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An overview of rice post-harvest technology: use of small metallic silos for minimizing losses - D.J. Mejía

Agricultural Industries Officer, Agricultural and Food Engineering Technologies Service, FAO, Rome, Italy

INTRODUCTION

Rice (Oryza sativa L.) is a staple food consumed by over half the world population. The total world production of unmilled rice (paddy) is around 592 million tonnes (Mt) (based on the average production for 2000 and 2001). Ninety percent of this total is grown in developing countries, mostly in Asia, while Latin America and Africa produce 3.8 and 2.8 percent, respectively (FAOSTAT, 2001).

It is estimated that by 2025, 10 billion people will depend on rice as a main food and demand will reach about 880 Mt. Many Asian countries and international institutions agree to the strengthening of national programmes for policy and financial support to research, seed production and extension of hybrid rice (FAO, 2001). In fact, there has been an expansion of area under high-yielding varieties (HYV), and in 1998 more than 90 percent of irrigated areas in Asia were under HYVs (Evenson, 1998). Methodology on the impact of the improvement of productivity on postharvest operations has been developed by FAO for several crops including rice (Phan, 1998). As HYVs are increasingly used, the post-harvest system must be improved, including infrastructure development and also the dissemination of technologies, allowing small and medium farmers to prevent food losses and consequently to achieve the food security which is a priority of FAO in its fight against hunger.

The rice post-harvest system requires improvement in the use of resources for research and development, particularly with regard to the level of post-harvest losses. These losses are attributed to a combination of factors during production and post-production operations (De Padua, 1999).

This paper presents an overview of the main postharvest operations traditionally used by rice farmers in developing countries and the importance of post-harvest technologies for minimizing rice losses. Inadequately performed drying and storage operations contribute to increased losses. The advantages of the household metallic silo are discussed and it is proposed as a feasible and suitable alternative - highly recommended by FAO - for small and medium rice farmers. While this study does not address drying operations in detail, it should be noted that they are complementary to storing.

Post-harvest system

The post-harvest system consists of a set of operations which cover the period from harvest through to consumption. An efficient post-harvest system aims to minimize losses and maintain the quality of the crop until it reaches the final consumer. When food losses are minimized, both food security and income increase, and this is of vital importance for small and medium farmers, particularly in developing countries. From a socio-economic point of view, the implementation of an efficient post-harvest system in any community must provide equitable benefit to all those involved in the system (Grolleaud, 2001).

Post-harvest losses

The traditional concept of post-harvest losses - for the main part quantitative losses - is currently changing. Many post-harvest specialists recognize that measurement of post-harvest losses is a very relative concept for various reasons; for example, losses could be determined as a function of theoretical yield, real yield, soil and fertility conditions, variety etc. Then there are the other losses which are not normally measured, such as agricultural inputs, time, manual labour, lost opportunities etc. In spite of the above, when post-harvest losses are assessed - whether in grains, cereals, fruits or vegetables - the most practical approach (and therefore the norm) continues to be quantitative measurement. To obtain reliable data of post-harvest losses, it is nevertheless important to establish a methodology which takes into account a range of factors (cultivar size, plot size etc.). Data should be supported by basic statistical analysis in order to understand how efficiently a post-harvest system works (Calverley, 1994). Likewise, observations and rapid appraisal in situ by an expert may help to identify how efficiently a post-harvest operation system works within a rural community and for a specific crop.

The post-harvest system for rice deserves special attention: rice is a major staple food in the world and is mostly produced in developing countries where the implementation of post-harvest technologies is urgent in order to prevent food rice losses. It has been estimated that rice post-harvest losses may be as high as 16 percent. A study carried out in China revealed that total post-harvest losses ranged from 8 to 26 percent, with storage and drying the most critical operations (Ren-Yong et al., 1990).

Main post-production operations used by rice farmers

Paddy pre-harvesting operations

The quantity and quality of final milled rice depend on the efficiency of farming management, field operations and post-harvest operations. Decisions are taken from planting through to consumption of the rice crop. Initial decisions about the variety to be planted determine intrinsically desirable characteristics and depend upon consumer preference as well as the technical capacity of the farmers during production and post-production operations. These characteristics in turn become factors which influence efficiency, grain loss magnitude, choice of harvesting and threshing technology, rate and quality of the drying and dehusking process, and eventually total recovery of the milled rice. Then there are the wrong practices at the planting stage which can lead to losses: planting of red rice admixture, attacks by rodents and birds, poor weeding and a harvest maturity date which can be too early or too late.

