🌿 Land Preparation, Spacing and Intercropping

Most farmers think of land preparation and weeding as two different jobs done at two different times. The framework this course follows treats them as one continuous process, and that reframing is worth more than any single technique in this module.

The IITA six-steps cassava weed management framework sets out the operations in order:

1. Site selection.
2. Slashing existing vegetation.
3. Land clearing, mechanically or with herbicide.
4. Ploughing and ridging.
5. Planting, with pre-emergence herbicide application where that is used.
6. Post-emergence weed control, manual or chemical.

Look at where planting sits in that list. It is step five of six. Four operations happen before a stake goes in the ground, and all four are weed-control operations as much as they are soil-preparation operations.

Why does the framing matter so much in cassava specifically? Because of the timing problem Module 2 established. Cassava's canopy closes only at roughly 20 to 24 weeks after planting, and the crop is most susceptible to weed encroachment in the first 10 to 16 weeks of cultivation. That leaves a long window in which weeds face no competition from the crop canopy for light. The plant is not weak; it is slow to cover the ground.

So the weed pressure your field will face during those critical weeks is largely decided before planting day, by how thoroughly you cleared, what you left behind, and what seed bank and root fragments you buried or exposed. A field entered with a half-cleared weed problem does not give you a fair fight during the critical period. It gives you a fight you were already losing on planting day.

And the stakes are quantified. A properly weeded cassava farm is reported to achieve 30 to 50 percent greater root yield than a poorly weeded farm. That is a large, sourced range, and it alone justifies the labour or herbicide cost of weeding in almost any market condition. Farmers trained under the same six-steps programme achieved more than 20 tonnes per hectare against a cited Nigerian national average of 9 tonnes per hectare, though that compares a trained and supported cohort with a national average, and the trained group also received improved variety, spacing and fertiliser advice in the same programme. Treat it as the ceiling good practice can reach, not the guaranteed result of weeding alone.

Now take each step seriously in turn.

Site selection is a real decision and not a formality. You are choosing drainage, slope, previous cropping history and distance from the road and from your processing point. Module 2 warned about continuous cassava on the same land mining potassium. Site selection is where you act on that, by rotating rather than replanting the same block a fifth time.

Slashing existing vegetation cuts the standing growth down and makes everything after it possible. Do it early enough that regrowth can be dealt with before planting rather than after.

Land clearing removes what slashing left, whether by hand, machine or herbicide. Where herbicide is used, product choice, registration and safe-use rules are set by your national authority. Ask your extension service or plant-protection regulator which products are registered for this use in your country, at what dose, and with what protective equipment. Never take that advice from a seller with stock to move.

Ploughing and ridging prepares the seedbed and is covered in Lesson 2, because whether you ridge at all is a soil decision.

Planting with pre-emergence herbicide where used is the point at which a chemical programme, if you run one, is set up. Again a regulator question.

Post-emergence weed control is the follow-through, and Module 6 covers the timing in detail.

The practical discipline is a calendar. Write your intended planting date. Then work backwards and put dates on slashing, clearing and ridging, allowing enough time between each that regrowth is handled before the next step. Farms fail this not through ignorance but through compression: everything gets done in the same fortnight because the rains arrived, and the weed control that should have happened in step two is still waiting to be done in week ten, when it costs yield you cannot recover.

There are three ways cassava is commonly established: on ridges, on mounds, or on the flat. The choice is not tradition and it is not preference. It follows from your soil and your water.

The reported rule is straightforward. Cassava is typically grown on ridges or mounds in areas with heavier or wetter soils, to improve drainage and ease of harvest, and on the flat in lighter, well-drained soils.

Take the two reasons separately, because they are genuinely different benefits and you may care about one more than the other.

The first is drainage. A cassava storage root sitting in waterlogged soil is a root at risk of rot, and heavy soils hold water after rain in a way that light sandy soils do not. Raising the planting position above the general soil surface lifts the root zone out of the standing water. On a heavy clay plot where puddles sit for a day after rain, that lift is the difference between a crop and a loss.

