Why is this subject important to listeners?
Because small-scale farmers should know:
- How growing certain crops together (mixed cropping) can increase their yields.
- Which crops that can be grown together without interfering with each other’s growth and maturity, for example maize and legume crops. There is also a mutualism between maize and legumes because beans produce nitrogen and maize consumes much nitrogen.
- That some plants or crops, for example, agroforestry species, can support vine crops without interfering with their growth and maturity.
- How crop companion planting and mutualism can help make small-scale farmers food-secure by enabling them to harvest more than one crop and increase their income by diversifying their market opportunities.
- The positive impact of mixed cropping and mutualism on soil coverage and fertility. For example, when a legume cover crop is planted alongside maize, the tall maize plants protect the beans, while the beans fix nitrogen. Also, deep-rooted legumes like pigeon pea can break through hardpans, helping maize roots penetrate deeper soil.
- The kinds of agroforestry trees that help crops thrive without interfering with their growth.
What are some key facts?
- It’s important to note that farmers must carefully choose crops to be interplanted. For example, you shouldn’t intercrop two crops such as maize and sunflower, which are both “heavy feeders,”—that is, they require a lot of soil nutrients.
- Vanilla is intercropped with bananas and coffee which provide shade, and trained on Jatropha curcas in Kagera, Kilimanjaro, and Morogoro regions.
- When black pepper was intercropped with Grevillea robusta in the East Usambara Mountains of Tanzania, it yielded 3.9 times more than in a monoculture system. And where cardamom was intercropped with Grevillea and pepper, it yielded 2.3 times more than when grown as a monocrop.
- In southeast Tanzania, farmers intercrop maize with sesame to reduce the incidence of crop failure in sesame monoculture. Though intercropping reduces yields of both crops, it helps suppress weeds, improves soil fertility, and reduces the need for scarce labour.
- Cabbage aphids attack cabbages, leaving a sooty mould on the leaves and reducing yields. Intercropping cabbages with garlic or onions minimizes aphids’ ability to disperse and find cabbages because they are repelled by the scent of these crops. The pungent scents also repel diamondback moths which feed on cabbage leaves.
- In semi-arid regions, mango or pawpaw trees can shade vegetables and minimize water evaporation. To achieve maximum benefit, mango and pawpaw must be planted either due east or due west of vegetables.
- In Tanzania, farmers grow vegetables such as cabbages in the same field as bananas. This diversifies small-scale farmers’ incomes.
- Intercropping generally increases natural pollinator populations, and better pollination helps increase crop yields.
- Crop rotation helps break disease cycles, improving yields and increasing soil fertility and soil structure.
What are the big challenges of companion planting and mutualism?
- Intercropping can sometimes result in lower yields for both crops, for example, maize and sesame, since they may compete for the same levels of light, nutrients, moisture, and root space.
- Mixed cropping is more practical in small-scale farming, since managing and harvesting more than one crop in a large-scale production setting can be challenging. Mixed cropping can also be more challenging on farms that use mechanized practices.
- Farm management practices for individual crops in companion planting systems may be somewhat different.
- Farmers lack knowledge on which plants or trees are beneficial for each other in companion planting systems.
- If one crop in an intercropping or companion planting system matures and is harvested first, weeds can grow in the spaces left behind.
- In companion planting, the ability to use pesticides may be restricted because different crops may respond differently. For example, one crop may tolerate a pesticide well, while another may not.
For further information, see documents 1-20
Gender aspects of companion planting and mutualism
- Women may be more likely to favour companion planting over monoculture systems because it guarantees different types of food for their households.
- In Tanzania, women prefer planting sweet potato varieties that can be intercropped without affecting either crop’s yield.
- Due to lack of resources to obtain inputs for more than one crop, female maize farmers in southern Tanzania are less likely to intercrop than male maize farmers.
- In Tanzania, both men and women intercrop cassava with maize, cowpeas, sorghum, and groundnuts.
- Push-pull technology* is likely to be adopted by small-scale women farmers since it reduces manual labour, improves soil fertility, increases grain yields, and increases income.
