A seed drill meters seed at a set rate into narrow rows and covers it at a uniform depth, using a fluted roller or a sponge rather than counting individual seeds. Seed drills suit close spaced crops such as beans, soya, small grains and fodder grasses, where many rows have to be covered quickly. What you set on a drill is kilogrammes per acre, not the gap between one seed and the next.
What a Seed Drill Does With Seed in the Row
Start with a bean field, because that is where the machine earns its place in Uganda. Bush beans go in at 50 cm between rows and 10 cm within the row, one seed per hole, which works out at roughly 80,000 plants on an acre. Ugandan bean guidance assumes three people to a marked line, splitting the digging, the fertilizer and the seed between them, and repeating that cycle eighty thousand times over. Nobody does it evenly for a whole acre.
A seed drill does not try to. It abandons the idea of placing each seed and instead controls how much seed leaves the hopper per metre travelled. Inside, a fluted roller turns in the base of the seed box, driven by a ground wheel through a chain and sprocket, and the amount discharged depends on how much of the flute is exposed to the seed. Open the flute further and more seed flows. The seed drops through delivery tubes into furrows cut by openers, and a wheel or disc behind each opener closes the slot and presses soil against the seed.
Four jobs happen in that one pass: metering a predetermined quantity of seed, opening a furrow to the right depth, delivering the seed into that furrow, and covering it. Most drills add a second hopper and a second set of tubes so granular fertilizer goes down beside the seed at the same time.
Notice what is absent. Nothing in that mechanism knows whether the next centimetre of row gets one seed or three. The rate is right and the depth is even; the spacing within the row is a statistical outcome. Engineering reviews of conventional drills say so directly, listing the reduction of within row variability in seed rate as an outstanding design problem rather than a solved one.
Why a Seed Drill and a Maize Planter Are Not Interchangeable
Sellers use the two words loosely. The machines are not the same, and buying the wrong one is an expensive way to find out.
The difference sits in the metering mechanism and in what it can promise you.
| Metering type | What it sets | Seed it suits |
|---|---|---|
| Fluted roller | Weight per acre | Cereals, legumes |
| Sponge | Weight per acre | Fine, light seed |
| Inclined plate | Seeds per station | Maize, large seed |
| Pneumatic | Seeds per station | Tiny, irregular seed |
The top two rows are drill mechanisms and the bottom two are planter mechanisms. Extension guidance on grain drills is candid about the trade: a machine that meters seed by flute or sponge cannot place it as accurately as one that counts it out. Set against that, the same guidance points out that drills are cost effective for establishing close spaced crops and do place seed at a uniform depth, so long as the depth control and furrow closing wheels are properly adjusted and maintained.
Row width follows from the mechanism. Conservation agriculture training material puts drill rows at around 15 cm to 20 cm and planter rows at roughly 50 cm to 100 cm. Ten or twenty narrow rows behind one machine is what a drill is for. One or two wide rows with a counted seed at a measured interval is what a planter is for, and our companion page on maize planters and plant population works through why maize in particular cannot be handed to a drill.
Ugandan Crops a Seed Drill Suits: Beans, Soya and Small Seeded Crops
The test is simple. If the recommendation you follow is written as kilogrammes per acre and a row width, a drill is the right machine. If it is written as a within row distance and a seed count per hole, it is not.
| Crop | Row spacing | Seed rate per acre |
|---|---|---|
| Bush beans | 50 cm by 10 cm | 25 to 30 kg |
| Soya | 50 cm rows | About 8 to 10 kg |
| Maize | 75 cm by 25 cm | 10 kg |
Beans are the clearest case. The Ugandan recommendation for bush varieties is 50 cm by 10 cm at one seed per hole, or 50 cm by 20 cm with two seeds, both giving roughly 80,000 plants per acre from 25 to 30 kg of seed. Nobody is asking a machine to space individual bean seeds 10 cm apart; they are asking it to lay down 27 kg an acre at 5 cm deep in straight 50 cm rows, and that is a drill's exact job. The bean spacing and seed rate per acre page carries the agronomy.
Soya sits on the boundary. The Ugandan recommendation is 50 cm rows with 10 cm to 25 cm between plants, sown 2 cm to 5 cm deep. At the wide end of that range a plate planter can singulate it; at the narrow end a drill is faster and loses nothing. Worth flagging: the ministry's soybean extension manual gives the seed rate as 20 to 25 kg per hectare in its agronomy section and as 20 to 25 kg per acre in its own budget table, and those cannot both be right. The hectare figure converts to roughly 8 to 10 kg an acre, which is what the 50 cm spacing supports, so treat the per acre version in the budget table as an error and calibrate against the plant population your own spacing implies rather than against either printed figure.
