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Because there is a wide choice of equipment available for both harvesting and threshing, it is not easy to select the machinery most appropriate to a particular situation. It is very important, therefore, to identify the constraints specific to each situation before selecting equipment.


Technical Constraints

(i) Cropping and Farming Systems

Previous analyses of the cropping and farming systems are required to determine the actual needs regarding mechanization: location of the land under cultivation, intensification level, prices of products, etc.

The mechanization of the harvesting operation for crops - mainly food crops - with yields ranging between 0.5 and 2 tonnes per ha rarely justifies itself economically.

On the other hand, mechanizing the harvesting operation will be more easily justified on an intensified irrigated area of several hectares with paddy rice as main crop, where small farmers can group together, and the sale price for paddy is sufficiently attractive.

(ii) Cropping Conditions

The constraints affecting harvesting and threshing operations which influence the quality of the product are: the moisture content of the grain at harvest time, the maturity of the crop, the type of plant involved and the way it stands in the field.

The moisture content of the grain must be between 18 and 23% at harvest time, or between 12 and 20% at the threshing stage. These guidelines determine the start of operations. Below such values, losses (in the case of rice) from shattering during harvest and breakage during threshing are excessively high and bad for the subsequent processing. Above such values, problems arise at storage level: risks of moulds developing and germination of the grain in stooks, drying cribs or granaries.

Crop maturity and type directly affect mechanization and vice versa. The introduction of mechanized technology has reduced the tendency to plant mixed varieties of grain: single variety crops ripen uniformly thus making it easier to harvest or thresh them mechanically. With crops which do not mature at one time, the choice of the date for performing the harvesting operation will determine the results: for paddy an earlier harvest will generally result in low yields and high percentage of unripe grain; on the other hand, delayed harvesting will lead to shattering losses, higher percentage of broken grain at the processing level, etc. In addition, the weed infestation level will affect the use of machines and also the cleanliness of the harvested and threshed materials.

The type of plant influences both the choice of machines and their performance:

To meet these objectives, it is necessary to observe a very strict work schedule, especially for wetland paddy. Accordingly, machines must be able to work under particularly difficult conditions: in the mud with special attachments (tracks, cage-wheels, etc.) before the complete drainage of rice fields, at low working speeds, on a produce difficult to cut because still partially green, and handling of a product often soiled with mud.


Social and Labour Constraints

Harvesting is a labour-intensive operation but is less arduous than threshing. Because most of the rural population consider threshing as a particularly tedious operation (especially in the case of millet), grain producers accept the relatively high cost of mechanical threshing.

The skills and experience of farmers, and the interests of traditional systems, must necessarily be taken into account when mechanizing certain operations. It will be easier to extend the use of harvesting machines where farmers are already employing other powered equipment such as tractors, motor pumps or processing units. The availability of workers skilled in the operation, maintenance and repair of engine-powered equipment favours the adoption of new machines.

Lastly, in developing countries harvesting and threshing operations are traditionally carried out by women. However, in most situations, as these operations become mechanized, they are taken over by men and the role of women is reduced to winnowing and the gleaning of grain scattered during harvesting and threshing. The mechanization of post-harvest operations frequently means the transfer of activities from women to men.


Economic Constraints

Economic constraints are a drawback to the purchase of farm machinery. The high costs involved, above individual farmers' resources, allow the acquisition of such equipment only if credit and the possibility of farmers grouping together exist. Alternatively, if private individuals are interested in equipping themselves, they can hire out their services to the rest of the community.

To justify and encourage the purchase of machines, technical versatility can be an incentive (e.g. a rice thresher which can also be used for threshing millet and maize), even if the equipment proves less efficient with certain crops than a specific single-purpose one. In such a case, the choice of the equipment should be made according to the crop which is mechanized first.

In practice, the costs of machines and services vary from one country to another. By way of example, the following 1992 tax-free prices for some machines in Senegal are given for comparison:

Thresher, Votex Ricefan 1,100,000 Fcfa
Thresher, SISMAR, Borga type 7,700,000 Fcfa
120hp rice combine harvester 24,000,000 Fcfa
Millet thresher, SISMAR (without tractor) 7,700,000 Fcfa
Multipurpose Bamba thresher, Bourgoin 2,200,000 Fcfa

Supplied services are generally paid a percentage of the crop: 5 to 10% for threshing and 15 to 20% for combine harvesting.

In Mali, the cost of using the Votex thresher is estimated to be between 3 and 5% of the grain produced (paddy at about 70 Fcfa per kg); assuming that the useful life is 10 years for the thresher (7 years for the engine), and that the working parts will need replacing after processing every (a) 80t for the thresher teeth, (b) 800t for the crimp screen and (c) 1000t for the thresher unit (toothed shaft and fan).

These figures must be considered as basic, because the profit margins of manufacturers and retailers of spare parts are not taken into account, and also because prices can be higher in other countries (as in Senegal).


Organization of the Distribution System

The introduction and extension of new machines is easier if distribution systems for machines and spare parts, and local industrial or artisan manufacturing facilities exist already.

Compared with animal-drawn implements, powered harvesting and threshing machines are difficult to manufacture. Research has been conducted into the design of simplified equipment which can be manufactured locally, e.g. the IRRI and Votex threshers.

Support from technological transfer projects has often been needed for the local production of some machines: the Votex Ricefan thresher in Mali and Senegal, for example. This thresher has been designed to cope with transport problems and allow local assembly or even partial manufacture.

Local construction will develop in several steps:

  1. The assembly of imported kits;
  2. Partial manufacture, except cylinder and gear case, by using cutting, punching, drilling and welding jigs; and
  3. Total manufacture, except some elements made of high-quality steel.

Theoretically, local manufacturing offers various advantages such as reduced profit margins to retailers and transport costs (100 kits in one container instead of 22 Votex threshers, etc.), but also some drawbacks (quality of construction and employed materials, adverse taxation and customs regulations, etc.).


Training Needs

In most developing countries, mechanization is far removed from traditional practices and its acceptance is a delicate matter for many farmers. Accordingly, training is a key element in the successful adoption of engine-powered machines by farmers.

Appropriate training of several types is required:

This training should be complemented by supplying information on, and demonstrating, new harvesting, threshing and cleaning equipment to farmers so as to increase their awareness of the range of machines available.

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