For further information, see documents 8 and 9.
Predicted impact of climate change on companion planting and mutualism
- Intercropping with leguminous crops maintains or improves soil carbon, which helps reduce emissions of greenhouse gases.
- In water-stressed regions, intercropping and planting cover crops helps crops to conserve and efficiently utilize the moisture available to them.
- Sustainable intensification, * when combined with intercropping, helps small-scale farmers minimize the financial risks associated with monoculture systems in which one crop can fail due to climate change.
For further information, see documents 8 and 18.
Key information about companion planting and mutualism
When planted together, some combinations of crops benefit each other as they grow and mature, for example, by minimizing pest infestations.
Maize mutualism with other crops
In East Africa, maize is traditionally intercropped with crops such as bean, cowpea, soybean, groundnuts, and sesame. Because legumes require less water than maize, intercropping maize with legumes such as these reduces the risk that farmers face if maize crops fail when rains are minimal. Also, these crops are compatible with maize because they have different root systems and take up nutrients from a different soil zone than maize.
The benefits of intercropping maize with other crops are as follows:
- Legumes fix atmospheric nitrogen in the soil. Soil bacteria transform this into nitrates, which growing maize requires in big quantities.
- Maize-legume intercrops help small-scale farmers to be both food-secure and economically secure since they can sell surplus yields.
- In Tanzania, sesame is considered a cash crop and is intercropped with maize, which is typically considered a food crop for small-scale farming households.
- Sesame helps suppress the root knot nematode that affects growing maize.
- Sesame improves soil tilth* and retention of soil moisture, which benefits growing maize.
- Maize and legume intercrops provide better livestock silage than if either is grown as a sole crop.
- Planting a row of soybeans between two rows of maize helps minimize striga damage.
- Cowpea is tolerant to shade and, when intercropped with maize, fixes nitrogen in the soil, boosting maize yields and suppressing weeds.
For further information, see documents 8, 11, and 18.
Vanilla, banana, legume, and coffee mutualism
Vanilla is a high-value vine crop grown in regions such as Arusha, Kilimanjaro, Kagera, and Morogoro in Tanzania. In Tanzania, a kilogram of vanilla pods sold for $27-$35 US in 2018 and a two-metre vine for $1.10. But prices vary over time. In 2020, the price was $180 per kilogram, and it is much lower in 2022. Vanilla requires shade to thrive and is intercropped with bananas, coffee, or fruit trees in agroforestry systems. Bananas and fruit trees support crawling vanilla vines. Small-scale farmers benefit in the following ways from this arrangement:
- Vanilla requires little space to grow and yield well.
- Vanilla isn’t vulnerable to pests and diseases and doesn’t need fertilizer.
- Growing vanilla with other crops maximizes farmers’ income and produces yields without the need to find more farmland for cultivation.
- In coffee plantations, potatoes and legumes such as beans can be planted as low-tier crops and be a source of food for small-scale farmers.
For further information, see document 6.
Agroforestry and spices mutualism
In Tanzania’s East Usambara Mountain region, research showed that black pepper yielded 3.9 times higher when intercropped with Grevillea robusta compared to monocultured pepper. Where cardamom was intercropped with Grevillea and pepper, it yielded 2.3 times more than when grown in monoculture. Small-scale farmers in Morogoro Region use the following trees, which, in addition to providing fruit and timber, are also useful for supporting black pepper vines:
- Silver oak
- African mahogany
For further information, see documents 17 and 19.
Mutualism in vegetables
There are vegetables and other plants that, when grown together, minimize pest attacks and provide other benefits to each other.
- Plants such as lavender, nasturtium, Mexican marigold, garlic, rosemary, and chili can be grown between vegetable rows or around the perimeter of vegetable fields to repel pests.
- Plants with tiny flowers can be planted around vegetable fields to attract friendly wasps that prey on insect pests or to attract parasitic wasps that deter pests.
