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Soils of Kenya: what is in your ground, and what it needs.
Most Kenyan farm soils are acidic, low in organic matter and short of phosphorus, and those three problems feed each other. This guide explains the pattern, shows where it is worst, and tells you how to find out what your own soil needs before you spend money on inputs.
Soils that have been asked for more than they get back
Most of Kenya, around four-fifths or more of its land, is arid or semi-arid rangeland. The farmland that feeds the country is concentrated in the wetter highlands and midlands, and it is under heavy pressure.
Nutrients are leaving faster than they come in.
KALRO estimates Kenyan soils lose about 21 kg of nitrogen, 8 kg of phosphorus and 43 kg of potassium per hectare each year, while farmers apply only about 12 to 32 kg of nutrients per hectare per year in total. Shorter fallows, as populations grow, have sped the decline.
SOURCES: HEINRICH BÖLL STIFTUNG KENYA, “KENYA’S DIVERSE SOILS”; KALRO, “OVERVIEW OF SOIL FERTILITY AND AVAILABLE SOIL TESTING PROGRAMS IN KENYA” (IFDC); ORGANIC RESOURCE MANAGEMENT IN KENYA (OFRA, CHAPTER 7)
Three problems that travel together
Acid soil
Acidity locks up phosphorus and makes other nutrients, including potassium, harder for plants to take up. Even fertilizer you pay for can be wasted.
Low organic matter
In tropical heat, organic matter breaks down fast and is not replaced. Soil loses structure, holds less water and responds poorly to fertilizer.
Low phosphorus
Many soils are short of phosphorus to begin with, and acidity makes it worse. Zinc, boron and other trace nutrients are also commonly short.
What this looks like in the field.
In Kenya’s central highlands and western region, studies found that even heavy nitrogen fertilizer on acid, low-organic-matter soil did not push maize yields above about two tonnes per hectare. Soils with more organic carbon and a pH above 6 reached up to 3.5 tonnes per hectare with less fertilizer.
SOURCE: HEINRICH BÖLL STIFTUNG KENYA, “KENYA’S DIVERSE SOILS”
What the soil is like where you farm
Soils change from county to county, and often from farm to farm. Treat this as a starting point, then test your own land.
Western Kenya
The most acidic farmland in the country. Many soils here are old and weathered, so they are low in nutrients, though they can yield well with added nutrients and erosion control. On KALRO’s western trial sites, topsoil organic carbon was below the adequacy level on 75 to 100% of farms, and phosphorus was low on 60 to 87% of farms in Bungoma, Kakamega, Nandi and Bomet.
What helps: a soil test, lime where pH is low, compost or manure to rebuild organic matter, and phosphorus from a source your test supports.
Central highlands
Volcanic soils that are porous and hold water well, but are acidic and prone to erosion. They grow tea, vegetables, potatoes, bananas and coffee. In a study of 198 potato farms in Nyandarua and Meru, soil pH ranged from strongly to weakly acidic, boron was below the critical level on 80 to 87% of farms, and phosphorus was low on 46% of Meru farms and 85% of Nyandarua farms.
What helps: compost and cover to protect against erosion, lime where tested pH is low, and attention to boron and phosphorus.
Rift Valley highlands
Acidity is also serious in parts of the Rift Valley. Kericho and Narok, along with Kakamega, Bungoma and Nandi, had the largest total lime requirements in a national study. Many of the same issues as the west apply: low organic carbon and low phosphorus.
What helps: test first, since conditions differ widely across the Rift, then combine lime where needed with organic matter.
Semi-arid and arid lands
Soils include Luvisols, Acrisols and Vertisols. Heavy clays in flat, flood-prone areas crack when dry. Salt-affected soils cover about 40% of Kenya’s arid and semi-arid regions, which harms drainage and crops. Typical crops are sorghum, millet, cassava, beans, pigeon pea, cowpea, green gram and groundnut.
What helps: organic matter to hold water, better drainage and water management, and gypsum with organic manure on sodic soils. Heat breaks organic matter down quickly, so apply it often.
Coastal lowlands
Well-drained sandy soils over much of the area, fertile loams in the Taita Hills, and river-deposited silts in the Tana and Sabaki valleys. Deep, grey, poorly drained saline soils in dune and mangrove areas are not suited to crops.
What helps: sandy soils hold little water or nutrients, so regular compost makes a large difference. Avoid cropping the saline areas.
SOURCES: BÖLL KENYA; OFRA KENYA CHAPTER; KALRO (IFDC); MUGO ET AL. (2020), SCIENTIFIC REPORTS; MUINDI ET AL. (2025), SOIL ACIDITY IN KENYA, TROPICAL AND SUBTROPICAL AGROECOSYSTEMS
Where acid soil is most widespread
A national study mapped acid soil across counties. These bars show the share of each county’s land with soil pH of 5.5 or below.
Among registered farming households, about 84% in Kisii, 80% in Nyamira and 77% in Murang’a were affected. Acid soil was found across 29 counties, mainly in the Western, Rift Valley and Central regions.
Why do you see both “63%” and “13%”?
