Crop Rotation for Healthier Ghana Soils

Why the same field stops giving

A farmer asks the same question every season. The maize came up well in the first year on the new plot, then in the second year it yellowed in patches, and in the third the cobs were short and the leaves had holes in them before the tassels came out. He blames the seed, then the rain, then the fertiliser dealer. The honest answer is usually that he has planted the same crop in the same place three seasons running.

Continuous cropping is one of the quickest ways to make a field poorer. The crop takes the same nutrients out of the same layer of soil every year. The pests and diseases that feed on that crop build up in the residue and in the soil, and the weeds that like that crop's growing conditions get a head start each time. None of this is dramatic on its own. Put together over three or four seasons, it is the reason yields fall.

We are a day-old chicks hatchery, and crop rotation is not something we sell or supply. We cover it because many farmers who buy chicks from us also keep a food plot, a few acres of maize or a vegetable bed close to the house. Getting the rotation right on those plots saves money on seed and fertiliser, and it keeps the land productive for the birds' feed and the family's food.

What rotation does, in plain terms

Rotation does four jobs at once, and it is worth knowing which job matters most on your land before you plan.

• It breaks pest and disease cycles. Many soil pests and pathogens need a particular crop to survive. When that crop is missing for a season or two, their numbers fall. Nematodes, some soil fungi and bacterial wilt are the usual examples.
• It spreads the feeding load. Different crops take different amounts of nitrogen, phosphorus and potassium and draw from different depths. A field that rotates between a deep-rooting crop and a shallow one uses more of the soil profile.
• It brings in nitrogen. Legumes such as cowpea, groundnut and soya carry bacteria in their root nodules that take nitrogen from the air. Some of that nitrogen stays in the soil after the crop is harvested.
• It upsets the weeds. A weed that thrives in maize struggles in cowpea, and the reverse is also true. Changing the crop every season makes it harder for any one weed to settle in.

Rotation will not fix a field with poor drainage, a drop in organic matter or an acid soil that needs lime. Those problems need their own treatment. It works best as one part of a plan that also includes a soil test and a steady supply of organic material.

The crop groups and what they do to the soil

Rotation is easiest to plan when you think in groups rather than individual crops. Crops in the same family share pests and diseases, so they belong in the same group for planning purposes. The table below groups the crops most Ghanaian farmers grow and gives the job each group does in the rotation.

Read the table as a sequence rather than a list. A good plan puts a legume between two heavy feeders, and keeps the nightshades out of any bed where they have grown in the last two or three seasons.

A three-year cycle for the forest and coastal zones

The cycle below is one example for a plot in the forest or transition zone that gets two rainy seasons. Adjust it to your own soil test, your water supply and the markets you sell into. It is a starting point for the conversation with your agric extension officer, not a rule that must be followed to the letter.

The logic is simple. The maize in year one takes a lot of nitrogen, and the cowpea that follows gives some back. Groundnut or soya in year two adds more. The nightshades in year three go onto ground that has not held tomato or pepper for at least two seasons. Keep a note of what went where, because the next cycle depends on it.

Rotation in the northern savannah

In the north the rains come once a year, and the rotation has to fit a single season of planting. Many farmers there grow maize, sorghum, millet, groundnut and soya, with cowpea and yam on the better ground. The choice of crop is often limited by soil depth, by how far the water has to be carried and by what the local market will take.

A common approach is to alternate a cereal with a legume each year, and to keep groundnut and cowpea on the most fertile patches close to the compound. Where the land is sandy and the rains fall in a short, heavy burst, groundnut and cowpea hold up better than a maize crop that runs short of water in the middle of the season. Ask the agric extension officer which varieties suit your district, because the maturity period of a variety decides whether it fits the rains.

Plant the legume early enough to finish before the rains stop. A cowpea that is cut short by a dry spell leaves fewer haulms behind and less nitrogen in the soil, which defeats the purpose of putting it in the rotation.

Keeping the nightshades apart

Tomato, pepper and garden egg share the same weak points. They are attacked by bacterial wilt, which lives in the soil and can persist for years, and by root-knot nematodes, which swell the roots and stop the plant taking up water. Once one of these diseases is in a bed, it does not leave on its own. The only reliable way to deal with it is to stop growing these crops on that ground for a long time.

In practice that means keeping nightshades out of any bed where they grew in the last two or three seasons, and longer if you have seen wilt. Write the bed number on a stake, so you remember what was there. Do not use the same bed as a nursery for seedlings and then plant the field with the same family in the same place. Buy certified seed or seedlings when you can, and remove any plant that wilts suddenly and dies, along with the soil immediately around its roots.

Sunshine and organic matter help, but they do not replace rotation. Our notes on growing tomato in Ghana cover the nursery and the field stages, and they flag the points where wilt usually starts.

Striga and the witchweed problem

Striga, the purple witchweed, is one of the most stubborn problems in the north and in parts of the middle belt. It attaches to the roots of maize, sorghum and millet, and it can shed thousands of tiny seeds that stay in the soil for years. A field with a heavy seedbank can lose most of its cereal crop even when the rains are good.

Rotation helps by stopping the cycle. Cowpea and groundnut are not hosts for the Striga that attacks maize and sorghum, so the seedbank does not grow in those seasons, and some seed in the soil dies off while it waits. Some cowpea varieties can host a different Striga species, so ask before you rely on them. Choose cereal varieties that are tolerant or resistant, where the extension service has them. Pull Striga plants by hand before they flower, and do not let them set seed on the edges of the field, because the margins are where the seedbank grows fastest.