- Vegetables in semi-arid regions can be grown among banana, pawpaw, and mango trees which provide suitable shade (not over-shading) and minimize water evapotranspiration *. This intercropping system ensures that small-scale farmers are food secure and diversifies their income if they sell fruits. It works particularly well for farmers with small pieces of land.
Cabbage is among Tanzania’s most important vegetable crops. It’s cultivated all year round, largely in monoculture systems. On smaller pieces of land, it’s practical to intercrop cabbage with bananas, coffee, onions, tomato, Indian mustard, or garlic. Intercropping benefits growing cabbages in the following ways:
- Onions release a scent that confuses the cabbage aphids that attack tender cabbage leaves. The scent repels the aphids, limiting their populations and ability to spread. Cabbages are planted two weeks after planting onions.
- The diamondback moths which lay eggs and feed on cabbage leaves are repelled by the scent of onions or garlic, when planted alongside cabbages.
- Indian mustard acts as a trap crop* and limits diamondback moth infestations on cabbages. When it is planted between cabbage rows, the moths feed on Indian mustard instead of cabbages.
- Radish, Chinese cabbage, and Indian mustard are ideal trap crops for flea hoppers, cabbage webworms, and mustard aphids. A row of the trap crop is planted after each 15 cabbage rows. Rows of mustard can be positioned either in the outer or middle row to prevent caterpillars from being blown by the wind onto cabbage plants. Indian mustard should be planted 12 days before cabbage seedlings are transplanted.
- Farmers can reduce thrips populations by intercropping cabbages with plants that repel them, including spider plant and coriander.
- Tomatoes grow well next to cabbages, which deter caterpillars in cabbages.
Using living plant barriers
- Planting Mexican marigold and sunflower can help contain thrips. Mexican marigold attracts thrips, which are then eaten by Orius bugs hosted by sunflower plants.
- Tomatoes act as a physical barrier to pests like the diamondback moth when intercropped with cabbages.
- Research found that cabbages intercropped with tomatoes suffer less damage to their heads in organic farming systems than those which are not intercropped.
For further information, see documents 1, 2, 7, 12, 14, 15, and 16.
Sweet potato intercropping
In areas where land is scarce, sweet potatoes are intercropped with maize, beans, pigeon peas, and sugarcane. Sweet potato vines are planted on ridges while the other crops are planted in rows. Here are some benefits of sweet potato intercropping:
- As a cover crop, sweet potatoes inhibit weeds that can affect maize.
- Sweet potatoes benefit from any residual fertilizer or manure applied on a preceding maize crop.
- Sweet potato strip intercropping* has been found to lessen weevil infestation in maize.
- Pigeon peas add nitrogen to the soil, which helps increase sweet potato yields.
- When pruned or after dropping their leaves, leguminous trees and shrubs provide nitrogen-rich green manures that increase sweet potato yields in agroforestry farming systems.
- Sweet potatoes can be intercropped with maize. The sweet potatoes cover the soil, shielding it from erosion and suppressing weeds. Maize is planted in the middle of the field, while sweet potatoes are planted on the perimeters.
For further information, see documents 4, 13, and 20.
Intercropping and biodiversity
Intercropping can help increase the number of natural pollinators.
- Mustard plants have abundant nectar and pollen, so bees love them.
- Planting leguminous trees around the farm can attract natural pollinators like bees.
- Soybean, which attracts bees, can be strip intercropped with maize.
- Sunn hemp is a legume cover crop that attracts bees and can also be intercropped with maize. It adds nitrogen to the soil.
- Research found that intercropping wheat and mustard increases honeybee populations and crop yields.
- Intercropping onions with wheat or mustard minimizes aphid infestations on both crops. Mustard flowers also attract honeybees.
For further information, see document 9.
Push-pull farming systems
The push-pull system is being gradually adopted by small-scale farmers in East Africa to help address soil infertility and pest problems, suppress striga, and provide livestock feed. Here is how it works:
- Maize, millet, or sorghum are planted as the main crop and the legume greenleaf desmodium (Desmodium intortum) between the rows as an intercrop.
