usually possible only on small holder crops unless labour is cheap and plentiful, or to provide employment when other work is scarce.
• Where labour is available, plants can be cut and kept in the field until dry, then threshed by a harvester moving from stalk to stalk.
• The heads are cut from the plants and thrown into the tray of the machine, from which the cutter-bar and reel have been removed.
• Alternatively, the heads are cut from the plants, the stem is lopped about 1 cm from the ground and the heads spiked on the stems, seeds facing down, to dry.
• Seed heads can also be threshed with modified hand or mechanically powered maize shellers provided these are accurately adjusted, operations which also provide employment.
• Seed is ready to harvest when the back of the flower heads turns yellow or brown, and seed moisture content is 10-12 per cent.
• They can then be threshed directly by combine, or thrown into a harvester as described previously.
• This system, while it may increase harvesting costs, substitutes for an even stand, and allows a combine harvester to work within acceptable height limits in tall varieties without a major increase in vegetable matter throughout.
• Chemical defoliation or desiccation using di quat, magnesium chlorate or di pyridyl phosphate can accelerate drying of standing crops and materially assist combining operations.
• Seed-oil content of defoliated plants is similar to those untreated and germination is unaffected when this operation is correctly timed, i.e. when seed moisture content is approximately 35-40 per cent.
• If carried out too early there is loss of yield, oil content and oil quality.
• Grain combines can be fairly easily adapted to harvest or thresh sunflowers using attachments supplied by makers, or specialized manufacturers.
• Head snatcher considerably reduces green material reaching the drum, and allows a lower setting of the cutter-bar.
• Accurate fitting and operating is essential, since losses at the cutter-bar resulting from in efficient use or unsuitable equipment can easily reach 10 per cent of the crop.
• Modifications may also be necessary to screens and straw walkers to avoid blockages and risk of fire.
• Provided recommended speed, drum setting, and attachments are used, direct combining of sunflower requires no special skill.
• It is , however, essential to relate the forward speed of the machine accurately to each crop, often to individual fields.
• Settings will usually vary during the day, and almost certainly with different varieties.
• Fast speeds also overload elevators and the threshing drum.
• Crops grown for seed must be handled with much greater care than commercial crops, since even minor seed-coat damage will reduce germination by 25 per cent.
• In India majority of farmers adopting the local methods of harvesting, threshing.
• After full maturity of grain only the flowers are to be harvested.
• Seed is ready to harvest when the lack or the flower heads turns yellow or brown.
• Normally all flowers will not mature at a time, hence, matured flowers can be harvested at different periods.
• The harvests flowers should not be kept in heaps since the seed will be spoiled because of high moisture in the seed and heat generated in the heap.
• After thorough during for 2-3 days the grain is seperated from flowers by beating with slicks or rub against rough and hard surface.
• If the grain is for seed purpose. The selected flowers are rubbed over a gunny bag surface.
• The moisture in the seed should not exceed 8-10% at the time of storage.
• Seed can be stored in well aerated bags. Properly stored seed will have the viability upto one year.
• Recently several types of mechanical threshers are available for separate up the seed from the flower and it is labour saving and economical.

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Threshing

Threshing of seed heads is an important unit operation which consists to two steps: Dislodging of the seeds from the ear head and Separation of seeds from florets, chaffy and other plant materials.

The methods in vogue for threshing sunflower are;

(a) beating the seed heads with flails and winnowing the seeds,
(b) moving wire mesh netting,
(c) spreading seed heads on the floor, rolling on them stone rollers drawn by bullocks and winnowing the seeds,
(d) using rasp bar type grain threshers or maize sheller after some modification in these equipment.

The threshing by rasp bar type thresher gives maximum outturn of 342 kg/h with a threshing efficiency of 98% and is more economical compared to disc thresher or hand threshing. However, disc and hand threshing may be used by small and medium farmers and the threshed seed may be used for breeder seeds because of very low (1.5%) breakage and high germination (88% to 89%).