It is important to point out that the differences in varieties planted in certain localities also affect the final milled rice, as the high-value rice market usually prefers a pure and single variety. Nevertheless, for reasons of biodiversity and more sustainable agriculture, planting different varieties (although not necessarily in the same field) is an excellent strategy for improved food security. Sometimes, high management is required to monitor planting in order to prevent varieties becoming mixed; on the other hand, varieties are sometimes deliberately mixed to produce special characteristics, such as consistency of flavour, which cannot be found in a pure variety.

During pre-harvest operations, efficient technology and input management, as well as timeliness of activities, are important, and this applies also to postharvest operations for good yield and quality and in order to obtain good prices for the milled rice and byproducts. Correct timing at harvest is essential to avoid losses incurred by harvesting too soon or too late. Immature grains harvested too early result in a high percentage of brokens and low milling recovery, while if harvesting is delayed, the crop is exposed to insects, rodents and birds, in addition to the risks of lodging and shattering. The optimum harvest time should be chosen depending on the variety planted (Lantin, 1997).

Table 1 shows the losses incurred if the rice is harvested 1 week early and up to 4 weeks late on the basis of the maturity date of the crop.

In general, the correct time to harvest is 1 week before the maturity date.

Others indicators for optimum harvesting time for rice are as follows:

TABLE 1
Grain losses at different harvesting times based on crop maturity

Losses (%)

0.77

3.35

5.63

8.64

40.70

60.46

Harvesting time (weeks)

-1

0

+1

+2

+3

+4



Maturity date





Source: Almera, 1997.

Harvesting

Harvesting includes numerous operations, including: cutting the rice stalk; reaping the panicles; laying out the paddy-on-stalk or stacking it to dry; and bundling for transport. Correct harvesting and handling operations can considerably reduce post-production losses. Excessive handling creates problems in terms of both quality and quantity.

The sequence of manual harvesting, field drying, bundling and stacking in traditional systems can cause losses of between 2 and 7 percent (Toquero and Duff, 1974). At this stage, losses can occur when secondary tiller panicles are missed when the sickle cuts 60 cm above ground in lowland rice. Also, delayed harvest causes shattering losses during harvesting and transport.

Harvesting methods

There are a variety of different methods for rice harvesting, with traditional manual methods prevailing in developing countries:

Panicle reaping

This is accomplished by using a hand-held cutting tool (Yatab in the Philippines, Ani-ani in Indonesia, Kae in Thailand, Espigadora in Bolivia). The method is used in areas where traditional varieties are resistant to shattering. Resistance to shattering is particularly important during handling and when transporting the bundles of panicles from field to house. The labour time required for this method is 240 labour-hours/ha (done mostly by women and older children), which is four times that required with the hand-sickle method. It remains popular because of the social custom of chatting while working. In addition, it generates income among the landless rural population and is suitable for hilly and terraced areas.

Long stalk cutting by sickle

This is a widely used manual method presenting different styles in the design. It requires between 80 and 180 labour-hours/ha. The stalk is cut about 10 to 15 cm above the ground or with a stalk length of about 60 to 70 cm for easy bundling and threshing. Reaping efficiency depends on various cultural practices, plant density and variety, degree of lodging, soil conditions and the skill of the harvester. Lodged paddy and saturated soils may considerably reduce the cutting rate.

Modern mechanical methods

These methods are generally used when labour is scarce; otherwise, harvesting is generally still done with a sickle in most developing countries. The use of mechanized harvesting methods in some areas depends upon the custom and suitability of the machine and other socio-economic factors. Some examples of these machines are:

There continue to be constraints for farmers in developing countries to the adoption of mechanical harvesting methods: low income, reluctance to move away from traditional methods, poor mechanical aptitude, the desire to save straw for off-farm uses, lack of access to the field, excessive moisture content, uneven ripening etc. Other limiting factors are the high cost of imported equipment and the fact that machinery management must be competitive with the relatively low cost of labour (IRRI, 1997).

Transport

In developing countries, transportation of paddy from the field to processing areas is performed mainly by humans and animals, and sometimes using mechanical power. In hilly areas where paddy fields are terraced (e.g. Bhutan, Nepal, some parts of the Philippines and Indonesia) the paddy is transported in panicles or bundles of long stalks using human or animal power. These traditional methods of transport, which are related to the harvesting and field drying activities, very often result in high grain losses. Small and family-sized volumes of paddy are generally transported in bags from the house storage to the small rice mill on foot, in bullock carts, by bicycle, using small vehicles or with public transport - whatever means is available and affordable. Other methods of transport include donkey, buffalo and even boat.