The second is ease of harvest, and this benefit is badly under-appreciated because it does not show up until month twelve. Cassava harvesting is heavy work. Roots have to be lifted whole out of the soil without breaking, because a broken root starts the deterioration clock immediately and Module 2 established that fresh roots begin to spoil within 48 to 72 hours of harvest. Loosened, raised soil in a ridge or mound lets the root be lifted rather than dug out and cut through. On hard flat ground in the dry season, a substantial share of your roots can be damaged during harvesting.

And harvest labour is real money. A single FAO compendium figure puts combined harvesting and processing labour at approximately 721 man-hours per hectare, though that is a single cited figure rather than a universal constant and depends heavily on whether harvesting is manual or mechanised and on the yield per hectare. Anything that makes lifting easier acts on a large labour cost.

So how do you decide for your own plot? Observe rather than guess, and observe at the right moment.

Walk the plot the day after heavy rain, not a week later. Note anywhere water stands, anywhere the soil stays sticky, and anywhere it has already drained. That map is your answer. Standing water or heavy sticky soil points to ridges or mounds. Fast-draining light soil points to flat planting being acceptable, and flat planting is less work.

Also look at slope. On sloping land, the direction you run ridges matters, because ridges running straight down a slope channel water and accelerate erosion, while ridges running across the slope slow water down. On any noticeable slope, run ridges across it rather than down it.

And remember what a plot can be. Fields are rarely uniform. It is entirely legitimate to ridge the low wet corner and plant the higher, lighter part flat. The rule is a response to soil conditions, and soil conditions vary within one field.

One caution about copying your neighbours. If everyone around you ridges, that is real local knowledge and probably reflects real local soil, so take it seriously. But check that they are ridging for a reason that applies to your plot and not because their fathers did, and check whether their soil is actually the same as yours. Ridging costs labour or machinery time. If your soil is light and free-draining, you may be paying for a benefit you do not need.

Ridging also connects directly back to Lesson 1. Ploughing and ridging is step four of the six-steps framework, sitting between land clearing and planting. It is not only preparing a seedbed. It is burying weed regrowth and giving you a clean surface to plant into, which means the timing of ridging relative to planting matters. Ridge too far ahead of planting and weeds re-establish on your fresh ridges before the crop is in. Ridge and plant close together and the crop gets the clean start it needs for the critical 10 to 16 weeks.

Finally, whichever method you choose, record it alongside the sprouting percentage and yield for that plot. Two seasons of records comparing your ridged corner against your flat corner will tell you more about your own land than any general rule can.

A stake can be planted three ways: vertically, at a slant, or horizontally. All three are reported in the literature and all three are used in practice. Here is what is actually sourced and where the honest limits of the evidence sit.

One guide recommends vertical planting in wetter conditions and slanted or horizontal planting where rainfall is lower.

The reasoning given is that vertical planting keeps the cutting's stored moisture and buds positioned differently relative to the drying surface layer, while horizontal planting spreads sprouting points along the whole length of the cutting, which can help in moisture-limited conditions by increasing the chance that at least one bud reaches viable moisture.

Now the important qualification, and this course will not skip it. The precise physiological mechanism was not further sourced in this pass. So treat that reasoning as reported field practice with a plausible explanation attached, not as a proven mechanism you can extrapolate from. The recommendation itself, vertical where wetter and slanted or horizontal where drier, is what is reported. The explanation is how the source explains it.

Why does that distinction matter to you? Because a proven mechanism can be extended to new situations and a reported practice cannot. If you knew exactly why horizontal planting helps in dry conditions, you could reason about whether it also helps on a particular soil type or at a particular depth. Without that, you can follow the reported practice and observe your own result, which is what Lesson 6 asks you to record.

