Intercropping Maize and Legumes in Ghana

What an intercrop does for the land and the farm

An intercrop grows two or more crops on the same plot at the same time. In Ghana the most common pairing is maize with a legume, because the two complement each other. Maize is a tall, heavy-feeding cereal that uses a lot of nitrogen. A legume such as cowpea or soya bean partly feeds itself, through bacteria in its root nodules, and it leaves some nitrogen in the soil for the crop that follows. It also covers the ground between the maize rows, which helps hold moisture and keeps down some weeds.

For the farmer, the attraction is practical. If the rains are poor, or the maize price falls, the legume still gives something to sell or to feed. If the season is good, both crops contribute. An intercrop spreads risk across two harvests, and that is valuable on a small plot where one failure can wipe out the year.

If you are weighing the costs of a crop plan against the feed needs of your birds or animals, the poultry feed calculator helps you see what a locally grown protein source is worth in the ration.

Maize with cowpea or soya: which pairing suits which zone

Cowpea is widely grown in the north and transition zones, and it is well suited to the lighter rainfall there. It matures earlier than soya and can be harvested as dry grain, green pods or fodder. Soya bean is more common in the middle belt and parts of the north where rainfall is reliable enough for it, and it is often grown for its protein and oil. Both can work in the right place, but neither suits every farm, so check what your neighbours grow and what your extension officer recommends.

Groundnut is another legume that is sometimes intercropped with maize, but it carries higher risks of aflatoxin if it is not dried and stored carefully, so this article keeps to cowpea and soya. The principles of spacing, timing and layout apply to any legume, so you can adapt them if you already grow another crop.

The pairing you choose should fit the market too. Cowpea grain has a steady local demand for food, and the haulms are useful to livestock keepers. Soya has a strong demand from feed and processing buyers, but the crop needs more care in harvesting and drying.

Row layout: keeping the maize plant count up

The most common mistake in an intercrop is to squeeze the legume in without adjusting the maize. That cuts the number of maize plants and the maize yield drops, which can erase the gain you were after. The aim is to keep the maize population close to the level a sole crop would have, and then add the legume into the spaces that are left.

A common approach is to plant the maize in single or double rows with the legume sown in the gaps between them. A typical layout puts one or two rows of legume between two maize rows, with the maize spacing kept close to what a sole maize crop uses in your area. Your extension officer can give you the exact row spacing for your variety and your soil, and it is worth marking the plot with a rope before planting so the rows stay straight.

Count the plants in a metre of row after thinning. If you have far fewer maize plants than you planned, widen the legume gap or adjust the maize spacing next time. Keep the record, because it tells you what happened in your own field rather than what a general rule predicts.

Timing the legume so it does not shade the maize

Timing decides whether the legume helps or hurts the maize. A legume sown too early and allowed to grow fast can shade and compete with young maize, especially if it is planted in the same row. A legume sown too late gives little return and may not fill its pods before the rains end. The usual approach is to sow the maize first or on the same day, and sow the legume within a week or two of the maize, so both crops start together without the legume overwhelming the maize.

Soya usually goes in at the same time as maize, because it needs a good start to cover the ground. Cowpea can be sown with the maize or a little after it, depending on the variety. Early-maturing cowpea varieties are sometimes sown later so the maize has a head start, and this is a judgement that depends on the rainfall and the variety.

Sow into moist soil, and place the seed at a shallow depth. Planting into dry ground leads to patchy stands, and a patchy stand makes the whole intercrop harder to manage. A light rain after sowing makes a large difference to germination.

Seed, variety and inoculant for soya

Choose a maize variety that suits the planting window and the growing season in your zone. Many farmers in intercrops prefer early or extra-early maize, because it finishes sooner and leaves the legume less time in competition. Ask the extension office for the varieties they recommend, and buy certified seed from a reliable source rather than saving seed from a poor crop.

Soya bean benefits from inoculation with the right rhizobium strain before sowing, especially on land where soya has not been grown before. Inoculant is a powder or peat-based product that is mixed with the seed just before planting. Keep it cool and out of the sun, check the date on the packet, and do not mix it with fertiliser or chemical seed dressings, which can kill the bacteria. Use the inoculant on the day of sowing.

Cowpea usually nodulates well without inoculation on land where it has been grown before, but a new field may still respond to inoculant. Choose a cowpea variety that matches your purpose, whether grain, green pods, fodder or a mix, because that choice decides how you harvest and how you use the crop.

Fertiliser: what the legume does and does not replace

A legume does not fully replace the nitrogen that maize needs. It can add a useful amount to the soil, but a maize crop that yields well will still draw heavily on the soil's nitrogen. Plan a fertiliser programme for the maize as you would for a sole crop, and treat the legume's contribution as a benefit, not a substitute. Overdoing nitrogen fertiliser on an intercrop can make the legume grow too much leaf and less seed, which is the reverse of what you want.

Phosphorus is often the nutrient that limits legumes on poor soils, and it helps the nodules to form and work well. A soil test, if you can get one, tells you what the plot needs. Where a test is not possible, ask your extension officer what is usually recommended for your zone, and apply it in bands near the row at planting.

Manure and compost help both crops, especially on tired soils. Work them into the soil before planting, and avoid putting fresh manure in direct contact with the seed.

