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Home  > Question of the Week

Question of the Week

Permalink Do the allelopathic characteristics of sweet potatoes influence subsequent crops? I want to plant carrots following my sweet potatoes and I’m concerned about decreased yield and increased pest pressure.

Answer: Your concerns for planting carrots after sweet potatoes are valid. Allelopathy is a chemical process that many plant species use to prevent other types of plants from growing too close. These chemicals are called allelochemicals. Depending on the plant, allelopathic substances can be released from a plant's flowers, leaves, leaf debris and leaf mulch, stems, bark, roots, or soil surrounding the roots. Sweet potatoes release these defensive chemicals into the soil through their roots in a process called exudation. Those chemicals are absorbed by the roots of other nearby plants, which are damaged. While some of the chemicals biodegrade over time, others can persist in the soil.

Research shows two tuber crops should not be planted in the same rotation because of disease and pest purposes. Planning a crop rotation scheme that allows a few years between potato crops on the same land is recommended. For organic production, a lengthy rotation from four to seven years generally assures good plant and soil health. A lengthy rotation also reduces long-term reliance on expensive inputs and increases the percentage of marketable potatoes. A good rotation includes crops that are not hosts to common potato pests. A good rotation also includes green manures that add nutrients and organic matter to the soil. Additionally, planting a legume crop after a tuber crop will add nitrogen and other essential minerals to the soil.

Early research suggests that allelopaths can be used as effective herbicides for organic weed control. For example, an allelopathic crop might be beneficial in controlling weeds by planting it in rotation with other crops.

For more information, consult the ATTRA publication Potatoes: Organic Production and Marketing at



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