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Harvesting and Storage

Labour constraints

timing critical -- crop-stage, moisture content, but weather, marketing important

need to harvest over relatively short period

harvesting is second only to weeding in labour requirements for ox or tractor based systems

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Ox-equipment exists for: ploughing, harrowing, weeding, threshing.

But - very little animal based mechanisation used for harvesting.

Ox-drawn groundnut lifter but harvesting stillhas to be done by hand.

Fork, hoe or stick ploughs to loose root crops such as potatoes, cassava, etc. need to avoid damage

Most farmers in developing countries harvest crops manually using simple hand tools such as sickle

Equipment

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Improved cultural practices

cultural practices affect post-harvest quality of a crop - timely cultivation, moderate use of nitrogen fertiliser, avoidance of drought, and control of fungal infection all increase storage potential

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Factors that govern timing of harvest

Maturity

maturity in this context is the stage of development at which the produce is most desirable

botanical maturity may be different e.g. cucumbers are sold when biologically immature

often need to harvest before maturity: to avoid shattering of grain or other damage produce such as fruit may become bruised, soft, unpalatable if harvested too late because crop is not all at same stage quality may improve if matured in storage to gain price advantage

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Moisture content

newly harvested crops susceptible to insect & fungus attacks if wrong moisture content

reduce moisture content before storage (e.g. grains to 8 to 12%) sometimes by drying in field – depends on weather

deterioration may depend on time of day crop was harvested

cover to keep rain off

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Drying in rows which are periodically turned - windrows

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Harvesting of rice - India

Optimum moisture for rice: 20-24%; wheat: 15-20%

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Sundrying sorghum– slightly less grain yield- slightly delayed peak in optimum time

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Delayed harvest of root crops as a method of storage

• traditional storage of sweet potato – leave crop in ground & harvest when needed

• many late-harvested tubers past prime & damage from sweet potato weevil (Cyclas spp.) likely

• cassava can be left in ground for 8-24 months after planting

• deterioration of cassava begins 1 to 4 days after harvest if no special treatment

• once harvested, simple techniques such as reburial keeping under water, smearing with mud and stacking with daily watering help to preserve the tubers

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Appropriate time of harvest

• fruits harvested at the appropriate time give the highest quality - e.g. for dessert banana, date of harvest is based on size rather than maturity, because the fruit can be ripened as required by exposure to ethylene – market standards dictate the size at harvest.

• plantains are mainly grown on small-scale farms – date of harvest depends on market demand, and financial needs of farmer - farmers may harvest fully mature fruit for their own consumption and local markets, and harvest less mature fruit for sale at distant markets

• fruits should normally be harvested early in the day, when temperature is low

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Pre-storage processing of field crops

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Separating grain from coating and vegetative parts

threshing detachment of grain from straw and / or seed covering - often by beating or using animals to tread

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dehusking, dehulling • removal of seed covering (in India, legume

dehulling performed on domestic grinding stone (chakki)

• commercial, medium to large-scale dehulling mills produce decorticated splits, commonly known as dhal)

Locally designed fonio(Digitaria exilis) dehusker - Senegal

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• decorticating – removal of unwanted parts of harvested material such as rind, husk, bark and/or vegetative parts - generally (but not necessarily) from crops other than cereals or legumes, e.g. cotton;

Sisal decorticator – South Africa

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cleaning – removal of unwanted material e.g. by winnowing

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Pre- and post-harvest losses

One Indian study indicated that for rice the followinglosses occurred:

during harvesting : 1 to 5%transportation : 2 to 7%threshing : 2 to 6%storage : 2 to 6%drying : 1 to 6%milling ; 2 to 10%

In DCs, post-harvest losses of cereals generally are between 10-20%.

Fruit and vegetable losses are often higher = 20-100%.

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Crop Storage & Post-Harvest Processing

Introduction

aims of storage are: to make products available all year round improve quality of some crops e.g. tobacco

Storage is essential element in post-production marketing chain.

