In the previous article we looked at the different agroforestry systems used in the humid highlands. In this issue, we consider the systems suitable for humid lowlands.

The humid lowland zone covers areas with an altitude ranging between 900 and 1 800 m above sea level and an annual rainfall of between 950 and 1 500 mm.

These areas include most parts of western Kenya, part of the Rift Valley and parts of the coastal region. The zones have diverse agroforestry practices that provide a source of livelihood for many households in the region.

Agroforestry practices in humid lowlands include the following systems:

Improved fallows

For improved fallows, Tephrosia vogelii, T. candida, Crotolaria grahamiana, Sesbania sesban and Crotolaria paulina, among others, are planted to improve soil fertility.

Land cannot be planted continuously without a break, but needs to be fallowed, or not planted, from time to time to restore soil fertility. Shrubs, that can add organic material and fix the nitrogen in the soil, can speed up the process.

Fallowing is practiced in western Kenya mainly in the Lake Victoria basin and in semi-arid areas, but the practice is not common in the rest of the country. Neither is planting shrubs quite common. Improving fallows is relevant where farms are relatively large, and where labour is more of a constraint than size of the farm.

As many individual shrubs with a relatively short life span are required, direct sowing is a simple and cheap propagation method. The denser the spacing, the more effectively the plants will suppress weeds.

Once the shrubs are established, they require little management but must be protected from livestock. Densely spaced shrubs can be thinned out for harvesting or as staking material, firewood or making masks. When land is once again cultivated, some shrubs can be left to supply propagation material for the next fallow period.

Fallowing’s main benefits are quick restoration of soil fertility and wood production. However, care must be taken to keep livestock way from the shrubs and increased labour is necessary to establish and later remove the shrubs.

Nitrogen-fixing shrubs, which are easy to propagate, and which have a short lifespan and relatively small root system, such as Sesbania spp. and Gliricidia sepium are desirable.

Crops are grown on land between the trees. (Source: https://bioone.
org/ContentImages/Journals/mred/22/4/0276-4741_2002_022_0332_
PARWUC_2.0.CO_2/graphic/i0276-4741-22-4-332-f03.jpg)

Scattered trees in croplands

Indigenous Markhamia lutea, Grevillea robusta, and Mangifera indica are planted for shade, timber and poles, fuelwood, fruits and nutritional diversity, as well as the improvement of soil fertility.

Scattered trees are found in fields in most farming areas where they were left when the land was cleared for agriculture. Also, seeds that may have been naturally dispersed and germinated, as well as farmers deliberately protecting the seedlings, may have caused the trees to grow there. Usually in such cases, the spatial arrangement is random, but sometimes trees are sown or planted on purpose, and then they are usually in lines. Lined-up trees are easier to work with in areas where farming is mechanised.

Most often, it is feasible to have trees in cropland, but it is especially relevant in areas with shade-tolerant crops like coffee or beans. In irrigation schemes, the possibilities are limited.

The benefits of these trees regarding soil structure and fertility are mostly more noticeable where little or no inorganic fertiliser is used.

There are many ways to propagate trees, and the chosen method will depend on the species used. Protection of wildings where they naturally germinated is a good option and must be considered before recommending nursery production of seedlings. When trees are to be grown in lines, direct sowing may be feasible for then you know where they will germinate.

In areas with high potential, where a crop like maize needs a lot of light, a population of up to 100 trees per hectare (10m x 10m) will be appropriate. Instead of square spacing, trees can be planted in lines of 5 m between them and 20 m between rows.

A higher density of trees is acceptable for shade-tolerant crops; if the tree products are high in demand, the loss in crop yield due to shade can also be tolerated.

Trees like Acacia spp., which provide light shade, can be planted at a higher density. The same applies to trees that can be pollarded or pruned on top.

Tree-management depends on the tree and crop species and the need for tree products. If the crop demands light, pruning is essential, while shade-tolerant crops can grow under trees that allow filtered sunlight.