On depth, the reported figure is 5 to 10 centimetres of the cutting below the surface, with most of the cutting left exposed above ground in the vertical and slant methods.

That second half surprises people. Most of the stake stays above ground. A 25-centimetre stake planted vertically with 5 to 10 centimetres buried leaves roughly 15 to 20 centimetres standing in the air. Farmers who bury stakes almost completely, thinking deeper means safer, are working against the reported practice.

Hold the two rules together, because they interact. Deeper burial reaches moister soil, which argues for depth in dry conditions. But burial also puts the buds where they must push further to emerge, and the sourced depth range stops at 10 centimetres. Within that range, plant nearer 10 centimetres when the surface is dry and nearer 5 when the soil is moist, and do not exceed the sourced range on the theory that deeper must be better.

Orientation, in the sense of which end is up, is separate from angle and it is absolute. A stake has a top and a bottom, and planted upside down it sprouts poorly or not at all. Module 4 gave you the working habit: cut the bottom square and the top at a slant so that orientation stays visible on the pile. On planting day, that habit is what protects a whole batch from being lost by a helper who does not know to look.

The horizontal method is different enough to describe on its own. The stake is laid in a shallow furrow along its length and covered. Sprouts emerge from multiple nodes along the buried stem. It uses more of the stake's node positions, and it removes the upside-down risk entirely, since there is no up. It is harder to weed around precisely, and the emerging shoots are more spread out, which changes what your field looks like at week four.

Whichever method you use, plant into moist soil. The whole of Module 4, Lesson 3 was about a 20 percent moisture loss costing 50 percent of sprouting. A well-cut, well-stored stake planted into dust is still a stake asked to survive on its own reserves until rain arrives. Time your planting with the rains, not with your convenience, and if you must hold stakes waiting for rain, hold them bundled upright in shade rather than in the ground.

And measure your result. Count sprouts at four weeks as a percentage of stakes planted, and write it beside the method you used and the soil moisture at planting. Three seasons of that record is a genuine local answer to a question the literature answers only in general terms.

Spacing decides how many plants you have, how fast the canopy closes, how easy the field is to weed, and how much each plant has to work with. You set it once, on planting day, for the whole cycle.

Here are the reported figures, and note that they vary by source and by whether the crop is grown as a monocrop or intercropped.

For monocrop cassava, 1 metre by 1 metre is commonly cited. One grower guide gives a higher-density alternative of 1 metre by 0.8 metres. An IAEA guide gives a different shape of the same idea: 75 to 100 centimetres between rows or ridges, and 50 to 75 centimetres between planting holes within the row.

Notice that the IAEA range is tighter within the row than the 1 by 1 figure. There is no single correct number here, there is a reported band, and the sources sit at different points within it.

Now the population arithmetic, which is the part you can actually use.

At 1 metre by 1 metre, planting density is approximately 10,000 plants per hectare. That figure comes straight from the geometry: a hectare is 10,000 square metres and each plant occupies one square metre.

Work the other spacings the same way and you can plan any layout. At 1 metre by 0.8 metres, each plant occupies 0.8 square metres, so a hectare holds about 12,500 plants. That is arithmetic from the sourced spacing rather than a separately published figure, and it is exactly the calculation you should be able to do for your own layout.

Why does population matter so much? Three reasons, and they pull against each other.

More plants per hectare means faster canopy closure, and canopy closure at roughly 20 to 24 weeks is when weeds stop being the emergency. Anything that closes the canopy sooner shortens the window in which weeds face no competition for light.

More plants per hectare also means more competition among your own plants for water, light and nutrients, and more stakes required. At 12,500 plants per hectare you must cut and handle 25 percent more planting material than at 10,000, and Module 4 showed exactly how scarce that material is.

And more plants per hectare means less room to walk, weed and eventually harvest. A field you cannot move through comfortably is a field that gets weeded late.

