POSTHARVEST TREATMENT OF SORGHUM (Sorghum bicolor) IN

BOTSWANA

INTRODUCTION

Sorghum (Sorghum bicolor) is undoubtedly the staple cereal of Botswana and is grown widely in the country. Eisener et al (1982) reported statistics of surveys conducted in the Southern and Southeastern districts of Botswana, in which 96% of the respondents indicate that they eat sorghum. Of these, 89% ate sorghum daily. In another study reported by IICT (1997), conducted in Northeastern Botswana, 52% of the respondents ate sorghum-based foods every day. Sorghum is usually paired with millet in terms of importance, but the latter is currently grown only in some areas of the northern part of the country and is still at the very initial stages of development for commercial exploitation (Kebakile et al, 1996). Several varieties of sorghum and millet, both indigenous and exotic, are grown in the country. All these varieties have proved to be of good food value, and may be use for different industrial applications. The development of these varieties, and their subsequent use, has been steered by a number of institutions in the country and abroad, notably, the Ministry of Agriculture, SADC/ICRISAT, THE Botswana Technology Centre (and its international collaborators-CIRAD, NRI AND IICT), and others.

An identified constraint that continues to hinder the national objective of food security is postproduction losses. These losses are believed to be high in magnitude although there are no loss assessment studies carried out in the country. These losses are caused by a number of agents, mainly insects and postproduction practices.

This paper seeks to examine post harvest treatments of sorghum and highlight the challenges and opportunities facing the crop post harvest

BACKGROUND

Historically, agriculture was the main form of economic activity for the majority of Batswana. At independence in 1966 the contribution of agriculture to the gross domestic product (GDP) was about 40%(NAMPAD, 1999). The sector is now experiencing a decline mainly due to the large increase in the role of mining and quarrying sector from zero to 33.5% in 1997/1998. Agriculture now provides 3.1% of the current GDP, while industry, including mining, provides 42.4% and services 54.5%. Agriculture still plays an important role in the economy of Botswana because 70% of the rural households are engaged in it.

Crop production

Table 1 and figure 1 show crop production for the main cereal crops mainly sorghum, maize, millet, pulses and others from 1991/1992-crop season to 1999/2000

The most important food grown in Botswana is sorghum, and because of its greater resistance to drought and high temperatures it takes up approximately 60% of the arable land planted. Maize is the second most important crop but it is mainly grown in the higher rainfall areas of the southeast and northeast. Various types of millet are also grown, mostly in the northeast where consumer demand and preference is stronger. The other important crops are cowpeas and beans. The average yield for cereals and pulses is 200kg/ha and 150 kg/ha in traditional subsistence farms (NDP, 8)

Table 1 Crop Production (‘000 tonnes)

Year	Sorghum	Maize	Millet	Beans	Other	Total
91/92	16.000	3.000	5.000	3.000	1.100	28.100
92/93	16.527	4.254	1.546	0.718	3.574	26.619
93/94	37.100	10.800	3.591	2.394	0.798	54.683
94/95	11.469	2.310	0.990	0.660	0.220	15.649
95/96	77.800	19.509	8.100	5.400	1.875	107.673
96/97	16.807	11.624	0.000	0.000	5.858	34.289
97/98	9.083	1.121	1.204	0.803	9.488	21.699
98/99	13.736	4.962	0.000	0.000	15.289	33.987
99/00	11.322	9.347	0.000	0.000	8.948	29.617

Figure 1

Source: Early Warning Unit

POST HARVEST TREATMENT OF SORGHUM

Harvesting

Depending on weather and scale of production harvesting usually begins in mid may and continues through to September. Except for the commercial farmers in the Northern part of the country (Pandamatenga) who use machinery most subsistence farmers use hand harvesting.The heads of the sorghum are cut from the stalks either by hand or using a knife, placed into sacks and taken to the threshing platform where they are placed on racks or spread on the platform for drying

Proper drying is considered to be one of the greatest factors in determining whether grains will be effectively stored without damage (SADC, 1984). When the grains are piled on racks or heaps to dry there is lack of air movement, leading to sprouting, discoloration and microbial damage. In addition losses may occur due to rats, birds, insects etc.

