Issues to do with soyabean harvesting


THIS series of articles on soyabean is aimed at assisting new farmers who have ventured into soyabean production.
We have followed the cropping cycle from land preparation through planting, weed and pest management up to crop maturity.
We also looked at the role of soyabean in fulfilling the Zimbabwe Agenda for Sustainable Socio-Economic Transformation (Zim-ASSET) goals.
In this article we shall discuss issues to do with harvesting soyabeans.

Crop maturity.
The plants are normally dark green during crop growth.
At maturity, the leaves turn golden yellow and then brown in colour.
Eventually, the leaves drop to the ground forming a thick carpet– good ‘manure’ for the next crop!
If the soyabean is killed by drought then the leaves dry up and shrivel but remain on the plant.
The soyabean pods which at first are green also gradually turn a hairy brown colour.
Depending on variety, some pods turn yellowish, others light brown.
Once leaves start to turn yellow the crop is mature. Mature seeds will be a creamy yellow while immature ones remain green even when dry.

Moisture content of pods.
When dry pods are shaken, a rattling sound is heard from inside the pods.
If the pods do not rattle, the pods are still too wet.
If such plants are harvested, many of the pods fail to split open to release the seeds. The seeds if bagged may turn mouldy.
After leaves fall off, a period of two weeks may pass before the pods are dry enough to harvest.
In some cases, stems can remain green while pods are dry enough to harvest.
Such green stems become a problem for combine harvesting.

Late rains during harvest period
Late rains pause a problem in the harvesting of soyabeans.
They can cause the crop to rot.
It is important to avoid cutting and heaping soyabean plants when there is a chance of rainfall.
It is advisable to only cut those plants that can be thrashed and winnowed on that same day.
Harvesting should be done on hot sunny days.
Mature soyabean plants left standing in the field, if wetted by rain, dry up faster than those that have been piled in heaps.
Small loosely arranged dome-shaped piles of dry soyabeans also dry out rapidly if soaked by rain.
To prevent rain damage, soyabean also can be cut and stored in a roofed shed to be thrashed at a later date when labour becomes available.

Shattering losses.
Between 14 and 28 days after maturity, soyabeans may start to shatter scattering the seeds to the ground.
This two-to-four week period is the window for harvesting the soyabean crop. Shattering losses can be as high as 70 percent.
So farmers must beware and make preparations to harvest as quickly and as early as possible.
Improved varieties take longer to shatter compared to older varieties.

Harvesting methods.
Harvesting methods fall into two broad categories: machine and hand harvesting. The main components of the harvesting process are: cutting the dry plants as close to the soil surface as possible, thrashing the pods to release the beans and winnowing to remove the chaff.

Combine harvesting.
Large scale farmers need to use a combine harvester which cuts, thrashes and winnows all in one operation.
The combine harvester is fast and allows large areas to be harvested quickly.
This is important where labour is in short supply and where it is feared that late rains might damage the crop.
Information about hiring combines can be obtained from agricultural equipment companies, AGRITEX, ARDA and farmer’s unions.
Some contractors arrange for combine harvesting of crops they have sponsored. Charges vary but are usually on a per hectare basis.

Charges for combine harvesting.
Charges for combining include a cash payment plus diesel supply.
Some contractors provide diesel and charge one flat price.
Yet others may accept payment in kind, that is they take a portion of the harvested soyabean crop instead of a cash payment e.g. 4 – 6 x 50 kg bags per hectare. Farmers are encouraged to shop around and negotiate for the best deal.
Prices charged by ARDA for various farming operations are a useful benchmark for comparison.

Tips on combining soyabeans
When using a combine harvester, some important considerations must be borne in mind.
The importance of leaving the crop to dry thoroughly has been stressed.

Pod clearance, i.e. the distance from the ground to the first pod on the stem must be long enough otherwise the machine will cut and leave some beans on the stumps.
If the crop is poorly fertilised or has suffered an early drought, pod clearance may be too low for effective combining.

The second point is lodging i.e. plants falling over either due to them being too tall, blown by wind or affected by termites.
All such plants must be propped upright or heaped and fed into the machine by hand.
Otherwise the combine harvester will trample fallen plants into the ground.

Cleaning field before combining.
A third point has to do with weeds.
All green weeds must be removed by hand or ‘burnt’ up using herbicides like paraquat.
If green weeds are not removed, they will interfere with the efficient winnowing of the crop, block the vents and also will colour the beans reducing their quality. Generally combine harvested soyabeans will have a certain amount of chaff or extraneous material.
Flat field surfaces make for easier combining.
Stones and large solid objects slow down progress and may damage the harvester; they must be removed before combining starts.

Combining efficiency.
Farmers must be aware that a combine harvester is not 100 percent efficient.
Some studies show the machines taking in up to 70 percent of the crop.
Hand labour may be required to glean the fields to recover the other 30 percent of the soyabean crop.
In fields with green weeds, lodged plants and uneven surfaces the harvesting efficiency is lowered.

Side cutters.
New soyabean harvesting technologies include side cutters that are tractor or ox-drawn.
Cut plants are then placed in the hopper of a thrashing machine driven by a petrol or diesel-powered engine.
Alternatively, the plants are cut and spread on a tarpaulin and thrashed with sticks as for hand harvesting.
More research is required to develop user-friendly labour-saving soyabean harvesters for small to medium scale farmers.
Overall the country is poorly served with combine harvesters.
Many of the harvesters are in disrepair while a few others are kept by owners as luxury status symbols.

Hand harvesting.
As early as possible in the .morning, while plants are still wet with dew, they are cut close to the ground and spread out to dry on a suitable hard surface or tarpaulin (tende).
Around mid-day the plants are thrashed and turned over and thrashed with sticks to release the beans from the now dry pods.
Alternately, where labour is not readily available, a tractor or even a span of oxen can be driven over the heap of dry soyabean plants.
This will effectively thrash the pods.
This is followed by winnowing to remove the chaff.
Hand harvested soyabeans are much cleaner compared to combined crops.
Again only a quantity of crop that can be thrashed on a particular day must be cut especially when there are fears of rainfall.
Soyabean plants that are heaped will rot if wetted by rain.
On average 3 – 5 x 50 kg bags can be hand-harvested in one working day.
Farmers usually pay by the 50 kg bag, but must take cognisance of other costs in the crop production cycle.
Harvesting can be disproportionately expensive.

In the next article we shall look at storage, grading and marketing of soyabeans.



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