6. Seeding

6.1 Requirements of seeding

Seeders represent the highest technical demands of all the implements in the survey in the area of animal traction to date. They require precision in manufacturing and assembly, since many parts need to be milled and shaped. As a lack of parts however can hinder the distribution of implements, the technical aspects are dealt with in greater detail here. The experience gained can reveal information on the further developments of draft-animal technology.

In principle, seeding can be done by three methods:

- broadcasting,
- dibbling,
- drilling.

Additionally, there are three procedures for planting or transplanting (tubers, cuttings, seedlings). Broadcasting takes place on the soil surface and is generally done manually. The procedure is primarily applied for small seed that does not require a great seeding depth, as for example wheat and rice. The seed is subsequently worked into the soil by harrowing. After seeding no further work occurs with draft animals.

Drilling procedures necessitate the transition to seeding in rows. This means a higher draft power requirement, so that the use of hand-pushed seeders is only possible on well prepared soils. On the level of animal traction two procedures are applied: manual seeding in furrows, which are prepared by animal-drawn ards (figure E 23), or the use of drilling machines.

Animal-drawn planters, for example for sweet potatoes, potatoes, yams cassava or sugar cane, are not employed in cropping measures in the regions investigated. Star-type planting holers are only known in pilot projects.

A transition from broadcasting to hand seeders or animal-drawn seeders is occurring for the following reasons:

- increase of area performance,
- more exact seed depositing in regard to depth and spacing,
- ease of work by means of greater seeding density,
- maintaining rows more precisely to facilitate subsequent work operations.

A more appropriate adaptation to the various soil fertilities or the planned quantity relationship of adjacent crops in mixed cropping should be achieved by means of the exact maintenance of the seeding density. Further goals are the saving of seed, a more even distribution regarding emergence and maturing and a better distribution in the stand spacing. Saving seed is particularly economical if expensive seed (e.g. hybrid) is being used. An adaptation to the supply of moisture and the requirements of the respective crop can be accomplished with an exact regulation of the depth of depositing the seed. The exact maintenance of the seed depth facilitates an increase of yield for sensitive crops. Sowing in rows is a pre-condition for the use of animal-drawn seeders.

In contrast to simple manual methods the area performance increases fourfold and in comparison to manual implements such as the jab planter it is approximately doubled. According to the survey the area performance of animal-drawn seeders is about 6 h/ha (with maize). In an experiment with Brazilian implements 3.5 to 4.0 h/ha were recorded (Casa et al., 1987). For a manually operated dibbler an area performance of 3.5 h/ha was achieved (Wijewardene and Waidyanatha, 1984), which appears to be very high. Seeding in rows required for animal-drawn implements does not always offer an optimal space for the crops. If the seeds are deposited singly, as is occasionally the case for maize, the seed spacing is less important, for example for precision seeding.

Under certain circumstances draft-animal implements offer the possibility of practising non-tillage on unprepared soil, which can also be carried out with manually operated jab planters or dibblers.

6.2 Implements for seeding

6.2.1 Furrow breaker and row marker

Furrow breakers (figure E 50) are frequently used for keeping orderly rows or facilitating the work with animal-drawn seeders. They are then a particular advantage when organic residues or clods lead to clogging of the implements.

For marking the row spacing simple own designs are appropriate.

6.2.2 Seeders

With regards to seeders one distinguishes between the dibbling and row-seeding method.

6.2.2.1 Dibbling seeders

Pulled or pushed dibbling seeders follow the example developed by IITA (Wijewardene and Waidyanatha, 1984) having a hopper and equipped with a wheel. The tips, which are opened by a lever when the earth is touched, penetrate the soil and release the seed. The lid is subsequently automatically closed by gravity. Because of the fixed spacing of the tips the number of kernels in the row can only be modified by the spacing wheel, leading to pocket drilling. An exact number of plants can however not be assured per row. Dibbling seeders can be equipped with small front wheels for the purposes of transport and maintenance of working depth. The adjustment of depositing depth is done by a press roller.