In some places, the practice is to windrow the cut paddy in the field to dry for 3 to 7 days, depending upon the weather conditions. Losses are even greater, especially if harvesting is delayed with respect to the crop maturity date. In addition to the losses incurred in cutting, wind-rowing, sun-drying, collecting and bundling of the cut crop, there are those when the bundled paddy-in-straw is loaded onto the person’s back to be carried to the house.

Grain then falls en route, especially with the transportation of shattering varieties, and also when the carrier (usually a woman) stops to rest. Nevertheless, some farmers prefer this method for both cultural and practical reasons, as the straw can be used as animal feed.

The large losses incurred are the principal drawback to manual transport. Threshing of the paddy in the field and transportation in bags (40-75 kg) can minimize grain losses, however. Sun-drying of the paddy can also be done in the yard of the house rather than on stalks in the field. The normal practice in Asia is to bring the paddy from the field to the roadside manually or using animal power; it is then transported to the drying area or rice mill by motor vehicle (e.g. tricycle, power tiller with trailer, tractor with trailer, truck or lorry). The loading and unloading of the bags require additional labour costs, and these are normally assumed by the buyer.

In developing countries and advanced developing countries, the paddy is harvested by combine and is handled and transported in bulk. The paddy is unloaded from the combine by an auger conveyor and loaded into a waiting lorry or tractor-trailer located on the field road (part of the infrastructure for mechanized rice production). The paddy is then unloaded from the lorry or trailer onto a floor hopper in the rice mill area to be conveyed to a mechanical dryer. Finally, commercial rice is bagged at the rice mill and normally transported to wholesale and retail markets by means of vehicles. This mechanized procedure results in much lower losses (Lantin, 1997).

Threshing

During threshing the paddy kernel is detached from the panicle, an operation which can be carried out either by “rubbing”, “impact” or “stripping”. Rubbing may be done with trampling by humans, animals, trucks or tractor; however, the grain becomes damaged. Mechanical threshers adopt mainly the impact principle, but there is also a built-in stripping action.

With a paddy thresher, the unthreshed paddy may be either held or thrown in. In the “hold-on” type, the paddy is held still in the cylinder while spikes or wire loops perform impact threshing. In a “throw-in” machine, whole paddy stalks are fed into the machine and a major portion of the grain is threshed by the initial impact caused by bars or spikes on the cylinder.

In a conventional threshing cylinder, stripping may also be used for paddy threshing; impulsive stripping normally occurs with impact threshing. In a throw-in thresher, large amounts of straw pass through the machine and some designs use straw walkers to initially separate the loose grain from the bulk of the straw and chaff (Lantin, 1997).

IRRI developed the Votex Ricefan thresher. A portable machine, as well as being suitable for both paddy panicles and paddy stalks, it may be adapted for wheat, corn, soybean and beans. The Votex Ricefan thresher has been widely accepted among Bolivian paddy farmers (Terán, 1996) and may be either manually or power-operated.

Manual threshing is pedal-operated and involves: treading; beating the panicles on a tub, threshing board or rack; or beating the panicles with a stick or flail device. The thresher consists of a rotating drum with wire loops which strip the grain from the panicle when the paddy is fed by hand. This equipment is portable, can be used in hilly areas and is easily operated by women.

In power threshing, the harvested crop is trampled by tractor or truck tyres in developing countries. The grain is separated from the straw by hand and then cleaned by winnowing.

Losses may occur during threshing for various reasons:

Drying

Paddy as a living biological material absorbs and gives off moisture depending on: paddy moisture content, relative humidity of the air and temperature of the surrounding atmosphere. The respiration of the paddy is manifested in various ways: decrease in dry matter weight; utilization of oxygen; evolution of carbon dioxide; and the release of energy in the form of heat. However, respiration is negligible when the moisture content is between 12 and 14 percent.

By and large, paddy is harvested with moisture content of 24 to 26 percent (higher in the rainy season and lower in the dry season). It has a high respiration rate and is susceptible to attacks by micro-organisms, insects and other pests. The heat released during the respiration process is retained in the grain and in the bulk due to the insulating effect of the rice husk, resulting in losses in terms of both quantity and quality. Therefore, harvested grain with high moisture content must be dried within 24 hours: to 14 percent for safe storage and milling, or at most 18 percent for temporary storage of 2 weeks when it is not possible to dry any faster. Delayed drying may result in non-enzymatic browning (stack-burning), microbial growth and mycotoxin production in parboiled rice (NRI, 1991).