Beyond those two, the drill's natural territory in Uganda is small seeded and densely sown crops: sesame, upland rice, sorghum and finger millet, and fodder and pasture grasses where the seed is light and the stand needs to be thick. For those, published seed rates vary widely with variety and with seed quality, so calibrate to the rate your own extension officer or seed supplier gives you for the variety in the bag, rather than to a generic figure. Where the figure you are handed is per hectare, or per metre of row, our seed rate calculator will put it into whatever unit your drill is set in.
Row Spacing: Why a Drill Runs Narrow
Narrow rows are not an accident of design; they are the reason the machine exists. A crop at 80,000 plants an acre has to put those plants somewhere, and if the rows are wide the plants have to crowd within the row, which is the worst way to arrange them. Spreading the same population over twice as many rows gives every plant a rounder patch of soil to draw from, shades the ground sooner, and starves weeds of light earlier. Guidance on weed management in legumes lists higher seed rates in narrow rows as a cultural control in its own right.
Most drills let you change row width, within limits. On a tractor drawn unit, working width is simply the opener spacing multiplied by the number of openers, and you change it by moving openers along the toolbar. On the multicrop units supplied with two wheel tractors, four openers at 20 cm handles a small grain, and maize row width is reached by removing the two centre openers altogether and measuring what remains. Animal drawn drills built for intercropping typically adjust between about 20 cm and 45 cm by moving one or two cutter type openers on a detachable bar.
One practical point that costs seed every season: fit or improvise a row marker. A drill with no marker leaves the operator guessing where the last pass ended, and overlapping passes double the seed rate in a strip while the next gap gets none. A trailing chain, a scribed line or a simple arm set at the working width solves it.
Seed Rate Per Acre Is the Number You Are Setting
Since a drill sets weight rather than spacing, the weight has to be the right one, and the figure on the recommendation sheet is rarely the figure you should pour in. Two corrections come first.
Our notes on what a germination percentage on a seed label means go through the label itself. The point for a drill operator is that germination and purity change the loaded weight, which changes the machine setting, so the calibration has to be redone whenever the seed lot changes and not just when the crop changes.
The Seed Chart on the Lid Is Only a Starting Point
Almost every drill carries a rate chart, often printed on the underside of the seed box lid, matching a lever position to a rate for a list of crops. Use it, and do not trust it.
Extension guidance is explicit that these charts give a good first setting but may not be accurate, and it names the reasons. Seed size and shape differ between varieties of the same crop and sometimes between lots of the same variety. Seed coatings and treatments change how kernels slide past each other. Bulk density differs. And sooner or later you will sow something the chart does not list at all, such as a grass and legume mixture for a fodder plot, or a variety released since the machine was made.
Wear is the reason a chart drifts even on a familiar crop. Metering parts slowly lose their edge, so a lever position that delivered the right rate three seasons ago delivers less now. On hired machines the problem compounds, because you do not know what the last user set, nor what they left behind in the seed box. Calibration each season is the only honest fix, and on a rental unit it is a first pass check rather than a formality.
Calibrating a Seed Drill Over a Measured Distance
The principle is to reproduce a known area of drilling without going anywhere, weigh what comes out, and scale it up. Work in acres, since that is the unit every Ugandan recommendation uses.
Two wheel tractor training uses a 30 m run for drilling and a 50 m run for precision planting, and either length works so long as you are consistent. Longer runs average out wheel slip and metering irregularity; shorter runs are quicker to repeat while you hunt for the setting. Do the hunting in the yard and the confirming in the field.
Mixtures are calibrated exactly as a single crop is. Two things help. Mix thoroughly and weigh each component for the whole area first, because a partly mixed box meters the components in the wrong proportion as the level drops. And start from the lever setting for the largest seeded component, since mixtures usually pack more densely than a single species and a setting that is too open is easier to notice than one that is too closed.
Checking Each Opener, Not Just the Total Seed Rate
A drill can pass a calibration and still ruin a field, because total output says nothing about how that output is shared between openers. Collect the seed tube by tube, into a separate bag or tin for each, and weigh them individually.
The working tolerance from extension guidance is ten percent: if any one opener delivers a weight more than about ten percent away from the average of all of them, the metering mechanism needs attention rather than adjustment. A roller worn on one side, a chain with a stiff link, a drive shaft out of true, a partly blocked tube, all of them show up here and nowhere else.
The check also finds the openers delivering nothing at all. Before any calibration, turn the wheel until seed appears from every tube. Any tube that stays dry is kinked, crushed or blocked, and the commonest blockages found on drills that have been sitting are old seed from a previous crop, straw, and spider webs. On a hired machine, assume all three until you have looked.