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Political, social and economic changes are influencing crop storage strategies : -

• in some countries, market liberalisation encouraging farmers to store greater proportion of harvested crops on farm – can take more advantage of seasonal price fluctuations but benefits can be achieved only if the storage losses can be reduced

Political, social and economic factors in crop storage

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declining agricultural labour force and decreasing contribution of agriculture to GDP means alternative rural livelihoods are essential to limit rural-urban migration --- post-harvest activities (processing and marketing) tend to be labour intensive as well as providing added value - but depends on effective crop storage

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rapid increase in urbanisation means there is a greater

number of people relying on rapid, reliable transport of

food products, and efficient storage, processing, and marketing systems to give them secure food supply

- urban people, even in DCs spend less time

preparing food and demand more processed food - this increases the need for safe storage of crops and processed food

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policies, institutions, and technologies to improve village

level storage and processing technologies would have large impact on rural economy and promote increased

agricultural production to provide raw materials for

processing

consumer pressure - exerting increased pressure for higher quality food as well as environmentally safer technologies for pest and disease control in stored crops

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emphasis of post-harvest research therefore now changing from focus on farmers’ need to preserve harvest to ensure food security, to emphasis on developing technologies that enable farmers to generate more income by adding value to their crops and to promote generation of off-farm employment for people involved in the processing, transportation and marketing of food products

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Breeding & selection for storage

Potential for selection for storage - • duration best time of harvest to avoid rain, • ability to store for long periods without deterioration, • ethylene production,• resistance to storage pests and diseases, etc

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Root crops

• sprouting and spoilage of sweet potatoes common with most forms of storage - tubers usually cannot be kept for > 1-2 months -- red varieties store better than white

Fruit

• some genotypes have greater ability to retain market quality – e.g. storage life

• storage life must be weighed against other characteristics – e.g. plantain clones bred for resistance to the fungal disease, Black Sigatoka, have a reduced ripening period, and hence shorter storage life

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Biotic factors

Moulds type of fungi

develop on the surface of & inside stored commodities that have not been dried properly or which have become wet during storage – emit mycotoxins which are hazardous to human & livestock health (especially Aflatoxins)

occurrence of moulds can be avoided by reducing the moisture content of the crop as soon as possible – some crops may be left in field to dry but this increases risk of attack by storage pests

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grow most rapidly between 10°C and 38°C

at 90°C all moulds (and yeasts) are destroyed - though subjecting crops to these temperatures would destroy quality

moulds on cereal, pulse, spice and some fruit crops can be minimised by sun-drying either on the ground or on platforms under which fires may be lit to increase rate of drying

once in store, commodity must be kept dry

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Aflatoxins

aflatoxins are highly dangerous toxic residues produced by certain fungi, such as Aspergillus flavus and A. parasiticus - especially affect oilseeds, edible nuts and cereals in DCs

cause aflatoxic hepatitis and enteroergotism

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• toxins particularly carcinogenic in humans

• also liver cancer and other diseases

• acts as an immuno-suppressant

• livestock also at risk particularly poultry - cattle not so susceptible but, if they are fed on contaminated feed, the toxin can pass into the milk

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trade restrictions on contaminated produce

need better monitoring methods to reduce health risks & boost exports - ICRISAT have developed cheap test based on aflatoxin antibodies

prevention and treatment needed – integrated approach

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• drought, particularly just before harvest, can cause cracking of the groundnut pod, which enables the fungus to get inside the pod and invade the seed