That is why the branching habit of the variety belongs in the spacing decision. Module 2 gave mature plant height as typically 1 to 5 metres, an enormous range. A tall, heavily branching variety at close spacing will close the canopy quickly and then crowd itself and block your access. A compact, upright variety tolerates closer spacing. Ask about branching habit when you obtain a new variety, and if nobody can tell you, start at the wider end of the band and record what happens.

For intercropped cassava the spacing is deliberately wider, and the reported figures reflect that. Up to 200 centimetres between rows or ridges is cited where cassava is intercropped with legumes or cereals, and another source gives 1 to 4 metres depending on the branching habit of both the cassava and the companion crop.

Read that second figure carefully, because it names both crops. Spacing in an intercrop is not a cassava decision with a companion crop added. It is a decision about two plant populations sharing one piece of ground, and both branching habits set it.

The practical method on planting day is simple and worth the twenty minutes it takes. Cut a measuring stick to your chosen within-row spacing and another to your row spacing. Do not pace it out. Pacing drifts, and by the far end of a long field your rows will not be where you think, which makes mechanical or careful manual weeding harder for the whole cycle. Use a line or string for the first row and set every other row off it.

Then count. Count the plants you actually planted and compare with the population your spacing predicted. If you planned 10,000 per hectare and planted 7,000, either your spacing drifted or your stake supply ran short, and both are things to know before you interpret this season's yield.

Cassava is a natural intercrop candidate and the reason is exactly the same feature that makes it vulnerable to weeds. Its initial canopy development is slow, with full ground shading only by roughly 20 to 24 weeks. For those first months there is sunlight reaching bare ground between your rows, and something is going to use it. The intercropping question is whether that something is a crop you chose or a weed you did not.

The reported companion crops are maize, cowpea, groundnut and okra, and what they have in common is the thing that matters: a maturity cycle of 2 to 5 months.

That number is the whole principle in one figure. A companion crop maturing in 2 to 5 months is harvested and off the land well before cassava's canopy closes at 20 to 24 weeks, and before cassava's own bulking period peaks. So it does not compete for light or nutrients as heavily as a longer-duration companion would.

Hold the timeline in your head, because the argument depends on it. Cassava bulking begins around day 45 to 60 after planting. The critical weed period runs through the first 10 to 16 weeks. Canopy closure comes at 20 to 24 weeks. A companion crop maturing at 2 to 5 months, meaning roughly 8 to 20 weeks, is finishing and leaving as cassava moves into its heaviest demand.

Now the rule that follows, and it is the one this lesson exists for. Anything that stays in the ground competing with cassava through and beyond canopy closure is not an intercrop. It is a second crop being paid for out of your root yield, and the payment is invisible because you never see the cassava you did not grow.

So the questions to ask about any proposed companion crop are these.

1. How many months until it is harvested and off the land? If the answer is beyond about five months, you are into competition through cassava's bulking period.
2. How tall does it grow and how much does it shade? A companion crop that overtops young cassava is taking the light the cassava needs during the very weeks when it is establishing and beginning to bulk.
3. What does it take from the soil? Module 6 covers cassava's own heavy potassium removal. A companion crop that is also a heavy feeder on the same nutrient compounds the problem on land that may already be tired.
4. Does it share pests or diseases with cassava, or host the whitefly vector? Ask your extension office about local conditions before committing.
5. Can you still get in to weed? A dense intercrop that blocks access during cassava's critical 10 to 16 weeks defeats the purpose of planting it.

Notice that a legume such as cowpea or groundnut answers question three better than a cereal does, since legumes fix their own nitrogen. That is a real advantage in this context and it is why legumes appear alongside maize in the reported list.

The cost of intercropping is spacing, and you must pay it honestly. Intercropped spacing must be widened, up to 200 centimetres between rows or ridges where cassava is intercropped with legumes or cereals, or 1 to 4 metres depending on the branching habit of both crops. Widening rows means fewer cassava plants per hectare, which means less cassava. The companion crop is not free. You are trading cassava plant population for an earlier, second harvest.