The implement has the advantage that without possessing any substantial weight it can nevertheless penetrate unprepared soil or cut through a mulch cover. It also hardly becomes clogged in fields having a high proportion of vegetation residues. According to our experience however the implement has in practice proved to be a failure in the survey regions, both as a hand-operated implement and for animal traction. It has a tendency to prematurely trigger the opening mechanism, for example by pebbles or root residues or simply by centrifugal forces, which are too high even at speeds usual for draft horses. Furthermore, the tips become stuck with high humidity or in clayey soils. The seeding mechanism (planting jaws) is subject to breakdown; it closes poorly only if slightly damaged. It is difficult to exchange the seed-plate which regulates the spacing. (Casao et al., 1987; N 1989; v.d Decken, 1989)

In trials with various seeders in Brazil the Grazia rotary injection planter (figure E 52), which did not go into production, achieved the best results in terms of weight, maneuvering time, clogging susceptibility and area performance, and second lowest in draft power requirement. However, it is not suited for planting cotton. (Casao et al., 1987) In order to exploit the basic advantages (no clogging, possibility of seeding in mulch, low power requirement) a further development of this principle would be worthwhile. Its disadvantages could possibly be eliminated by the selection of a different principle for dosage and the punching mechanism (e.g. the spade principle; compare Shaw and Kromer, 1987).

6.2.2.2 Row seeders

For row seeders a distinction is made between drills and precision seeders. According to the survey usually single-row precision seeders are used for animal traction where rainfed cropping is practised. The seeders have been partially developed for the regional prevalent cashcrop, e.g. the Super Eco for sowing groundnuts in Senegal (figure E 53). Usually, the adaptation of designs to other crops took place later. A compromise had to be found between the precision of seeding of individual crops and the suitability for various crops, since the procurement of special implements is not worthwhile otherwise. Multi-row drills for small-kernel seed are not used in practice in the area surveyed. Various models of direct drilling machines do exist in Brazil for the purposes of experimentation.

These seeders are suited for the planting of larger seed such as maize, beans, groundnut and soybeans. With alteration some implements (e.g. most Brazilian seeders) can plant undelinted cottonseed. In Senegal the Tamba implement has been developed for this purpose; it is used for pocket drilling. Precision seeders are less suited for planting small-kernel seed, which can more easily be distributed by slide and cam wheels than by holediscs or spacing wheels. Nevertheless, precision seeders are often used for sowing of millet and sorghum.

To date there are no special seeders for ridged crops which allow the track, the frame height as well as the position of the press roller to be adjusted for width and height of the ridges. Furthermore, the seeders are notorious for their poor stability on the ridges. For this purpose Nolle (1984, in: Bordet et al., 1988) states that a drawbeam is required. He suggests a prototype having a stabilizing furrow opener, adapted to the ridge shape and the design of ridger. Another problem is that the farmer cannot walk on the ridges and that in any case two draft animals are required. The combination of mechanical ridging and seeding is not satisfactorily possible due to these special requirements.

The poor adaptation of seeders to sowing on ridges is also due to the fact that in some countries, e.g. Senegal, ridging is not the object of a development programme and under certain circumstances seeding is not a bottleneck in regions having ridged crops due to the longer vegetation period. (Havard, 1988a; Bordet et al., 1988)

The precision seeder requires the farmer to adjust the implement to the respective seed by exchanging the hole disk. Generally, precision seeders demand clean and calibrated seed. If no hole disks are available for the desired crop the farmer can not utilize the implement, if he does not want to risk considerable damage to the seed or too high seeding density.

Marking discs are seldom used on seeders. This is possibly attributed to the fact that precise seeding in rows is first required when multi-row weed control becomes necessary.

6.2.2.3 Experience with design and maintenance

Drive and distribution mechanism

Most Brazilian seeders have a front wheel which operates the drive e.g. the Sans seeder The press roller propels the drive of the Brazilian Triton (figure E 55) or the Safim in southern Africa. The transfer mechanism can be simplified by means of the side wheels in the Super Eco (figure E 53). Under certain circumstances utilization is also possible on low ridged crops (Metzger, 1988; v.d. Decken, 1989). Implements with two wheels are more susceptible to clogging and can hardly be used on slopes. The Super Eco is only suited for light, well prepared soils. It tends to plug up where weeds, vegetation residues and moist soil exist. The drive wheels must turn freely and faultlessly in order to assure an even seeding density. If they are not equipped with a tread (e.g. Super Eco) they can slip on loose soil. Also, larger clods or failing to grease the drive wheels can lead to a blockage of the drive. On slopes the front wheel tends to deviate from the row.