Square areas (10 x 10 m) of concrete have been successfully used for sun-drying in rural communities of rice farmers in Bolivia (Terán, 1996). Small rural farmers in these regions also use tarpaulins for paddy sun-drying. The main constraint of sun-drying is the dependence on good weather conditions, which can become a serious problem, particularly in tropical rainy countries.

Losses due to bad drying practices range from 1 to 5 percent and it is mainly the quality which is affected. Good drying is crucial for minimizing post-harvest losses, since it directly affects safe storage, transportation, distribution and processing quality.

A temperature of 43°C is recommended for drying paddy for seeds and this can be achieved with shade drying. Higher temperatures can lead to physicochemical disorders in the grain (Zheng et al., 2000). The cheapest drying method is sun- or solar drying, practised by farmers, cooperatives, commercial millers and government grain agencies in most developing countries. Between 70 and 90 percent of the field harvest retained in the farm is sun-dried, with the work generally performed by women and children. Drying usually takes place on paved areas next to the warehouse and rice mills; the paved areas slope slightly so that water can drain away during the rainy season.

Early harvesting when moisture content is high helps minimize shattering losses in the field. In crops of high-yielding varieties it is necessary to dry large quantities of wet grain in the shortest time so as to minimize rice spoilage. An artificial or mechanical dryer speeds up the drying process, reduces handling losses, maintains grain quality and gives better control during drying.

The temperature for drying paddy should not be higher than 54.4°C for food grain using the dry batch system. Low temperatures help preserve the rice aroma principle 2-acetyl-1-pyrroline (Itani and Fushimi, 1996).

The choice of a drier system depends on several factors: drying capacity requirement, ease of installation and operation, portability, full heat source and the initial cost of purchase. A wide range of drying equipment and methods are available for rough rice, and computer models have been developed to assist agricultural research workers or farmers in their selection of dryers for a given crop and situation (Dissanayake, 1991).

The adoption of an artificial drying system by rice farmers has numerous constraints:

The main causes of losses during drying are as follows:

Paddy cleaning

This is an important operation and highly recommended not only on a large and medium commercial scale, but also on a small scale. It consists of the separation of undesirable material, such as weed seeds, straw, chaff, panicle stems, empty grains, inmate and damaged grains, sand, rocks, stone, dust, plastic and even metal and glass particles. The degree of cleanness of the paddy reflects to some extent the care applied during harvesting, threshing and handling.

In developing countries, farmers clean the paddy straight after manual threshing. First, they use hand-raking and sifting to remove straw, chaff and other large and dense materials, then winnowing, i.e. making the grain fall down to be collected on a surface such as tarpaulin or a nylon sheet. The method depends on air natural conditions and is very slow.

A hand- or pedal-operated blower may be used with a cleaning capacity of 250 kg/hour. Alternatively, an engine-powered fan is used and can simultaneously perform both operations: grading and cleaning. The latter is expensive but has the advantages of being faster and requiring less labour (particularly women’s labour).

A versatile model from IRRI, known as “GC-7” and with a capacity of 1 t/hour for paddy and 3 t/hour for maize, was widely accepted by Bolivian farmers (CIAT, 1996). The main advantage of this model is that it can be manufactured in developing countries in local metal workshops.

Cleaned paddy demands a higher price than non-cleaned paddy - an incentive for cleaning the paddy. In contrast, lack of cleaning often results in a higher concentration of contaminants in the milled rice. Another consideration is that stones and other hard particles shorten the life of the milling equipment. Finally, milling recovery is low when paddy is not cleaned (Lantin, 1997).

Storage

Paddy may be produced once a year or throughout the year. Productivity has increased due mainly to the use of HYVs in irrigated areas. Consequently, it is important to improve and expand the post-harvest infrastructure for better handling, processing and storage of the paddy. Storage is a critical operation and losses can easily occur if preventive measures are not taken.

In Asia, between 70 and 90 percent of farm-produced paddy remains in the farms and the rest is deposited in or sold to agricultural cooperatives or sold to the private sector. Appropriate storage is therefore required, both for rice for consumption (milled or paddy) and for rice for seed purposes. The storage structure must protect the paddy from: extreme heat or cold; moisture, which causes microbial and fungal growth; and insect pests and rodents which consume or damage the rice. In Bolivia, small metallic silos with a capacity of 115 kg have been successfully used by small rice farmers (CIAT, 1996).