They measure different things. The 63% figure is the share of arable farmland that is acidic. The 13% (about 7.5 to 7.7 million hectares) is the share of all of Kenya’s land, most of which is dry rangeland. Neither means your field is acidic. Only a soil test tells you that.
SOURCES: MUINDI ET AL. (2025), “SOIL ACIDITY IN KENYA”, TROPICAL AND SUBTROPICAL AGROECOSYSTEMS; BÖLL KENYA. COUNTY AVERAGES HIDE BIG DIFFERENCES BETWEEN FARMS.
Lime, compost and fertilizer work as a team
No single input fixes all three problems. Each handles a different one.
- Test your soil firstIt tells you whether acidity, phosphorus or organic matter is the real limit on your farm, so you spend where it counts.
- Lime if the soil is acidicKALRO guidance is to manage acidity with lime where soil pH is below about 5.2, and 5.5 is the critical level for maize. In earlier trials on acid soils in western Kenya, lime at 4 tonnes per hectare raised maize yields several-fold, though results vary with soil and rate.
- Add compost or manure for organic matterThis rebuilds structure, water holding and soil life, and helps the soil hold on to the nutrients you add. It works best alongside the other steps, not instead of them.
- Feed the crop with balanced nutrientsUse fertilizer (organic or mineral) according to your soil test and crop. Compost is bulky, so it cannot supply everything a hungry crop needs quickly.
What a tonne of organic material is worth
A rough guide to the fertilizer each material can replace, per tonne applied.
| Material (per tonne) | Urea | DAP or TSP | KCl (potash) |
|---|---|---|---|
| Farmyard manure (dry) | 5 kg | 3 kg | 2 kg |
| Compost | 8 kg | 3 kg | 3 kg |
| Dairy or poultry manure (dry) | 9 kg | 4 kg | 5 kg |
| Fresh leaves, e.g. tithonia or grevillea prunings | 4 kg | 2 kg | 2 kg |
Real values vary with how the material was made and what went into it. The numbers show why compost is mainly a soil builder: a tonne replaces only a small amount of fertilizer, but it improves the soil that fertilizer works in.
SOURCES: KALRO (IFDC); BASIS/UC DAVIS ON LIME AND SOIL TESTING IN KENYA; ORGANIC RESOURCE MANAGEMENT IN KENYA (OFRA, CHAPTER 7)
How to take a soil sample
In one recent survey of Kenyan farmers, only 11% had ever had their soil tested. Ideally, test about every three years. A good result depends on a good sample.
- Pick the timeSample after harvest or before planting. Don’t sample right after applying lime, fertilizer or manure.
- Walk the fieldTake samples along a diagonal or zigzag line across the field. Use a soil auger if you have one, or a clean spade or panga.
- Take 15 to 20 spotsAt each spot, clear the vegetation and take a slice of soil from a vertical cut 15 to 25 cm deep. Put each slice in a clean plastic bucket. Larger fields need more spots.
- Avoid unusual placesSkip old manure heaps, fence lines, swampy spots, the edges near trees, and places that differ from the rest of the field. If part of the field is clearly different, sample it separately.
- Mix, dry, bag and labelMix everything in the bucket thoroughly, dry and crush it, then put a sub-sample in a clean polythene bag. Label it with your name, address, field and date.
Reading your results
| Result | What it suggests |
|---|---|
| pH below 5.2 | KALRO guidance: liming is needed to manage acidity. |
| pH below 5.5 | Below the critical level for maize. Acidity is probably limiting your yield. |
| Organic carbon below about 2.7% | Below KALRO’s adequacy level for topsoil. Most Kenyan farm soils are below this, so compost or manure is needed. |
| Phosphorus, potassium, zinc, boron | Labs use different methods, so numbers are not directly comparable. Ask your lab what the critical level is for its method. |
The cheapest unsubsidised test in that survey cost about KES 1,350, which is a barrier for many farmers. Group testing across neighbouring farms, or testing representative plots, can bring the cost per farmer down. Because labs differ, use the same lab when you want to compare results over time.
SOURCES: BIOVISION AFRICA TRUST SOIL SAMPLING GUIDE; KALRO (IFDC); BASIS/UC DAVIS, “LOW WILLINGNESS TO PAY FOR SOIL TESTS LIMITS LIME POTENTIAL”
Questions people ask
If I use compost, do I still need lime?
If your soil is strongly acidic, probably yes. Compost improves the soil but does not usually correct strong acidity on its own. A soil test will tell you.
Is my farm acidic if my county is on the list?
Not necessarily. County figures are averages, and soils differ between farms and even between fields. Test your own soil.
How often should I test?
Ideally about every three years, and again if yields drop or you change what you grow.
Does too much fertilizer make soil more acidic?
Overuse of synthetic fertilizers has made acidity worse in some areas, and continuous cropping without organic inputs adds to it. Balanced fertilizer combined with organic matter is the safer path.
Where can I get my soil tested?
Both public laboratories, including KALRO, and private labs offer soil testing. Methods differ, so ask what the lab measures and how it reports results. We can help you interpret your report.
Turn your soil results into a plan
Send us your soil test results and tell us what you grow. We’ll help you read them and plan lime, compost and fertilizer together.