intercropping practices

There are four main intercropping patterns: row intercropping, mixed intercropping, strip intercropping and relay intercropping.

In row intercropping, two or more crops are planted simultaneously in separate rows. How and if the plants compete for resources is dependent on the numbers of rows, the spacing and the types of cultivars, although some competition for light and nutrients can be expected.

Mixed intercropping describes a pattern in which two or more crops are grown together in no specific order. In this respect, it is expected that competition between the component crops will occur due to their close spatial proximity.

Strip ­intercropping occurs when two crops are grown in independent sections that are far enough apart to allow independent cultivation and prevent competition, but close enough to allow for complementarity.

Relay intercropping describes a crop pattern in which two types of crops at different stages of their life cycles are grown together. Typically, the second crop is planted between the flowering and harvest of the first crop. It is not uncommon for relays to be complex in nature, e.g. in the case of the popular Three Sisters method where low hill rows separated by 90-120cm are first planted with Maize, followed by pole beans planted at the base of the Maize when it is c. 15 cm, and finally a week later squash is planted around the edges of the plot and in every seventh row.

Beyond spatial constructions, there are several variations of intercropping. For example, insectary intercropping is the substitution of one or more rows of the primary crop with flowering plants for the purpose of increasing natural enemy or pollinator populations above ordinary levels and conserving them in times of low prey abundance or nectar availability.

The trap crop method describes an approach where either a cultivar more attractive to a given pest is planted alongside the main crop or the same crop is planted in two intervals so that a subsection of that crop is at the pest’s preferred maturity before the main crop reaches full maturity. The pest is then drawn to the trap crop, and the farmer can subsequently choose to either mechanically remove the pest or the trap crop to prevent further infestation.

Repellent intercropping is another approach where plant varieties that are offensive to a specific type of pest are incorporated into a growing space to deter the pest. In this approach, more rows of the repellent crop must be used than in the trap crop approach. How the repellent crop discourages the pest can be both chemical and physical in nature, or it may be a combination of both.

Trap and repellent intercropping may also be combined to create an approach known as push-pull intercropping, an approach rapidly gaining popularity in Africa. In this system, Silverleaf desmodium (Desmodium uncinatum) is intercropped with maize (Zea mays), Napier grass (Pennisetum purpureum), and Sudan grass (Sorghum and drummondii hybrid). The logic is as follows.

1. The desmodium repels (pushes) pests like the Maize Stemborer
2. The grass attracts (pulls) the stemborer moths which then lay their eggs on the grass instead of the maize. Since Sudan grass produces a gummy substance, the larvae become trapped and unable to reach maturity to reduce overall populations
3. At the same time, the desmodium encourages Witchweed (Striga hermonthica) seeds to germinate while preventing them from attaching to the maize roots
4. The Striga then dies before maturity causing the overall number of seeds in the soil to be reduced
5. Finally, the desmodium fixes nitrogen into the ground to improve overall fertility

Another variation of intercropping is companion plant intercropping where a cash crop is planted with another plant that is not harvested in order to benefit both the crop and the environment. In this approach, the companion crop is often selected for its ability to compete with weeds, although other benefits may also be sought.

Of course, it is always possible to mix and match according to the needs of your growing space!

sources:

• Bickerton, M. W. & Hamilton, C. G. (2012). Effects of Intercropping With Flowering Plants on Predation of Ostrinia nubilalis (Lepidoptera: Crambidae) Eggs by Generalist Predators in Bell Peppers. In Environmental Entomology, 41(3), pp. 612-620.
• Brion, G. (2014). Controlling Pests with Plants: The power of intercropping. 
• CALS (Cornell University of Agriculture and Life Sciences). How to Plant Three Sisters. 
• CIAT (Centro Internacional de Agricultura Tropical). (1986). Principles of Intercropping with Beans; study guide to be used as a supplement to the audio-tutorial on the same topic. Scientific content Jeremy Davis, J. B. Smithson. Production Oscar Arregocés. Cali, Columbia. CIAT. pp. 40. (Series 04EB-12.05).
• Khan, Z., Amudavi, D., Picket, J. (2008). Push-Pull Technology Transforms Small Farms in Kenya. In PAN North America Magazine, 20-21. 
• Lithourgidis, AS; Dordas, CA; Damalas, CA and Vlachostergios, DN. (2011): Annual Intercrops: An Alternative Pathway for Sustainable Agriculture [online].In Australian Journal of Crop Science.  5(4), pp. 396-410. 
• Mousavi, S., & Eskandari, H. (2011). A General Overview of Intercropping and Its Advantages in Sustainable Agriculture. In Applied Environmental Biological Sciences. 1 (11), pp. 482-486.
• Verret, V., Gardarin, A., Pelzer, E., Médiène, S., Makowski, D., Valantin-Morison, M. (2017). Can legume companion plants control weeds without decreasing crop yield? A meta-analysis. In Field Crops Research, 204, 158–168.

photo credit:

• BigHAAT.com
• sciencedirect.com