Seed Depth and Down Pressure for Small Seeded Crops
Sowing too deep is the largest single cause of drilling failures, and small seeded crops have almost no reserve to spend on a long climb. A useful rule of thumb from grain drill guidance puts seeding depth at roughly three and a half times the seed diameter, which for most small seed lands between 2 cm and 3 cm. Ugandan bean guidance gives 5 cm for beans, lightly covered, and the ministry's soybean manual gives 2 cm to 5 cm with the shallower end recommended for heavy clay soils and for wet, cold conditions. Where sources differ like this, the deciding factor is soil moisture: shallower into a moist, heavy seedbed, deeper into a drying, light one.
Depth is held by the gauge or depth control wheel rather than by the opener setting alone. Tractor drawn drills place a depth wheel immediately behind each disc opener so that the wheel follows the ground the opener is cutting, which keeps delivery depth even across ridges and hollows. That is the part to inspect on a used machine, because a seized or badly worn depth wheel leaves you with a drill that sows at whatever depth the terrain decides.
Down pressure needs restraint. Use no more than is needed for consistent seed to soil contact. Excess down pressure in wet soil smears the furrow wall and compacts the slot, which is a poor place for a seedling to start, and it is the most common overcorrection made after a shallow first pass.
Verify depth rather than assuming it. Plant a test strip and dig back to the seed in several places. There is an old trick worth using on small seed you cannot easily find in loose soil: spray paint a small quantity of the same seed a bright colour, let it dry hard, mix it through the seed in the box above each outlet, and then look for the coloured seeds in the opened row. They are easy to see and they tell you the real depth rather than the intended one.
Where a Seed Drill Blocks, Thins or Over Seeds
Drill faults show up as patterns in the emerged crop, and each pattern points at a different part of the machine.
Trash is the fault line. A drill built for a clean seedbed uses a shovel type furrow opener, which is cheap and which jams solid in anchored stubble. Machines meant for drilling into residue use an inverted T opener that tears through anchored stubble, or a double disc opener where the leading disc deflects residue so the pair can cut a clean V into the soil. Offset discs of different diameters do this with less weight per row, which matters behind a small tractor. If your fields carry residue and your drill has shovel openers, the honest answer is that the machine will not do the job and no amount of adjustment will make it.
Hand, Animal Drawn and Tractor Drawn Seed Drills
Drills exist at every power level, and the realistic entry point in Uganda is far below a tractor.
A manually operated seed drill is a seed hopper over a fluted metering device, driven by a ground wheel through a chain and sprocket, with a shovel type furrow opener and handlebars for the operator. One person works it, and published field capacity is about 0.3 to 0.4 hectares a day, so roughly three quarters of an acre to an acre in a working day. It is used a great deal for sowing small seeded oilseeds and for inter row sowing inside a standing crop, which is exactly the fiddly work that hand planting does badly.
Animal drawn drills add capacity without adding fuel. A typical intercropping unit carries a seed hopper and a fertilizer hopper, both on fluted roller metering, hitched so the beam height can be set for different animals, with one or two cutter type openers on a detachable bar giving row widths around 20 cm to 45 cm. A traction wheel drives the metering shafts and doubles as the depth control and the press wheel over the seed zone. Where oxen are already kept, this is the cheapest genuine increase in drilled area available.
Two wheel tractors sit next. The versatile multicrop units supplied with single axle tractors run in either a drilling mode or a precision planting mode, and switching between them means shutting off the metering inlets you are not using with the blanking plates that come with the machine. Read the caution in the training material seriously: closing an inlet loosely, or pulling off a delivery pipe and assuming the outlet is shut, wastes seed and fertilizer through the whole pass. These units want more than 12 horsepower behind them, which is worth checking against whatever tractor you have access to. The power tiller and single axle tractor notes cover the power unit.
Tractor drawn drills scale up sharply. Mechanical units of thirteen to twenty one rows sit behind tractors of around 65 horsepower, with hoppers measured in hundreds of litres and fertilizer metered by a worm shaft distributor discharging behind the disc openers. At that size the machine is a service business, not a farm tool. Smaller six row seed and fertilizer drills about 1.2 m wide are the more realistic tractor option on Ugandan holdings, and tractor implements and how they mount covers the hitch side of that decision. A full view of the machinery options sits in our farm machinery guide for Ugandan farmers.