A special gear must be placed between the drive wheel and the dispensor in order to be able to deposit the desired amount of seed. Generally, the gear cannot be adjusted, but rather the seeding density is adapted to the selected spacing wheel (metering mechanism). Moreover, the transfer path should be as short as possible to prevent the chain from slipping off (e.g. when turning). Also it should be avoided designing machines with too many bearings and cog wheels. Finally, it should also be possible to disengage the fertilizer and seed distributor by means of a clutch when the end of the row is reached.

Most seeders have either a horizontally or diagonally mounted dispensor. The sloped attachment of the hole disk, as with the Super Eco, is advantageous for sensitive seed such as groundnut (Wieneke and Friedrich, 1983). The dropping distance of the seed should be kept to a minimum, in order to achieve a most possibly exact depositing of the seed. The planting wheel can be designed as a hole disk, seed plate or spoon-fed mechanism. The latter are less sensitive towards calibration errors. For small- kernel seed (e.g. sorghum and rice) only pocket drilling can be achieved with precision seeders.

On the whole, the inadequate precision of the distributor mechanism is criticized. The poor design of the dispensor frequently causes damage to the seed. In the survey fault is found with the manufacturing quality of the hole disk and the conveyor wheel (cast iron), and polishing is suggested as a solution. A figure from Brazil states that 5 - 10 % of the seed is damaged by the spacing wheel. This is confirmed by Casao at al. (1987), who record a 5 % damage rate with maize. Thus, the spacing wheel as well as the seed knockout and dispensor should be as smooth as possible (made of plastic), in order to avoid damage to seed. The holes of the planting wheel should be slanted from below to prevent blockage of the seed. Erroneous mounting can be hindered by means of the recessed design.

Faults have been described for both Brazilian seeders and the Super Eco (Casao et al., 1987; Starkey, 1981). This also certainly occurs with artisanally manufactured planting wheels. The seed of smallholders is often not calibrated. Frequently, the appropriate planting wheels are lacking for certain crops, and their thickness is sometimes not uniform. Many farmers have severe difficulty adjusting the implements.

The hole disk of Brazilian seeders must be replaced by a cogged wheel necessary for transporting to plant cotton. The expulsion takes place sideways by means of a fluted roller. For groundnuts a covering lid is inserted.

The Tamba developed in Senegal for the sowing of non-defibered cotton seed has a distribution mechanism consisting of a stirring apparatus in a housing and a fluted roller under the seed container, which regulates the expulsion. It deposits the seed in pockets, but has been poorly assessed because of fluctuations of seed density (Havard, 1988a). Seeders are delivered equipped with various planting wheels. The Brazilian made HMC (figure E 57) is normally offered with 5 hole disks having 4, 5, 6, and 10 holes, a disk without holes, which can be fitted by the owner, and the dispensor for cotton. The apparatus for groundnut seeding must be ordered as an accessory.

Opening furrows, depositing and covering of the seed

The furrow should be pointed at the bottom in order to prevent rolling of the kernel in the furrow. Sabre-type shares sometimes disk shares, are used to open the furrows. In hard soils hoeing shares tend to glide less than gently curved sabre-type shares (Havard, 1988a). Disk shares are better suited for fields having roots, over which they can glide. However, they can become damaged by stones. As applies for all turning parts, they are expensive. The Triton seeder from South Brazil is the most reasonably priced implement on offer, according to information provided by the farm machinery outlet Regia; they are equipped with double disk shares and have eliminated the front wheel (figure E 55). The Super Eco from Senegal has a knife coulter to facilitate the penetration of the furrow opener. It was however not accepted by the farmers (Havard, 1988a).

With the occurrence of larger clods or vegetation residues the furrow opener can become clogged. Wide shares heap up a considerable amount of earth and organic mass. To improve the work prior furrow breaking is recommended. In some cases clogging can be a result of farmers wanting to sow immediately following a rain as is done in manual operations (v.d. Decken, 1989).

Substantial fluctuations in the precision of depositing the seed have been observed with the seeders. In a trial with Brazilian seeders, average deviations of 40 % were determined in the rows, approximating that of dibbling. The depositing depth is generally adjusted with the aid of the press roller.