• vital that crops are dried to a 'safe' moisture level as quickly as possible

• correct storage after harvest important

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Yeasts

also types of fungus act on starches and sugars to produce alcohol and CO2

valuable for bread, beer and wine

can make other food ferment when it is not desirable

reduce by drying or adjusting pH

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Enzymes

proteins that function as chemical catalysts – break down plant tissue after fruit or vegetable is picked

destroyed by manipulating T

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Insects

insects are most serious pests of stored grains & pulses - cannot easily be excluded from stores - infestation results in both weight loss and deterioration in quality

heat, moisture and waste products produced by insects may also result in further deterioration and the growth of moulds

store hygiene essential to prevent reinfestation of newly stored grain

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• under traditional systems, insect infestation often less serious problem because although local varieties were low yielding, they were also more resistant to attack by insects

• introduction of high-yielding grain & pulse

varieties has sometimes resulted in increased storage losses as these varieties often more susceptible to insect damage - though usually compensated by extra yield

• use of pesticides in food stores on farm level often too costly for resource-poor farmers;

• some farmers aware of dangers of chemicals and only use synthetic chemicals to treat grain they intend to sell

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Bruchid beetles (Callosobruchus maculatus and C. subinnotatuts) - major pests of stored legumes as wellas attacking mature pods in the field before harvest (except subterranean pods such as bambara groundnut )

damage and weight loss is caused by larvae which develop within the grain, consuming the seed

surveys in Ghana revealed that average weight losseswere <5% / month in cowpea and bambara stored on-farm - even with this small percentage the damaged beans effect the market price of the whole

other major storage pest in Ghana is the Khapra beetle, Trogoderma granarium

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Traditional insect control and storage methods

• smoking,

• radiation

• e.g. in some countries, thermal disinfestation of legumes (seeds laid out in the midday sun for 3 hrs) found to be effective if followed by treatment with oil e.g. Shea butter

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• admixing of dusts or ashes

• jute bags – especially maize & g-nuts

• baskets

• home – store in roof space – on the stalk - houses need better - weather-proof roofs

• raised platforms

• clay pots

• granaries

• fires under granaries reduce mould growth

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Granary in western Kenya

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Physical barriers

• vegetables oils for crops such as beans and other crops such as cowpeas, and maize, to reduce bruchid beetle & weevils attacks - large volumes needed - treatment expensive

• inert dusts, particularly diatomaceous earths (fine dusts)

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• diatomaceous earths have extremely low toxicity to mammals

• contact with diatomaceous earth particles causes the waxy fat and lipids to be adsorbed from the cuticle of insects resulting in water loss, dehydration and death

• 0.1% and 0.05% w/w have proved effective in maize

• ashes provide a sterilised physical barrier against insects - needs large quantities (min. 20% by volume) & grain has to be sieved or washed to remove the ash/dust before use;

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• preserve newly picked tomatoes by thin layers of ash between layers of tomatoes

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Chemical repellents

• insecticides of botanical origin – may only reduce and not eliminate

• Examples:• Neem, • Pyrethrum• Siam weed (Chromolaena odorata) - Ghana• Palaga (Securidaca longipedunculata - not

widely used – trials on vertebrate toxicity continue

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• chilli (Capsicum annuum)

• banana juice (pre-fermentation) for beans and maize – soak for a few moments and dry – chemical repellent?

• mercury pellets used in India as an ovicide but does not inhibit growth of larvae and pupae within the grain; if used early enough, they are effective; mercury not harmful in itself, but is converted in the body to methyl mercury - highly toxic.

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Using knowledge of life cycle

• for weevils, sacks of beans twice turned end-over-end 2-3 times a day – tumbling dislodges the weevils from the beans as they take 18 to 24 hours to drill through

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Use of natural predators and diseases

• larger grain borer (LGB) - Prostephanus truncatus – originally imported in relief maize - particular problem for maize farmers in Africa causing 30% storage losses in some countries - biological control now successful by its natural enemy,a predatory beetle (Teretriosoma nigrescens)

• use of entomopathogenic fungi (e.g. Beauveria spp.) as mycopesticides

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Rodents

• impact of rodents severe

• existing knowledge and technology on rodent control inappropriate for the control of rats in rural villages