Trees used for timber and to reduce light need pruning at a height of 12 to 15 m, but shade tolerance and production of poles need lower and less frequent pruning. The land-use pattern and post-harvest grazing and burning need to be considered before recommending tree planting in cropland.

It is easy to establish trees as the seedlings benefit from weeding and protection of the crop. Several products can be harvested, while the trees also improve the soil, reduce wind-speed and improve the microclimate.

Too many trees can cause reduced yields due to shade, and birds may also threaten crops. Trees with shallow roots should be avoided, as well as trees that cannot be pruned.

Farm forestry, particularly woodlots and boundary planting

Woodlots include Eucalyptus spp, Grevillea robusta (silky oak) and Casuarina lusitanica planted for timber, poles and fuelwood. Boundary planting of basically the same species is used for farm boundary demarcation, timber, poles, fuelwood, aesthetics and shade.

Fruit orchards in homestead planting

Planting in fruit orchards include mangoes, oranges and lemons, avocados, plums and Macadamia nuts, to mention some. They are planted for their nutritional diversity and the income from sales they can generate.

Alley cropping or hedgerow intercropping

For this purpose, Calliandra calothyrsus (red powder puff tree),Gliricidia sepium (mother of cacao), Leucaena spp, Tithonia diversifolia (marigold tree), and Acanthus pubescens, are planted to improve and protect soil and as livestock feed.

Homestead planting and fencing

Fruit trees, including mangoes, citrus fruits, guavas and black plums are planted in homestead gardens. Timber trees like Grevillea robusta, Eucalyptus spp, sand Podocarpus spp (yellowwood or pine), Casuarina equisetifolia, (ironwood), among others, are also planted, as well as shade and ornamental trees like e.g. Croton Megalocarpus, and Spathodea campanulate (African tulip tree). These trees provide fruit, timber and fuelwood, shade, and a beautiful backdrop.

Riverbank, lakeshore and terrace stabilisation

Mostly indigenous and fruit tree species are planted for land and riverbank protection and conservation, as well as for livestock fodder, fuelwood, fruit for food, and live fences.

Context of agroforestry practice in the humid lowlands

Agroforestry practices in the humid lowlands are practiced in the following context:

Declining soil fertility in areas like western Kenya

Agroforestry technologies, such as short-rotation improved fallows to reverse soil degeneration and to improve crop yields in western Kenya from early1990 to 2000 failed to hit the target.

However, the problem still persists but if agroforestry technologies can be integrated into the crop farming business, it could bolster soil fertility.

Shortage of fuelwood and construction materials

The continued use of fuelwood, which is the primary source of energy for nearly 90% of rural households, as well as the high demand for wood in the construction industry, are major drivers for agroforestry.

The use of fuelwood is a major cause of natural resource degradation. It is therefore essential that on-farm tree planting is done. A welcome side effect is that it helps restore land and provide some mitigation against climate change.

Shrinking land sizes and forage shortage

The average land holding in these areas is about 2,5 acres (little more than a hectare). Crops are raised on most of the land, leaving little or no space for livestock grazing. Stall feeding of livestock with crop residues and natural grass is supplemented with fodder shrubs such as Calliandra, which can be planted on the farm boundary as a live fence, soil conservation structures or as a hedgerow to increase productivity.

Source references

Agroforestry in Kenya (2024) Tracextech. https://tracextech.com/agroforestry-in-kenya/

Tengnäs B. (1994.) Agroforestry extension manual for Kenya. Nairobi: International Centre for Research in Agroforestry. Agroforestry extension manual for Kenya.

World Agroforestry Centre. UDC: 634.0.26:374.6(676.2) ISBN 92 9059 116 1. https://apps.worldagroforestry.org/Units/Library/Books/Book%2006/html/publisher.htm?n=1

Wanjira, E.O., Muriuki, J. (2020) Review of the Status of Agroforestry Practices in Kenya. Background study for preparation of Kenya National Agroforestry Strategy (2020 – 2030) World Agroforestry Centre. https://www.ctc-n.org/system/files/dossier/3b/A%20review%20of%20agroforestry%20status%20of%20Kenya.pdf