At farm household level, storage is essential for food security or as a commodity bank for conversion into cash when required. Unfortunately, small-scale or marginal farmers often lack the resources to store large amounts of grain and do not have a large storage structure; they therefore are obliged to sell their paddy to traders or buyers immediately after harvest. They carry out no further processing (drying, cleaning and grading) because of the immediate need for cash, and there is a lack of incentive to dry, as there is no significant difference in price between wet and dried paddy. The paddy is only dried for safe storage, and then only the amount necessary for consumption or a little more for cash conversion or to sell at a better price.

The traditional storage structure used by farmers in Asia is a container made of woven bamboo, palm leaves or wood. Problems occurring include: spoilage due to high grain moisture, rain, storms or flooding; dirt contamination; losses due to insects, rodents and even theft; collapse of the structure (Lantin, 1997).

The main causes of losses during storage are:

The paddy retained for storage is sun-dried several times and cleaned before loading into the storage container. The farmer determines the dryness required for storage on the basis of experience. Dryness is measured by pressing a bunch of grains hard into the hand or biting several grains: a fully dried grain is hard. Paddy is usually stored with a moisture content of 14 percent or less. Paddy is normally stored in a 1-tonne-capacity container for 6 to 12 months. Losses in farm storage have been estimated at about 6.2 percent (Ren-Yong et al., 1990).

Milling

Paddy or the rice grain consist of the hull or husk (18-28%) and the caryopsis or brown rice (72-82%). Brown rice consists of: an outer layer (pericarp, tegmen and aleurone layers) called bran (6-7%); the germen or embryo (2-3%); and the edible portion (endosperm 89-94%) (Chen et al., 1998). The rice milling operation is the separation of the husk (dehusking) and the bran (polishing) to produce the edible portion (endosperm) for consumption. Although a theoretical mill recovery would be between 71 and 73 percent, in practical terms it is possible to obtain between 68 and 70 percent from a good variety of paddy. Milling losses can be reduced by adopting small-scale modern rubber roll sheller and introducing parboiling of paddy before milling. Table 2 shows the advantages and disadvantages of parboiled rice.

TABLE 2
Some advantages and disadvantages of parboiled rice

Advantages

Disadvantages

Milling or dehusking is easier and costs less

Bran removal is more difficult and costs more

Milled rice has fewer brokens and is nutritious

Cannot be used in starch-making or brewing

Increased head and total rice out-turn

Doubles the total processing cost

Rice is more resistant to storage insect pests

Rice easily becomes rancid

Bran contains more oil

Requires large capital investment

Less starch lost in cooking andkeeps longer


Source: Lantin, 1997 (adapted).

The extent of losses in the edible portion of the grain depends on a variety of factors, including: variety of paddy; condition of paddy during milling; degree of milling required; kind of rice mill used; the operator’s skills; and insect infestations. The milling operation produces: husk, milled rice, germ, bran and brokens, coming out as mixed products, depending on the rice mill used. The ideal moisture content for milling is 14 percent, as wet soft grain results in a powdery product, while very dry brittle grains result in broken and powdery material.

Rice mills vary from a manually operated hammer beam pounder or mortar and pestle to the sophisticated machines used in big commercial or government installations. In rural areas without energy, the beam hammer pounder or the mortar and pestle are used by farmers - usually the female members of the family. When an engine-powered single-pass rice mill is brought to the community, the manual rice mill inevitably disappears. Women bring paddy for milling to reduce the workload and the rice mill is also a place in which to socialize. As the volume of grain being milled increases and people become knowledgeable and more demanding concerning the quality of the milled rice recovered from paddy, rice millers upgrade their machines and bigger and efficient machines are required to satisfy demand.

Causes of losses during milling include:

Post-harvest losses

As mentioned previously, “loss” is a concept which is difficult to define. Quantitative losses, however, eventually provide a broad picture of where the losses occur and their relative scale, and how a specific crop is handled during post-harvest operations. Losses are estimated on the basis of the post-harvest losses in each stage and assuming that each loss found is a percentage of the amount remaining from the previous stage. Otherwise, if losses are determined on the basis of the original weight of the crop, the figure may be overestimated.

Table 3 shows the results of a study carried out by FAO in 1994 on total post-harvest losses in six rice country projects in Asia.