- On the farm perimeter, Napier grass is planted. The Napier grass attracts stemborers, which lay eggs on the grass instead of maize.
- Desmodium repels stemborers from maize while fixing nitrogen in the soil, which improves soil fertility.
- Chemicals secreted by desmodium roots inhibit the growth of striga seeds in the soil, reducing their impact on growing maize.
For further information, see document 5.
Companion crops for support and protection
Crops that are easily knocked down by strong winds can benefit by being supported by other crops, trees, or shrubs.
- Fruits like passion can be supported on Grevillea robusta.
- Grevillea robusta trees can be planted on farm edges to act as a windbreak, protecting crops like maize from being uprooted by strong winds.
- When intercropped with legumes like cowpea, peanut, mung bean, and black or red beans, cassava plants support them. After harvest, cassava and legumes provide farmers with protein and carbohydrates. These intercrops help suppress weeds and improve soil fertility, which benefits both cassava and the legumes.
- Legumes such as groundnuts can be intercropped with cassava and bananas. Cassava also acts as a windbreak when intercropped with bananas and maize.
For further information, see documents 3 and 4.
- Banana and plantain can be planted in a field with coconut trees, with shorter crops like cassava, and with shallow-rooted plants like ginger and turmeric that are unaffected by shading.
- Livestock fodder plants can be planted as low-level plants. When banana trees are spaced widely, legumes such as beans can be planted as a low-level crop.
- In the small spaces common in urban areas, farmers can build multi-story gardens in which each tier contains a different variety of vegetable—for example, spinach, collard greens (sukuma wiki), and capsicum. Vegetables mature quickly and can provide a household with needed vitamins and save them the costs of buying vegetables.
For further information, see documents 6 and 14.
- Evapotranspiration: Loss of water from the soil both by evaporation and by transpiration from the plants growing in it.
- Push-pull technology: An integrated pest management technique that controls stemborers and striga weeds and improves soil fertility in cereal farming systems.
- Soil tilth: The condition of the soil and its suitability for planting and growing crops. A soil with good tilth is loose with fine and easy-to-crumble particles, granular, and not compacted. It has good water-holding capacity and allows water to easily percolate into the soil.
- Strip intercropping: Growing two or more crops in narrow strips to maximize productivity. Each strip can be managed independently. The crops in these narrow strips can positively influence the microclimate and yields of bordering crops.
- Sustainable intensification: A system in which agricultural yields are increased without adverse environmental impact and without converting non-agricultural land.
- Trap crop: Crops planted on field edges or intercropped with the main crop to lure insect pests to feed on them instead of the main crop. Trap crops reduce pesticide use.
Where can I find other resources on this topic?
- Agricultural Research Council-Vegetable and Ornamental Plant Institute, 2013. Production Guideline for Summer Vegetables. https://www.arc.agric.za/arc-vopi/Leaflets%20Library/Production%20Guideline%20for%20Summer%20Vegetables.pdf (16.4 MB).
- Baidoo, P. K., Mochiah, M. B., and Apusiga, K., 2012. Onion as a Pest Control Intercrop in Organic Cabbage (Brassica oleracea) Production System in Ghana. https://pdfs.semanticscholar.org/7ec9/8b9ef0ec71d4bf86320c1ef98af67dc609c0.pdf (168 KB).
- Dung, T. T. and Sam, N. T., undated. Farmer Participatory Research (FPR) Trials On Cassava Intercropping Systems In Vietnam. https://betuco.be/manioc/Cassava%20-20Intercropping%20Systems%20Vietnam.pdf (170 KB).
- Hauser, S., et al, 2014. Cassava system cropping guide. https://www.iita.org/wp-content/uploads/2016/06/Cassava_system_cropping_guide.pdf (695 KB).
- ICIPE, 2019. From Lab to Land: Women in push–pull agriculture. https://www.push-pull.net/women-push-pull-web.pdf (7.05 MB).