• The dried heads are beaten with the help of wooden or bamboo stick to separate out the grains
• The commercial crop may be threshed with available threshers by reducing their speed.
• The plants should be removed from field and used as fuel.
• Threshed seed should be cleaned as soon as possible and dried to less than 10 per cent moisture content or oil quality will suffer.
• In hot countries, standing sacks with the necks open preferably under shade is usually sufficient to dry seeds quickly.
• Artificial drying may be necessary and cold air quite effective in most instances.
• Threshed sunflower heads are usually burnt or ploughed in after harvest, but are occasionally ground and fed to stock.
• Their feed value is limited since they tend to be unpalatable.

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Cleaning And Grading

• The pedal-cum-power operated air screen grain cleaners are used for cleaning of oilseeds with sieves of 8mm for scalper and 3mm for grader can be used for sunflower with a capacity of 280-350 kg/h and 91-96% purity.

Decortication

• Hull content of sunflower seeds varies between 30-40% depending on the variety.
• Its hull mostly contains crude fiber and insignificant quantity of fat.
• It is usually removed before oil extraction otherwise its presence would cause great wear on machinery with higher energy requirement as well as its presence in cake or meal would reduce their biological value.
• Moreover, the hull would reduce the total yield of oil by absorbing and retaining oil in the pressed cake, hence its removal is must.
• Traditionally the hull of sunflower seed is removed by hand. The flattened shape of sunflower seed presents an inherent difficulty for complete dehulling of the seed using a disc hulled as considerable proportion of seed escapes undecorticated.

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Drying

The sunflower seeds are dried below critical moisture content of 7-9%. Oil content has almost no effect on drying rate. Common drying chambers may be used for this purpose at appropriate temperature and for necessary duration of the drying, without violating the internal balance of the seed. The temperature should not be too high and drying could be done by contact, convection or radiation drying.

• In case contact drying is done, the seeds need to be conditioned prior to oil expression.
• A drying air temperature of 1100C or grain temperature of 510C is recommended in case of heated air drying, while a steam temperature of 1300C is recommended at 4-5 kg/cm2 saturated steam pressure in case of steam drying.

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Storage

• After threshing winnowing is done to get clean seed.
• The seeds are dried in sun for 2-3 days to bring down the moisture content to 5.0 percent .
• The seeds are stored in gunny bags , in ware houses with good ventilation.
• There should not be high humidity and moisture inside the storage houses.
• Sunflower seed dries easily, either in-sack or artificially, and once dry i.e. 5.0 percent moisture content, stores well but is susceptible to insects, vermin and other storage pests.
• Storage time for seed with high moisture content is critical; at 25 per cent it is negligible, but at 16-18 per cent should not be more than 50-60 hours.
• On-farm storage must take these factors into account, or losses can be extremely high.
• The author has seen bins of sunflower seed which had not been properly cleaned before filling and not protected by insecticides, literally heaving from the activities of insects and mice.
• Seed with increased phytomelan layer is less susceptible to insect damage in store, as is low oil-content seed.
• Since the seed is bulky,long-term on-farm storage is unprofitable, and seed should be moved as soon as is practicable.
• Storage of sunflower seeds in various structures namely mud bin, coaltar drum bin, black and white polythylene bags have indicated the suitability.
• Seed required for special purposes or breeding, should preferably be stored in metal containers, rather than polythene or paper bags, and placed in cold storage.
• This is especially necessary where there are periods of high temperature combined with high humidity, for in these circumstances viability rapidly diminishes.
• Large seed apparently maintains its viability longer than small seed under all conditions.
• When insecticidal treatment of bulk seed is not possible, or undesirable, forced aeration with cold air can inhibit insect infestation to a considerable degree.
• When hot-air drying is necessary, a temperature above 50 degree celsius tends to reduce viability, but has little effect on seed constituents.
• Too low a temperature increase cost of the operation.
• Germination tests should include an interval corresponding to that when seed is normally sown, since some temperature effects may be long term.
• Higher temperature can be used for seed destined for crushing, and oil produced from seed dried at 80 degree celsius showed no increase in free fatty acid content.

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