Improved Fallows



Similar names: mixed improved fallows, mixed intercropping, shade trees, relay intercropping

Cultivating mixed improved fallows is a technique that aims at keeping yields high while maintaining soil fertility and moisture. This is achieved by growing two or more species in succession, sown at different times on the same land area, which positively influence each other while providing nutrients to replenish the soil. The soil should never be left exposed, but always covered by crops and mulch. Traditionally, farmers used to leave a part of their land to “rest” (the fallow) for one year or more after a period of intense cultivation. This allowed the soil to be covered by natural vegetation which restored nutrients, organic matter, and soil microbial activity necessary to make the soil fertile. However, with increasing demand for resources, this has become a practice which is rarely used.

To keep or restore soil fertility, some farmers have come up with the solution of planting fallow plants (which can be a tree, a shrub or an herbaceous cover crop – often a leguminous species), during the fallow phase. Fallow plants are used to: provide fodder, break cycles of pests (as some species are natural pest-repellents), attract honeybees, keep weeds away, shade crops, increase soil activity, and increase biodiversity.

Mixed improved fallows can perform even better: here, two or more fallow species are combined with one traditional crop. One of the two fallow species usually grows very tall and provides shade, while the other is a “nitrogen fixing” plant which restores the nutrients in the soil.

  • Improve soil health
  • Increase vegetation
  • Increase crop yields

  • It is a technique that requires good management and knowledge of what to plant and when.
  • This intervention requires seeds.
  • It might require some adaptation time (to figure out which plant combinations work best).
  • Pest management: it is important to understand which pests affect which species so as to not place those species in a close rotational succession.
  • Water management: if not planned correctly, fallow species can cause competition for water with the fast-growing traditional crop.
  • Although some fallow species are very good at keeping away pests, they can sometimes attract pests that affect particular types of crops (such as root-knot nematodes in the Sesbania sesban and beans plants), therefore, it is recommended not to plant beans in the first season after these fallows.

Fallow plants are usually planted halfway through the dry season, especially when using species with deep roots. They should be left to grow in the soil for a prolonged period of time (ideally from 6 to 12 months depending on the species used). A traditional fast-growing crop is then planted during the wet season in between the fallow species in order to provide the traditional crop with partial shade and to keep the soil fresh. Once too big, fallow plants are trimmed or cut and used as mulch or green manure to replenish the soil. Sometimes, the fallow species produce high amounts of biomass which can be used as firewood (where trees are used) and fodder, or sold on the market (where beans and fruit trees have been planted). Trees used in an improved fallow intervention can be planted via direct seeding or by transplanting seedlings. More information about the establishment of an improved fallow can be found here.

Characteristics of a fallow plant:

  • It grows fast and suppresses weeds with the shade
  • Its biomass is high, of good quality and it decomposes fast, guaranteeing a fertile soil for the crop
  • It has deep roots so as to take up water and nutrients deep in the soil
  • It is easy to establish and manage
  • It is not invasive
  • It easily produces seeds that can be used in the next season
  • It is adapted well, resists to pests and diseases of the area


If fallow species are not an option, it is still important to highlight the benefits of a rotational crop system instead of planting the same crop at the same place each year (monoculture). Alternating crops such as maize or wheat with leguminous species such as beans (which are nitrogen fixing species with long roots) will benefit the soil in terms of water retention and nutrients.

This intervention contributes to:

Estimation of costs & benefits of intervention

Establishment cost Maize seeds: US $4/ha, Tree seeds:  US $8/ha. Total cost US $12/ha (without labor cost)
Labor time Maize: 136.4 workdays/ha, Tree sowing: 17.5 workdays/ha. Total labor /ha: 153.9
Maintenance time Cutting trees 17.5 workdays/ha
Benefits Maize yield: US $82/ha, Fuelwood US $10/ha (after the 3rd season)
Cultivated products Maize, Sesbania seban,
Price per product Maize price = US $0.14/kg (US $1 = 30 Kenya Shilling).

Source: based on a case study in Western Kenya, 1991

In Kenya, mixed fallows of Sesbania sesban combined with, Macroptilium atropurpureum, Crotalaria grahamiana or groundnut (peanut), resulted in a maize grain yield increase of 1-2 t/ha after a 6-9 month period of fallow, and 2-5 t/ha after a 12-15 month period of fallow. Click here if you want to know more about it.

Farmers in Kenya grow sunflowers as fallow plants to attract aggressive African bees or grow chili peppers so that they keep away elephants which keep raiding their crops. Here you can read more about this interesting project.

  • If you aim at using tree species in your improved fallows intervention, here is a good step-by-step guide to plant nitrogen-fixing trees.
  • For better indication on species and sowing times (specifically for Kenya), and income see this article.
  • Visit this database as an indication for which species to use in improved fallows in tropical landscapes, and click here to have a description and characteristics of each suitable species and their English common name.