Similar names: Retention trenches, infiltration trenches
The name Fanya chini literally means “throw it downwards” in Kiswahili. It consists of trenches and earthen ridges facing downslope. This intervention aims to reduce soil erosion by breaking down long slopes into smaller sections. Thus, the speed of runoff will decrease, and water can infiltrate into the soil between the bunds. This will result in a reduction of nutrient leaching and increased water availability for crops. Fanya chini is common in areas with 300-600 mm of annual rainfall on slopes of 1-25%. It is suitable for all types of relatively permeable soils (e.g. alluvial, red, laterite, brown, and shallow and medium black soil) but does not work very well with clayey soils or vertisol soils as these are not permeable.
- As with all earth structures, maintenance is fundamental. The structures should be reinforced every year to prevent breakages. If combined with grass strips, the grass strips require trimming to keep them dense and low, preventing them from burning during the dry season.
- A small reduction in area used for agricultural purposes will be necessary for the construction of the trenches. However, this can be limited by integrating vegetative measures, such as growing grasses or trees used for fodder between the trenches.
- Controlled grazing: grazing should be well managed and controlled so as not to damage the structures.
- Hoe (Jembe) or shovel
- Pickaxe (for hard soils)
- Draft animals or excavating machinery for more efficient excavation
- Instrument to measure the slope: some examples of tools you can use include an Abney level, a line level, or a spirit level.
- To measure the contour line, here are some examples of tools that could be used: a string line level or spirit level instrument, A-frame level. You can also ask a person who is acquainted with measuring levels (such as a masonry worker) which tool they use, and you can use the same approach to measure your land.
Steps of Implementation
The excavated soil, obtained by digging trenches 50-60 cm deep and 60 cm wide, is placed on the lower side of the contour trenches, facing downslope. This is one of the most important distinguishing characteristics of Fanya chini compared to Fanya juu, where the excavated soil is relocated upslope.
The presence of the bunds ensures the formation of micro-catchments that concentrate the runoff coming from the land that is upslope of the bunds. Contour bunds work very well with tree planting interventions because they serve well as water harvesting technology. Indeed, this system is not only often used for the cultivation of annual crops such as Zea mays (corn), Eragrostis tef (teff) and Vicia faba L. (fava beans) but it can also be used for water demanding crops such as bananas, fruits and vegetables, that are usually planted where the runoff collects (e.g. immediately above or below the bunds).
A very good step-by-step on how to build Fanja chini is provided by Justdiggit; you can find instructions here and in this video.
Estimation of costs and benefits of intervention
|Implementation cost||US $8/ha|
|Maintenance cost||US $8/ha|
Fanya chini can have a great impact on yield improvement. This example in Uganda shows a 59% increase for bananas and 56% for coffee yields after the implementation of Fanya chini intervention.
Click here for an example of Fanya chini in Tanzania, where different species like pineapple trees combined with maize and vegetables were planted on a Fanya chini, resulting in a particularly positive outcome.