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• rodenticides not an option – • too expensive, • not readily available, • likely to be dangerous if used incorrectly

• most effective means of control is good store management - rodent proofing - may prove difficult if crops stored in house

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• Rats pose public health risks:

• Bubonic Plague

• associated with other diseases such as Leptospirosis

• rapidly spread other gastroenteric diseases such as Cholera and Salmonella

• in one survey ... 100 rats per house in Mozambique - large number of people bitten by rats whilst sleeping at night, leading to secondary infections

• rats are sometimes eaten if caught - poison not an option

• development of trap shy animals

• covering drinking water vessels limits water resources available

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Improved field storage - especially fruit

after harvesting, fruit should not be exposed to sun, rain, or wind - collection points for the harvested fruit should be accessible to vehicles for transportation - collection points should also be shaded

grading at this point can also improve overall fruit quality. Farmers should discard diseased, damaged, or over-ripe fruit.

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Control of post-harvest environment

• most important factors affecting product quality during storage are rates of respiration & transpiration

• respiration and transpiration should be reduced as much as possible - often by controlling, individually or in combination temperature, humidity, ventilation, atmospheric composition

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• traditional methods for increasing the storage humidity include spraying P&Bs intermittently with water, storing fruit on wet sacking, and storing fruit in boxes filled with moist coir or sawdust – though these methods can cause excessive wetting, which leads to fruit splitting and reduces market quality

• air circulation is an effective method used to reduce temperature in storage rooms but ventilation also increases water loss from fruit

• if ventilation is used to reduce T, water loss can be reduced by covering fruit with tarpaulins, packing fruit into bags, boxes, or cartons, wrapping fruit in polyethylene bags or heat shrink plastic films

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• proper ambient temperatures and moisture .... over-heating caused by fungus and insects if too high

• high ambient temperatures and moisture causes loss of seed viability also - only critical if seed to be planted

• controlled atmosphere / ventilation rate needed for crops which emit ethylene because ethylene accelerates maturation

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Pits or trench silos: yams, cassava 0.5 m deep, floors covered with leaves & straw inspection difficult T & rotting

Raised huts also can be used for storing root crops:

During long storage, yam tubers lose moisture and shrivel - covering tubers with yam vines, straw or other similar plant material helps reduce shrivelling

Storage of root crops

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Drying

for storage or immediate sale as dried products, especially fruit

solar driers for rice, beans, fish, cocoa, coffee, cassava, maize, bananas, coconuts – contact Renewable Energy Resources Information Centre (RERIC) in Thailand

solar dried fruit in Uganda - Fruits of the Nile - being marketed in UK

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see http://www.wot.utwente.nl/ssadc/chapter2.htm#ch2.4 for more details

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• cashews - more complicated - boil apples in salty water then in sugar then dried in solar drier

• IRRI developed a simple, low cost electricity powered mechanical dryer for small-scale rice farmers in Vietnam – designs free from IRRI

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Sealing

• hermetic storage in plastic buckets very effective – but expensive

• polythene sheets for lining of bags & baskets feasible and effective

• for cassava, plastic-bag storage of fungicide-treated roots increases storage time to about 2 weeks

• plantains sealed in polythene bags remain green for a longer period than fruits stored in perforated polythene bags, paper bags, or wet coir

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Control of ethylene

• reducing ethylene levels delays ripening; using chemical ethylene absorbents or oxidisers, to reduce ethylene (e.g. inside polythene bags)

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Fumigation

• fumigants commonly used against pests:• expensive,• can affect human health • those containing methyl-bromide have been

banned as they deplete ozone layer

• aluminium phosphide fumigation tablets – mainly for trader level storage – should have training or supervision - does not provide long-term protection

• cotton or plastic sheeting placed over stacks of fumigated bags (to act as a physical barrier to insects)

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Sterilisation - fruit

pasteurisation of fruit juices by raising to temperature of 90°C for a few seconds