- International Trade Centre, 2014. Tanzania Spices Sub-Sector Strategy. https://www.intracen.org/uploadedFiles/Tanzania-Spices%20Roadmap%20_final.pdf (3.51 MB).
- Kiplagat, G. et al, 2019. Cabbage Production. https://www.jica.go.jp/project/english/kenya/015/materials/c8h0vm0000f7o8cj-att/materials_21.pdf (2.83 MB).
- Kiwia, A., et al, 2019. Sustainable Intensification with Cereal-Legume Intercropping in Eastern and Southern Africa. https://pdfs.semanticscholar.org/58a1/41e960fcc16f1c1a92beb8bd4216f66fac6b.pdf (1.63 MB).
- Mayes, D., 2011. Pollinators in Africa: Understanding is the First Step to Protecting. https://www.sanbi.org/wp-content/uploads/2018/03/pollinafricabookletweb.pdf (5.26 MB).
- Mitchell, D., Varangis, P., and Goff, V., 2016. The Effects of Gender on Maize Production and Marketing in Southern Tanzania. https://land-links.org/wp-content/uploads/2018/03/USAID_Land_Tenure_SERA_World_Bank_Policy_Brief.pdf (2.56 MB).
- Mkamilo, G. S., 2004. Maize-sesame intercropping in Southeast Tanzania: Farmers’ practices and perceptions, and intercrop performance. https://edepot.wur.nl/116594 (3.48 MB).
- Moir, K., Vandenbosch, T., and Scull-Carvalho, S., 2007. Growing Trees and Gardens for Life: practical tips for healthy tree nurseries and home gardens. http://apps.worldagroforestry.org/downloads/Publications/PDFS/b15299.pdf (2.86 MB).
- Mudege, N. N., and Grant, F. K., 2017. Formative Gender Evaluation: Technical Report on the Viable Sweetpotato Technologies in Africa – Tanzania project. https://cgspace.cgiar.org/bitstream/handle/10568/82707/CIP-Formative-Gender-Evaluation.pdf?isAllowed=y&sequence=7 (3.84 MB).
- Mulenga, M. M., Matimelo, M., and Mgomba, H., 2014. Intercrop cabbage with onion against aphids. https://www.plantwise.org/KnowledgeBank/FactsheetAdmin/Uploads/PDFs/20157800265.pdf (1.04 MB).
- Ochieng, V., et al, 2016. Cabbage Cultivation Manual. https://www.kalro.org/sites/default/files/Cabbage-Cultivation_in-Kenya.pdf (16.8 MB).
- Parker, J. E., et al, 2013. Companion Planting and Insect Pest Control. https://cdn.intechopen.com/pdfs/42925/InTech-Companion_planting_and_insect_pest_control.pdf (5.26 MB).
- Reyes, T., et al, 2009. Spice crops agroforestry systems in the East Usambara. Mountains, Tanzania: growth analysis. http://cipotato.org/site/inrm/home/publicat/2009pse3.pdf (302 KB).
- Senbayram, M. et al, 2016. Legume-based mixed intercropping systems may lower agricultural born N2O emissions. https://energsustainsoc.biomedcentral.com/track/pdf/10.1186/s13705-015-0067-3.pdf (658 KB).
- Shango, A. J., Majubwa, R. I., and Maerere, A. P., 2020. Extent of spike shedding and stem wilting of pepper (Piper nigrum L.) in Morogoro District, Tanzania. https://cabiagbio.biomedcentral.com/track/pdf/10.1186/s43170-020-00006-7.pdf (3.19 MB).
- Stathers, T., et al, 2018. Everything You Ever Wanted to Know About Sweetpotato. https://cgspace.cgiar.org/bitstream/handle/10568/98338/CIP_SP_T6_SweetpotatoProductionAndManagement_v40.pdf?sequence=10&isAllowed=y (7.61 MB).
Contributed by: James Karuga, agricultural journalist, Kenya
Reviewed by: Wayda Peter, District Crop Officer, Karatu District Council, Arusha, Tanzania.