TABLE 3
Comparison of total recorded project losses

Operation

Sri Lanka

Thailand

Myanmar

Indonesia

Bangladesh

Nepal

Cutting

0.86

10.1

2.1

0.8

2.3

1.9

Field drying (including bundling)

0.5

1.2

0.4


0.7

1.9

Transport


1.2

0.4

-

0.5

0.5

Stacking, pre-threshing

2.8

1.4





Threshing (including cleaning)

0.5

0.9

0.4

-

1.4

2.2

Drying

-

-

-

2.9

2.3

1.6

Parboiling





1.9

-

Storage

7.5

-

-

3.2

0.9

6.3

Milling

-

-

-

4.4

3.8

4.4

Average total losses

12

14.6


12.2

13.2

16

Source: Calverley, 1994.

It may be inferred that total post-harvest losses average around 14 percent, while the average losses in storage alone are around 4.5 percent. In fact, poor storage practices are one of the main causes of losses in the various stages of the post-harvest system.

An economic rationale is applied on the basis of the total rice production in Asia in 2001, according to which around US$79 billion are lost (Table 4).

TABLE 4
Economic rationale for total rice post-harvest losses in developing countries, 2001

Description

Estimate

Mt

World rice production

100%

585

Production in developing countries

90%

526

World production by small and medium scale farmers (assuming 80% in developing countries)

80%

421

Expected rice production in developing countries by small and medium farmers.

100%

489

Real global rice production among small and medium farmers.

86%

421

Total post-harvest losses

14%

69

Total economic post-harvest losses

Assuming a cost of 100 US$/t

US$69 billion

STORAGE POST-HARVEST LOSSES

As storage is one of the most critical post-harvest operations, it deserves special attention in order to estimate the economic magnitude of its negative impact. Table 5 presents a rationale based on the data collected in Table 3 (paddy production, 2001), with 4.5 percent of losses resulting from bad storage practices and a loss of around US$23 billion.

TABLE 5
Economic rationale for storage rice losses in developing countries, 2001

Description

Estimate

Mt

World rice production

100%

585

World rice production in developing countries

90%

526

World production by small and medium farmers (assuming 80% in developing countries)

80%

421

Expected world rice production without store losses

100%

441

Expected world rice production.

95.5%

421

Losses only during storage

4.5%

20

Economic losses as a result of poor storage

Assuming a cost of 100 US$/t

US$20 billion

A technology for rice loss prevention in-store: household metallic silo

A valuable structure highly recommended by FAO for small and medium rice farmers is the small metallic silo (Plate 1). The small metallic silo can play an important part in the fight for food security and against hunger in developing countries. Its effectiveness for safe storage has been proven since the 1980s. The technology was introduced as part of the Swiss cooperation for development in Central America, since when more than 230 000 small metallic silos with a capacity of between 0.5 and 2 tonnes have been introduced to prevent food loss. It has been estimated that more than 2 million people currently benefit from this technology in Central America. An FAO project in Bolivia on the prevention of food losses, GCP/Bol/032/Net, has successfully introduced more than 20 000 small metallic silos in the last 5 years.

PLATE 1
A silo

Source: FAO, 2002.

Advantages and characteristics

The silo is a simple storage technology, it is relatively easy to implement and helps preserve good quality grains and cereals. It helps strengthen food security in communities as it provides daily livelihood and economic support for small- and medium-scale farmers.

The most important advantages of the metallic silo are as follows:

Requirements for successful adoption of the silo

Cost of the silo

The cost of the technology varies depending upon the size of the silo and the country where it is introduced (Table 6). For example, in the recent workshop prepared by the Agro-Industry and Post-Harvest Management Service (AGSI-FAO) in Cambodia, the cost of the silo was seen to be lower than in Bolivia or Nicaragua.

TABLE 6
Cost of the silo

Boliviaa

Size (kg)

120

250

500

1 800

Cost (US$)

20

35

60

92

Nicaraguab

Size(kg)

180

360

540

810

1 350

1 800

Cost(US$)

22

28

44

51

64

100

Cambodiac

Size(kg)

120

250

500

1 800

Cost(US$)

10

20

28

45

a Mejía, 1998.
b C. Gómez, personal communication.
c Kunthy, 2001.

Implementation of the silo creates a positive critical mass impact in rural communities, as it increases economic activity and generates employment (e.g. for the village tinsmith who must satisfy the hardware requirements).

FAO STRATEGIES FOR TRANSFERRING THE SILO TECHNOLOGY

CONCLUSIONS AND RECOMMENDATIONS

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