Agro-ecological zones (AEZs) are land units defined on the basis of combinations of soil, land form and climatic characteristics.
There are several systems for describing Agro-ecological zones in the Tropics. In Kenya two are used:
- FAO classification for tropics generally, and
- an older Kenya version which is only applicable in Kenya
Classification of FAO Agro-Ecological Zones
- Wheat in zones: UH 2-3; LH 2-4
- Maize zones: LH 1-3; UM 1-4; LM 1-4 (+5); L 2-4 (+5)
- Hybrid maize in zones: LH 1-3; UM 1-3; LM 1-3
- Unirrigated rice in zones: L 1-3; LM 1-2
- Irrigated rice in zones: L 1-6; (7); LM 1-6, (7)
- Sorghum in zones: UM (1-3), 4-5; LM (1-3), 4-5; L (1-3), 4-5
- Finger millet in zones: LH (1-3); UM (1-3), 4; LM (1-3), 4, (5); L (1-3), 4, (5)
- Groundnuts in zones: LM (1-2), 3-4; L (2-3), 4
- Cotton in zones: LM (2), 3-4; L (2), 3-4
( ) means that in these zones the crop is normally not competitive to related crops (f.i. dwarf millets to maize)
Natural potential of Kenyan agro-ecological zones (AEZs)
- AEZ 0 corresponds to ever wet evergreen rainforest
- AEZ 1 to evergreen rainforest
- AEZ 2 to seasonal rainforest because of one or two dry months
- AEZ 3 has three to five dry months, it corresponds to seasonal semi-deciduous moist forest or a high grass - broad leaved trees savanna
- AEZ 4 corresponds to woodland, it is either deciduous in subzone with unimodal rainfall as towards West Kenya and in Tanzania, or hard-leaved evergreen in bimodal rainfall subzones with two dry seasons as in East Kenya, where plants have hard or hairy leaves to avoid shedding them off twice a year. The grass is up to 1 m high.
- AEZ 5 - the natural vegetation in is a short grass savannah with small leafed thorny trees and bushes.
- AEZ 6 is bush land with very short but still perennial grass, therefore it is suitable for ranching - if the grass (the standing hay for the dry season) is not eradicated by overgrazing.
- AEZ 7 indicates Semi-desert
- AEZ 8 full desert
Implications of management on agro-ecological zones
- In AEZ 3 it is necessary to avoid burning which kills the regrowth of trees and ecologically valuable bushes. But the main danger here is overgrazing which puts the balance between grass and bushes to the bush side. Bush encroachment can finally finish the grazing potential.
- This is the same danger in AEZ 4 and 5 but with shrubby species (shrub encroachment, thorny in AEZ 5). In the first stage, poisonous or bitter herbs not eaten by livestock thrive abundantly, leading to some sort of "green degradation".
- In AEZ 6 the eradication of grass by overgrazing promotes at first dwarf shrubs (dwarf shrub encroachment), then in the better subzones thorny low shrubs grow up.
Information Source Links
- FAO (1996). Agro-ecological Zoning Guidelines. FAO Soils Bulletin 73. Rom. www.fao.org
- Sombroek, W.G., Braun, H.M.H. and van der Pouw, B.J.A. (1982). Exploratory Soil Map and Agro-Climatic Zone Map of Kenya, 1980. Scale: 1:1'000'000. Exploratory Soil Survey Report No. E1. Kenya Soil Survey Ministry of Agriculture - National Agricultural Laboratories, Nairobi, Kenya.