Whether that trade is good depends on why you are farming. If you need food or cash inside four months, an intercrop that delivers a groundnut or cowpea harvest at week twelve, while your cassava is still eight months from anything, is worth real money and real food security. If you are growing cassava on contract for a processor by the tonne, thinning your cassava population to fit a companion crop may cost you more than the companion is worth.

And here is the failure to avoid above all others. Do not intercrop at monocrop spacing. Squeezing a companion crop between rows set at 1 metre by 1 metre gives both crops too little, and the cassava, being the slower plant, loses. If you decide to intercrop, decide it before planting day and set the wider spacing from the start. It cannot be fixed later.

Everything in this module comes together on one day, and planting day goes wrong in predictable ways. This lesson is the assembly, and it is written to be used rather than admired.

First, the arithmetic you do the week before, not on the morning.

Calculate your stake requirement from your area and your chosen spacing. At 1 metre by 1 metre, about 10,000 plants per hectare, so a quarter hectare needs about 2,500 stakes. Add a rejection margin, because you will discard stakes below five nodes, stakes from plants showing disease, and damaged pieces. If you expect to reject one in five, divide by 0.8, so 2,500 becomes about 3,125.

Then check that requirement against what you actually have standing. Module 4 gave you the conservative figure of about eight stakes per mature healthy plant. If the numbers do not meet, you have a decision to make this week, not on planting morning: reduce the area, source clean material from an inspected supplier, or widen the spacing within the reported band. All three are legitimate. Discovering the shortfall at 8am with a hired crew standing around is not.

Second, the moisture discipline, which is what actually distinguishes a good planting day from a bad one. Module 4 established the figure: a 20 percent reduction in cutting moisture content can reduce sprouting by 50 percent. Everything below follows from that one number.

• Cut stakes as close to planting as you can manage, ideally the same day.
• Keep the stake store in shade, always, with bundles standing upright rather than lying in a heap.
• Move stakes to the field in small batches that will be planted within the hour, not in one heap dumped at the field edge at sunrise to sit in the sun until three in the afternoon.
• Never let a batch sit exposed while you go to fetch water, food or a tool.

Third, the layout. Set your gauge sticks and a line before anyone starts planting. Establish the first row with a line, then set every other row off it with the row-spacing stick. Ten minutes of setting out saves a whole cycle of crooked rows that are hard to weed.

Fourth, orientation. Brief every person planting, including anyone who joins late, that the stake has a top and a bottom and that upside down means no plant. Use the cutting convention from Module 4, bottom square and top slanted, so that the rule is visible in the wood and does not depend on memory.

Fifth, depth and angle. Agree one method before starting: vertical, slant or horizontal, with 5 to 10 centimetres below the surface and most of the stake exposed in the vertical and slant methods. Do not let three helpers use three methods across one field, because at harvest you will not be able to tell what worked.

Sixth, count as you go. Count stakes into the field in known batches, say bundles of fifty, and keep a tally. At the end of the day you will know how many you planted, which lets you turn a four-week sprout count into a real percentage.

Seventh, write it down before you sleep. On one page, record the date, the variety, the source of the planting material, the spacing used, the planting method and depth, the ridging or flat decision, whether it was intercropped and with what, and the number of stakes planted. That page is what this season's yield will be judged against, and without it you will be guessing next year.

And then set your follow-up dates immediately, while the page is open. Four weeks for the sprouting count. Week ten as the middle of the critical weed period. Week sixteen as its end. Weeks twenty to twenty-four for expected canopy closure. Module 6 turns those dates into a weeding plan.

One last thing about labour. Planting day is a peak-labour day and the critical weed period arrives ten to sixteen weeks later, which is another peak-labour period. Plan both at the same time. Farms that arrange help for planting and then find nobody available for the first weeding have spent their effort on the half of the job that does not decide the yield.