Because the dynamics are complex and local, speak to your agric extension officer before you rely on any single measure. Check the current recommendations from MoFA and the research institutes, since the advice on tolerant varieties and trap crops changes as new material is released.

Fall armyworm and the maize cycle

Fall armyworm arrived in Ghana in recent years and has become a regular feature of the maize season. Its caterpillars feed inside the whorl and on the cob, and a field planted to maize after maize gives the pest a steady food supply from one season to the next. A rotation that breaks the maize run does not stop the moths arriving from elsewhere, but it does reduce the number of generations that breed on your plot.

Putting a legume between two maize crops is one of the easier breaks to arrange. The larvae that hatch from moths laid on last season's maize find no maize waiting for them, so the numbers on the plot fall. Where a farmer must plant maize in consecutive seasons, scouting becomes the most important job. Check the whorls every few days from the second week after emergence, and follow your agric extension officer's advice on control, which should include the current recommendations for pesticide use and safe handling.

A cleaner field also helps. Remove the stalks of the last crop from the edges, and do not leave a heap of maize trash next to the new planting.

Legumes, nitrogen and what they leave behind

The nitrogen a legume leaves in the soil depends on several things, and none of them is guaranteed. The crop has to nodulate, which means the right bacteria must be present in the soil and the plant must be healthy enough to form nodules. A waterlogged or very acid patch often gives poor nodulation. The variety matters too, because some grow a large canopy and others put most of their energy into seed.

Seed inoculants with the right rhizobium strain can help on fields that have not grown the legume before, but check the product date and the storage conditions, because a dead inoculant does nothing. Plant on a fresh field with good drainage where possible. When you harvest, leave the haulms on the ground or chop them into the soil, rather than burning them. Those haulms add organic matter, and they are useful as mulch on the next crop (see our piece on mulching to hold soil moisture).

If the legume leaves are needed for feed, that is a fair use too. A farmer who cuts cowpea haulms for feed and returns the stems and roots to the soil has still gained most of the benefit. The balance is for you to judge on your own land.

Rotation with manure and birds

On a mixed farm, rotation and manure go together. Poultry litter, goat or sheep manure and compost add organic matter and nutrients, and they are most useful when they go onto the field that needs them in the season before a heavy feeder goes in. Put a fresh load of raw litter on a bed of tomatoes and the plants can burn. Compost it first, then spread it according to what the next crop needs.

Birds can also work the land in a planned way. A free-range flock grazing a paddock for a season leaves droppings and scratches the surface, which feeds the ground. The principle is explained in our guide to paddock rotation for free-range birds. Keep the birds off a seedbed until the crop is established, and keep them off a legume you want to harvest for seed.

For composting litter, our guide to composting poultry litter in Ghana sets out the heap, the turning and the time it takes. Once the compost is ready, spread it on the field that is coming up for the nightshades or the maize, depending on the plan.

A checklist for next season

1. Draw a simple map of the farm and number each plot, and keep the map in a folder or a notebook.
2. Write down what was grown on each plot in each season, including the variety and the planting date.
3. Take a soil test before you plan the next cycle, so you know whether the legume is needed or whether lime or organic matter comes first.
4. Keep nightshades out of any plot where tomato, pepper or garden egg grew in the last two or three seasons.
5. Choose a legume for the plot that followed a heavy feeder, and plant it early enough to finish before the rains stop.
6. Compost manure and litter before spreading it on the fields that need it most.
7. Scout the maize every few days from the second week after emergence, and log any pest you find.
8. Review the plan at the end of the season and change what did not work.

Planning rotation on land you do not own

A lot of Ghanaian farmers farm land they lease, borrow or share with family, and a rotation needs a field for longer than one season. If your tenure is short, the benefit of a legume in year two may go to the next person who farms the plot. In that case, put the legume on a plot you can reliably return to, and keep the nightshades on the ground you know best.

Ask the landowner or the customary authority what the terms are before you plan a long cycle. Land arrangements differ from one district to another, and the terms for leasing or sharing a plot are a matter for the parties involved and the local rules. Check the current terms with the district assembly where you are unsure, rather than relying on the practice of a neighbour.

When you are not sure how long you will keep a plot, it can still pay to rotate. A single legume season on a tired field is cheap, and the effect on the next crop is often clear within a season.

Where rotation fits in a mixed farm plan

Rotation is one of the quiet decisions in a mixed farm. It affects how much fertiliser you buy, how often you spray, how much labour goes into weeding and what you feed the birds. The farmers who get the most from it tend to keep notes and review them, rather than switching plans every season.

If you are adding poultry to a holding that already grows crops, the flock and the field can support each other. Litter feeds the beds, the beds grow feed and fodder, and the surplus from both goes to market. Our notes on poultry feed formulation and integrating poultry with crops and fish show how the pieces connect.

To start with birds, our day-old chicks range covers the main meat and layer lines. Ross 308 and Cobb 500 begin from GH₵20 per bird, and the current starting prices are on our prices page. You can see the breeds on the breeds page, order from the order form, or WhatsApp us on +233 24 915 1503. Email is support@halaalfarms.com, and our partner page explains how we work with farmers who want to grow the business in stages.

Questions farmers ask