Threshing

Threshing is done by hand .The plant heads are either onto bags or left on the threshing platform and then beaten strenuously with long sticks until the grain separated. This method is very inefficient and slow and complete recovery of grain is not easyThe grain and chaff are then gathered together and hand winnowed using a small shallow basket. Losses occur during threshing by spillage; incomplete removal of grain from stalks; by damage to grain during threshing, by poor separation of grain cleaning or winnowing after threshing. Little information has been documented on the magnitude of losses during threshing in tropical Africa (Hamilton, 1980)

Storage

The two common practices used are the traditional storage and modern storage. The two main types of storage in Botswana are the mud crib and the grass basket. Although still used in many parts of the country, both forms appear to be slowly disappearing and becoming obsolete as the more modern and convenient forms are being introduced. With regard to modern storage, there are basically two form which have been adopted in recent years; silos and the most widely used jute bags and Hessian bags. The large commercial grain silos and warehouses are commonly used by Botswana Agricultural Marketing Board and milling plants. The jute bag is more popular among farmers simply for the following reasons:

- cheap and inexpensive to maintain,

- ease of moving between the farm and village

- only form readily accepted in the marketing system

During storage, grain is subjected to qualitative and quantitative losses due to several agents including insects, fungi, rodents and mites. Insects and rodents eat the grain and also contaminate the grain with their eggs, exoskeleton (insects) droppings, hairs and urine in the case of rodents. The magnitude of losses due to these agents is believed to be high although there are has been no loss assessment studies carried to date in Botswana. There is urgent need to carryout loss assessment studies to ascertain the magnitude of these losses so that appropriate action can be taken.

Grain protection and preservation.

The problems and damage pest infestation can cause to stored grains are well known and appreciated by farmers throughout Botswana, and various traditional and improved methods of protection are being used to reduce losses. Traditional methods of treating grains are widespread, and the most commonly used ingredients are cow dung ash and wood ash. Both are usually at the time the grain goes into storage. Improved methods being used in Botswana for the protection of stored grains against insect infestation, are through the wider use and application of contact insecticides and fumigants.The most common contact insecticides are Malathion 1%, ,Methacrifos 2% and Perimiphos-methyl 2% dusts. The fumigant most commonly used in Botswana is Phostoxin(Aluminium phosphide)

Processing

Sorghum grain processing involves turning shelled grain directly into consumable product (food). The process goes through primary processing which involves cleaning, dehulling(decorticating), pounding and milling to mention but a few. Then comes secondary processing, which involves turning material into food, i.e cooking, blending, fermentation and roasting.

Primary processing

In Botswana sorghum grain require the removal of the outer layer before any further processing could be done. The outer layers of certain sorghum varieties seed contain tannins , which are slightly toxic and have a bitter taste. For this reason it is normally dehulled and then pounded into flour. Traditionally the processing of sorghum and millet has been carried out by grinding the whole grain between stones of by pounding grain using a pestle and mortar. The latter is the commonest. The grain is then winnowed using leselo to remove the bran. Pounding and winnowing are repeated several times before good quality flour is obtained. The objective of hand pounding is thus twofold, the first is to remove the bran and the second is to produce the flour, but this is time consuming and backbreaking.

The improved methods of processing sorghum and millet involve two stages, which use a dehuller and a hammer mill, thanks to the Rural Industries Innovation Centre(RIIC) which designed the sorghum dehuller. The dehuller is used to remove the bran from the sorghum before it is milled. A dehuller has a abrasive discs or stones set on a horizontal shaft rotating at a high speed inside a casing. The bran is rubbed off by the grinding action of the spinning stones and the friction of the other grains.