Weeds, pests and the traps that catch intercrops

Weeds are the first challenge. Maize and legume both need a clean start, and the first two to three weeks are the most important for weeding. Weed by hand or with a hoe, keeping the hoe well clear of the legume roots. A second weeding a few weeks later usually keeps the field under control until the canopy closes.

Pests can move between the two crops, so watch both. Maize stem borers can damage the maize, and pod borers and aphids can attack the legume. Scout the plot every week, look at the underside of leaves and the inside of stems, and check the pods for holes. Use crop protection products only if they are approved for the crop concerned and used exactly as labelled, including the waiting period before harvest or feeding. If you are unsure which product to use, the extension office or a registered agro-dealer can advise you.

A common trap is to treat the intercrop as if it were one crop. A spray that suits the maize may not suit the legume, and a timing that suits one crop may leave the other exposed. Plan pest control for each crop separately and keep notes.

Harvesting the legume and the maize without mixing them

The two crops rarely mature at the same time, so the harvest needs a plan. Cowpea typically matures sooner than maize and soya, and its pods can be picked in stages as they dry. Maize is harvested when the husks are dry and the grain is hard. Soya is harvested when the leaves have dropped and the pods are brown and rattle. Harvesting the legume first leaves the maize standing longer, and that can be an advantage if the maize needs more time to dry in the field.

Keep the harvests separate. Use different bags, containers and drying spots for each crop, and label them. Mixing a legume into a maize batch makes the batch harder to dry evenly and harder to sell at a fair price. A clean, labelled harvest also helps when you come to record yields.

Check the moisture of the grain before storage. Both crops need to be dried properly, and damp legume seed can spoil just as easily as maize. The principles in the sections on drying and storage apply to both.

Haulms for feed: the second return from the legume

The haulms, or stems and leaves, of cowpea and soya are valuable feed. Cowpea haulm in particular is well regarded by goat, sheep and rabbit keepers. Cut the haulm after the pods are picked, or when the crop is dry in the field, and wilt or dry it in shade. Dried haulm keeps well and can be stored for the dry season, when pasture is short and feed is expensive.

Haulms are fibrous and bulky, so they are best used as part of a mixed diet. Offer them alongside grass hay or other forage, and a mineral supplement for ruminants. Rabbits can take dried haulm as a steady part of their diet, but introduce it gradually and keep it dry, so it does not spoil in the hutch. Grasscutters will also eat dry haulm, though they waste some of it, so offer what they will finish.

Do not feed haulm that is mouldy or that comes from a field treated with a product that has not cleared its waiting period. Look at the material before you feed it, and throw out anything that smells musty or looks damp inside the bundle.

Judging whether the intercrop pays on your own plot

The usual way to judge an intercrop is the land equivalent ratio, which compares the land needed to grow each crop separately with the land needed to grow them together. A ratio above one means the intercrop uses the land more efficiently than separate crops would. Researchers often report ratios above one for well-managed maize and legume intercrops, but the number on your plot is what counts, and it depends on the variety, the weather and how well you manage the field.

To test it yourself, mark out a sole maize strip and a sole legume strip beside the intercrop, with the same planting date and management. Weigh the harvest from each part, and compare the total output against the intercrop. Do this for at least one season before you change the whole farm. A single good season can be misleading, and a single poor one can hide the benefit.

Value the outputs in the same units you care about, whether that is cedis, feed value or both. A legume that feeds your goats or rabbits may be worth more to you than its market price suggests, because it cuts the cost of purchased feed. The poultry calculators help you weigh that saving against the cost of seed and labour.

What the grain from each crop gives your poultry

Maize is the energy base of most poultry rations in Ghana, but it is low in protein. Cowpea and soya fill the protein gap, and they do it in different ways. Raw soya and raw cowpea both contain compounds that reduce the bird's ability to digest protein, so they must be heat-treated before they go into feed. Cook or roast them thoroughly, cool them, and then grind them into the mash. Never feed raw legume seed to birds. If you keep a particular breed and want to match its feed to its purpose, the breeds page is a good place to start.

The table below compares the rough protein range of each grain, and the main limit to watch. The figures are typical ranges and will vary with the variety, the soil and the year, so use them as a guide and check the analysis of your own batch.

A nutritionist can tell you how much of each to use in your mash. Home-grown protein can cut purchased feed costs, but only when it is handled and balanced properly. The broiler profit calculator and the layer egg profit calculator both show how feed cost changes the margin for each type of bird.

Planning the season and keeping records that help

Plan the intercrop before the rains start. Decide the maize variety, the legume and its purpose, the row layout, the fertiliser programme and the harvest sequence. Write it down, and buy the seed and inputs on time. Late purchases are one of the most common reasons an intercrop goes wrong, because the seed goes in after the best planting window has passed.

Keep records through the season. Note the sowing dates, the plant counts, the weeding dates, any pest problems, the weather, and the harvest weights of each crop. Those records are the only reliable way to see whether the intercrop worked on your land, and they will make next year's plan far more accurate.

If you are building a farm around home-grown feed, the guide to starting poultry farming in Ghana and the poultry farming overview explain how crops, feed and birds fit together. For the chicks themselves, the day-old chicks prices page lists the starting prices for each type, confirmed per order.

Questions farmers ask