However, on some implements the depth adjustment is only possible by means of the point of attachment (e.g. Safim, southern Africa). Aside from the dibbling seeder (Grazia, figure E 52) most implements can maintain a maximum depositing depth of 4 cm (Casao et al., 1987). The Super Eco (figure E 53) is also considered inadequate, since it is not suited for sowing seed deeper, e.g. millet at 6-8 cm on dryland. The regulation of the depositing depth is accomplished by adjusting the furrow opener.

Frequently the farmers get the furrow opener welded, so that it does not become lost (Havard, 1988a). Generally, reports are often heard that serious problems occur with the depositing depth of the seed. Seed covering scrapers and press rollers take care of covering the furrow with earth and assure good soil resealing. Thereby, the moisture supply is sufficiently guaranteed. The seed covering scrapers must cover the furrow properly with soil without allowing organic material to be drawn in or stones to be transported into the furrow which depends on the mounting position. They should be easy to adjust for height and angle (as with the Sans models, figure E 54) in order to adapt to the field conditions at all times and to prevent clogging. The Super Eco is equipped with seed covering scrapers in the form of duckfoot shares, which simultaneously achieve weed control. Faulty function of seed covering scrapers is often mentioned in regard to clogging and poor covering of the soil, especially if they are attached too close to the ground and the press roller.

The shape of the press roller is important: it should provide for optimal covering and resealing by means of the shape of the wheels; larger wheels are preferred in order to avoid clogging. Generally, the press rollers are only adjustable for regulation of the depositing depth.

Application of chemical fertilizer

All implements, including the Super Eco and parallel developments in neighbouring countries, are offered with attachments to spread chemical fertilizers (2/3 of all the cases). Thereby a more precise spreading in comparison to hand spreading is achieved, a saving of fertilizer and more rapid access by the plants. A further aspect is easing the workload. The farmers however must be able to precisely adjust the dosage.

Seeders that can simultaneously spread fertilizer are generally longer and heavier, whereby the machine then becomes clumsier to handle. Fertilizer application occurs through an auger or stirrer and dispensor. Separate depositing of seed and fertilizer is important, so that the seed does not "burn", as has been reported form Zambia.

There are essentially three solutions for separation. The best separation is achieved if the fertilizer is deposited with a detached share from the side (Baldan, Safim) or is placed under the seed. In the latter case usually a second deeper share precedes the first following the same line (Sans). On a dibbler a second, complete planting wheel with a beak tip is attached, which takes care of a clean separation (Grazia). On implements with two shares, especially if there is a staggered arrangement, more draft power is required and risk of clogging increases.

On some implements (e.g. HMC, Triton, Tatu, figure E 58) only one share is available for sowing the seed. The fertilizer falls in front of the seed onto the ground and it is subsequently worked in with the share. This is considered to be an adequate solution (Casao et al., 1987).

In many countries the dissemination of chemical fertilizers is a component part of the extension services. If they are applied however, in practice it is often found that seed and fertilizer are deposited in separate work operations. This can be attributed to common cropping practices as well as to the weight of the seeder.

Material and design

High weight (e.g. Tatu) as well as a high point of gravity (Baldan) make the handling of the implements awkward, especially on slopes and in small plots. Seeders with a light weight can easily be lifted when they become clogged. There is however a minimum weight originating from the seed and fertilizer, for example the seed and fertilizer hoppers of Tatu implements weigh 13 and 23 kg, respectively. The average weight of the implements occurring in the survey was 43 kg. The seven implements tested in Brazil weighed between 53 and 72 kg. If the implement is too long it is difficult to handle on hilly terrain having curves (HMC). Single-row implements have a width of 40 to 58 cm (Tatu). Two-wheeled implements are wider, e.g. Citra = 96 cm (figure E 59).

All bearings should have greasing points to prevent sliding of heavy-geared drive wheels and thus a disruption of the seeding operation (Casao et al., 1987). The hoppers should be easily removeable. This is necessary for emptying, adjusting (exchange of spacing wheel) and cleaning operations. Especially implements which spread fertilizer should be cleaned regularly to prevent corrosion, which is a frequently occurring problem. This could be solved by manufacturing the part out of other material (e.g. fiberglass), but it would entail a higher cost and the new material would create additional difficulties for the artisans.

