Intercropping

In the Field

Intercropping is an agricultural management practice with roots in traditional farming worldwide. Examples of intercrops range from simple soybean-corn systems, in which the plants coexist in neatly planted rows, to tropical homegardens with tens of different crop species intermingled in no row pattern whatsoever. When planning an intercrop system, a farmer must consider the different agroecological roles of plants. For example, intercropping similar crops such as broccoli and kale, which are both in the Brassicaceae family, could result in nitrogen depletion from the soil because the brassicas are heavy nitrogen feeders. It might be more beneficial to intercrop the kale with a bush bean, which can fix nitrogen and return it to the soil.

Intercropping Ecology

Intercropping can benefit pest and weed management; alter soil, water, and light dynamics; and increase farm productivity. Describing and understanding the ecological mechanisms behind these benefits is a central focus of the field of agroecology. What follows is a brief review of ecological theory relevant to intercropping.

In an intercrop, pest damage may be reduced through a variety of means such as food source interruption, natural enemies, or trap crops, to name a few. Food source interruption occurs when a pest encounters a plant that is not food. For example, an insect that specializes in cucumber foliage will flourish in a monoculture of cucumbers but may leave the system if it encounters a tomato in a cucumber-tomato intercrop. Incorporating plants that attract the natural enemies of a particular pest into an intercrop may help control pests through predation and parasitism. Trap crops are usually noncrop plants that are attractive to crop pests and draw the pests out of the productive portion of the agroecosystem.

Intercropping can reduce weeds by having mixed crops occupying open ground or through allelopathic inhibition. In an intercrop, there is often less bare ground than in a monoculture, which means there is less space for weeds to colonize. For example, in a sugarcane monoculture, weeds could easily fill in bare space between cane plants. If a ground-covering vegetable such as squash were intercropped into the system, that space would be unavailable for colonization by weeds. Allelopathic control of weeds is also possible in an intercrop when a plant with known allelopathic attributes, such as wild mustard, is planted. The chemicals released by the mustard plant through its roots and leaves can inhibit the growth of weeds in the system.

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