The Seedbed a Seed Drill Depends On
Drills are less forgiving of rough ground than hand sowing, for one reason: a 2 cm to 3 cm target depth has almost no tolerance. On a cloddy surface the opener drops into every hollow and rides over every clod, and a seed meant for 3 cm ends up at 1 cm in one place and 6 cm in the next. The rate stays perfect and the crop comes up over a fortnight.
Closing is the second problem. A press wheel can firm loose tilth over a small seed; it cannot make a clod close a slot. Bean guidance from Ugandan work is direct that the crop needs a fine seedbed for proper root growth, and adds the part farmers notice most, which is that a well prepared seedbed cuts the number of weedings needed later.
In practice that means ploughing followed by harrowing, not ploughing alone, and it means running the drill across a levelled surface rather than over plough furrows. Our comparison of the disc plough against the disc harrow explains which pass produces which result. If you intend to drill into residue instead, the money belongs in the openers rather than in extra tillage, and you should buy the machine for the residue you actually have.
Frequently Asked Questions
What does a seed drill cost in Uganda? No reliable published Ugandan price range exists for any class of drill, and quoting one supplier's figure would mislead you, since consignment, capacity, opener type and the exchange rate all move it. What you can cost precisely is the alternative. Hand planting labour in ministry crop budgets runs at roughly UGX 60,000 an acre for opening holes plus about UGX 20,000 for the planting itself, so call it UGX 80,000 an acre, and bean planting at 80,000 stations an acre sits at the expensive end of that. Work out how many acres you sow each year across both seasons, multiply by that labour figure, and use the answer as the ceiling on what a machine can be worth to you. Our breakdown of the cost of bean farming sets planting labour against the other lines on the budget, and where to buy bean seed covers the seed side. Then get current quotes locally on that basis.
Can I use a maize planter as a seed drill, or the other way round? Partly, in one direction. Multicrop units sold with two wheel tractors are built for both jobs and switch between drilling and precision planting by changing openers and blanking off inlets. A dedicated maize planter with plate metering will not drill a close spaced crop, because it cannot deliver a continuous rate and its narrowest row setting is still too wide. A dedicated drill will physically sow maize, but it gives you kilogrammes per acre rather than a seed every 25 cm, which for maize is the wrong control to have.
How often do I need to recalibrate? Every crop, every seed lot, and every season. Seed size, shape, coating and bulk density vary between varieties and even between lots of the same variety, and metering parts wear. A hired drill gets calibrated before every single use, because you have no idea what the last operator set. Once a machine and a seed lot are settled, a quick field check of seed per metre on the headland is enough between fields.
Can a drill sow a pasture or fodder seed mixture? Yes, and this is one of the jobs a drill does far better than hand broadcasting, because it puts light seed at a controlled shallow depth instead of leaving most of it on the surface for birds and sun. Calibrate the mixture as a single crop, mix it thoroughly beforehand, and start from the setting for the largest seeded component. Expect the setting to be lower than for either component alone, since mixtures pack more densely in the box.
Why did some of my rows come up thin when the seed rate was right? Almost always an individual opener rather than the rate. One blocked delivery tube, one metering unit not turning, or one worn roller delivering less than the rest will give you a thin or empty row beside perfect neighbours. Weigh the output of each tube separately at calibration: any opener more than about ten percent off the average of all of them needs repair. Clear every tube before each use, because old seed, straw and spider webs are the usual culprits.
Does drilling save seed compared with broadcasting? It saves seed and it saves more than seed. Broadcasting relies on a high rate to compensate for seed that never reaches useful depth, and the seed that does germinate emerges over a long, ragged window. Drilling places a known weight at a known depth in a known row, which lets you sow the recommended rate rather than an insurance rate, gives even emergence, and makes weeding, spraying and harvesting down a straight row possible. Even placement producing even emergence is the mechanism under all of that: where a crop breaks ground across a fortnight, the first plants up shade the last and the last never catch them.
Is a drill worth it if I only grow one acre of beans? Not to own outright, on those numbers. A hand operated drill covering about an acre a day, bought by a farmer group or by one service provider and worked across a village, is the version of this that pays. The other honest answer is that on one acre the cheapest fix is not a machine at all: a marked planting string, a decided row width and a disciplined team will get you closer to 80,000 even plants than an uncalibrated drill will.
If you are pricing a drill, compare several equipment suppliers on one written specification rather than on a headline figure. State the number of openers and the row spacing you need, the opener type your fields call for, whether you want a fertilizer hopper, and ask whether a rate chart and blanking plates are included. Ask two more questions that matter more than the price: which wear parts they hold in stock, and who services the machine locally. Prices move with each consignment, so confirm the current figure at the point of purchase, and if you can, arrange to watch the same model calibrated and working before you commit to buying one.