In the survey numerous problems were listed regarding unsatisfactory design, negligent fabrication and maintenance. The material is predominantly considered to be of medium to poor quality and the high weight is criticized. The bearings cause further problems. Poor assembly causes cumbersome access to bearings, missing sealings lead to the breakdown of bearings, especially due to sand.

In some cases the bearings can only be replaced by the manufacturer. The risk of down-time is high: breakage of chains, gear parts and bolts, wear to gear wheels in the drive mechanism, loose bolts and loss of individual parts were mentioned in the survey.

The required draft power is dependent on the weight and the parts which come into contact with the soil. The Super Eco requires 20 kp on sandy soil and 30 kp on more clayey soils (with coulter, furrow opener and duckfoot shares) (Havard, 1988a). In a test with Brazilian seeders measurements of 20 to 30 kp were also recorded. The Grazia dibbler required the second-lowest draft power after the HMC implement, which only has one share for seed distribution. (Casao et al., 1987)

From a technical point of view an improvement of seeders, the design of which has not been further developed for many years, could be achieved by a lighter construction with modern materials. At the same time, demands on seedbed preparation could be reduced. As a result a direct drilling machine could be created that would work more independent of the field conditions. It appears that such an implement however could not be easily marketed in sufficient quantities, given today's problems which the farmers have regarding the mechanization of the seeding operation, especially due to the high investment cost.

6.2.2.4 Discussion

On the whole, seeders are seldom utilized, only in 30 cases in our survey, including the cases of very occasional use. Limiting conditions for their employment are elucidated in the following assessment (in brackets the number of instances):

- Economic reasons rank first, such as too high price (17) and too low labour and productivity distribution margins (14) (available labour force, labour savings too small or cropping area not sufficient).

- Limited conditions for utilization due to topography (8), unsuited soils (e.g. too clayey and sticky in Zambia and Ethiopia) (4), mixed cropping or lack of row cropping (6), obstacles on the fields (6) and poor seedbed preparation (3) rank second.

- Third follows the lack of adaptation to the agricultural farm system, including the fact that the implement is not known or not obtainable or it does not have any tradition of use or that animal traction is still in the introductory phase (9).

- Finally, it was mentioned that the use of seeders is difficult for the farmers (adjustment, handling), little know-how is available or more extension services are necessary (5). In fields with roots or stones and much organic matter (fallow and harvest residues) seeders do not function properly. The seedbed must be prepared well for most implements, if the soil is not very light. Calibrated seed is necessary for the precision seeder, which hardly applies for the smallholders. Patchy and double sowing can be caused thereby. In addition, inadequate quality of the implements in terms of the work result is often recorded. In comparison to other implements there is a higher number of worn out parts and points to repair; this requires greater preparedness of the farmers to carry out maintenance and more experience by the artisans.

Multi-row seeders have hardly found acceptance in the praxis. They require a greater investment. A better seedbed preparation is necessary and their handling is rendered more difficult due to the great width and weight. An entirely exact seeding in rows is only required, on the other hand, where multi-row weed control is being carried out.

In the regions examined, seeders are primarily being utilized under the following conditions:

- In regions having a short vegetation period such as Mali and Senegal seeding represents a work peak and rapid sowing is necessary, which can in part take place by direct sowing. This also allows an expansion of the cropping area.

- Their acceptance is particularly high for the cropping of cotton and groundnuts, for which they were partially developed. If the investment does not pay in terms of a better yield, the farmers cannot pay the high price. The market production must therefore be quite advanced.

- The supply of accessories (e.g. hole disks) and spare parts must be guaranteed by an industrial and artisanal structure.

Animal-drawn seeders have been, due to their limitations, only disseminated in a few countries such as Brazil, Senegal, Mali and southern Africa.

6.2.3 Fertilizer applicators

In some countries such as Brazil fertilizer applicators are increasingly being used, independent of the sowing time. They are appropriate for the spreading of chemical fertilizer, dry and organic manure. In part this is combined with furrow breaking prior to seeding. Some implements have two applicator tubes in order, for example, to apply nitrogen directly to the plants when passing between the rows. The applicator mechanism consists of augers or stirring devices with spreaders.