Secondary processing

After primary processing, cereal products, flour or whole grain are further processed in the home and by a small cottage industries into final products. Common final products include foods with porridge, fermented drinks, and weaning foods. Sorghum/millet porridge is the most common directly consumable food from secondary processing of sorghum/millet grain inBotswana. The traditional sorghum and maize beers, and chibuku are good examples of fermented drinks from sorghum and maize. The other application of sorghum found in Botswana was for the weaning food ‘Tsa Bana’. There is still a great potential for sorghum to be processed into snack foods, breakfast cereals, whole grain foods and baked products.

Packaging

Packaging of agricultural produce is one of the simplest cheapest value adding operations that can be managed by most small food processors located any where in the country. A brilliant attempt was made by Botswana Agricultural Marketing Board (BAMB) in the early 80s to promote form of processing, but this seems to have died a natural death. An attempt form of processing was made with dehulled sorghum rain (‘sorghum rice’) to pack in 200g-500g packs. Some millers have tried to pack this ‘rice’ in the past but it failed to win a share of the market. Failure of this product to penetrate the market was largely blamed on the poor presentation of the product to the consumer( Kebakile et al,

1997)

Marketing

In the past years, there was no organized market for crops in Botswana. The marketing of grain crops inBotswana was largely undertaken through the few co-poratives exixting at the time and private traders who were slightly sensitive to economic interests of producers and consumers. A break through in the marketing system of grain crops came with the establishment of Botswana Agricultural Marketing Board (BAMB) in 1974 and its functions were:-

i. to secure a stable market for grain crops

ii. to ensure efficient and fair distribution throughout the country at fair prices to the consumer and producer.

iii. To provide infrastructure for the supply of agricultural inputs

At present BAMB operates depots in 15 major towns and villages for the purchase and selling of grain. In addition the board has nine agents, mainly co-operatives that buy grain on its behalf. Besides BAMB, there are privately owned commercial mills that buy grain.

Total Post Harvest System

Harvesting

Pre drying in field

Threshing

Winnowing

Drying

Storage

Sacks,bags,bulk

Primary Processing

Cleaning,grading,hulling,pounding,milling

Secondary Processing

Cooking, blending, fermentation

Packaging & Marketing

Post harvest constraints

Post harvest loses
Lack of grain storage facilities
Lack of credit facilities
Poor telecommunication networks
Lack of access to the markets
Lack of research capability in post harvest issues
Inadequate trained postharvest extension agents

Opportunities

REFERENCES

Report on the proceedings of the National Post Harvest conference, 6^th-8^th October, 1998. Ministry of Agriculture (MoA). Gaborone, Botswana.

Botswana National Development Plan 8, 1997/98-2002/03.

Boiling, M.B., Eisener, N. (1982). Bogobe: Sorghum porridge of Botswana. In: Proceedings of the International Symposium on Sorghum Grain Quality, ed Mertin,JV. ICRISAT, Patancheru, India, pp 32-35.

Hamilton, A.G, (1980). Review of Post Harvest Technologies in Botswana. Projects Division, Canadian University Services Overseas (CUSO), Ontario, Canada.

Kebakile,M.M., Mpotokwane,S., Botsalo, S.B (1996) Revew of Millets in Botswana; Production, Processing, Marketing and Utilization. A Study carried under the ‘ Collaborative Project to Investigate Consumer Prefernces for Selected Sorghum and Millet Products in the SADC Region of Africa’. Botswana Technology CENTRE- food Technology Research Service.

Early-Warning Report, June 2000.

Kebakile, M.M., Mpotokwane, S., Botsalo, B.S.(1997). Scientific Project REPORT: collaborative Project to Investigate Consumer Preferences for SELECTED sorghum and Millet Products in the SADC region of Africa

National Master Plan for Agricultural Development,(NAMPAD), 1999 Report. Ministry of Agriculture. Botswana.

Proceedings of A Workshop on Post Harvest Loss Prevention in the SADCC region. Harare, Zimbabwe.