A Basic Guide To Soil and Overview of Kenyan Soil

December 29, 2022 7 min read

Soil is made up of minerals, air, water and organic matter. Every soil has its unique characteristics that are determined by how it was formed. Soil is the medium in which plants are grown. Without soil, we would not survive. Soil is important and must be nurtured and guarded at all costs for ourselves and for generations to come.

Soil Organic Matter

Organic matter comprises living and dead microorganisms, and plant and animal residues in different stages of decay and humus. Organic matter changes what you can do with different soil types such as sandy or clay soils. Soil is the foundation of almost all life on this planet. It is a complex symbiotic system of organic matter, minerals, gasses, liquids and living organisms that together support life. Without organic content in the form of humus and living organisms and microbes, the soil is reduced to inert sand.

Soil Food Web

Understanding your soil composition will help you determine the foundation with which you are working. If you have come across worms, centipedes, slugs, ants, ladybirds, beetle larvae, springtails and more, then this is a sign that your soil food web is healthy. Healthy soils should be teeming with life seen and unseen. All these organisms are one kind of prey to another thus forming food chains known as a soil food web. The soil food web comprises both good guys and bad guys. If you use pesticides in your garden, you don’t just get rid of the bad guys, but some good guys get eliminated too! Pesticides, herbicides, fungicides and fertilizers also create a toxic environment and they change the method by which plants take up nutrients. Chemically fed plants bypass the microbial-assisted method of obtaining nutrients. The microbial populations adjust, and you have to keep adding these chemicals which is a very costly affair for your soils, your pocket, your health and the environment. As such it is best to work with your soil to encourage a healthy soil food web.

How do I know if my soil is any good?

Good question. Good soil is characterized by

Rich dark ‘coffee’ colour
High organic matter (you should be able to see some living creatures such as worms, centipedes, ants and so forth)
Should be able to hold sufficient water for the plants, yet drain well enough when the water is more than the plants need.
Good soil smells good too!

Poor soil is pale, compacts, drains too fast or does not drain well (holds too much water) and can sometimes smell bad.

The appearance however is just a simplistic way of determining the health of your soil so thus we recommend conducting a soil test at least once a year. In Kenya, you can have a soil test done in

Kephis (Kenya Plant Health Inspectorate Service). Their rate ranges between Kshs.2,500 – 3,500 per soil sample. This rate is as of March 2022
KALRO (Kenya Agricultural and Livestock Research Organization). Their rates range from Kshs.500 – 1,500 per soil sample. This rate is at March 2022

The benefit of having a soil test performed at a lab is that you will get to know the precise nutrients available or lacking, and the microbial activities.

Read more about having your soil tested here.

Restoring and Maintaining your Soil

Restoring and maintaining your garden soil is a very intentional yet rewarding activity. The ultimate goal for any gardener or farmer is to restore and maintain a healthy soil food web enticing beneficial organisms to grow and thrive. If you have been using chemicals (or have moved to a piece of land with previous use of chemicals), then this exercise is even more important. One of the tools that you can use to restore your soil food web is compost. Applying compost and mulch to your garden soil is a powerful strategy for restoring your soil food web. Compost is a management tool that is highly effective in feeding microbes that feed the plants. Thus eliminating the need for chemicals.

Mulching using organic matter i.e leaves, grass, wood chips and even cardboard boxes provide a good environment for the soil community’s organisms. These are the carbon-rich and nitrogen-rich materials that when added to a compost pile provide both an energy source and basic building block which makes up about 50% of the mass of microbial cells.

Does Soil Type Matter?

In Kenya, we tend to focus on the colour of the soil to determine if the soil is any good. Red soil is always the ‘hero’ and soil colour of choice and gardeners have been known to import huge volumes into their gardens. This is not necessarily a bad thing, just that it can be unnecessary if you can work with your soil and fix it to have the qualities you need for a successful garden. Of Course, if you are in a new landscape and you have mainly rock and debris from construction activities or have very poor soil then you would have no choice but to import soil.

Kenyan Soils

Kenya has a wide variety of soils resulting from the variation in geology, topography, climate and other factors. Soil profiles have changed over time due to natural and man-made conditions. Some Kenyan soil types include:-

Andosols (young volcanic soils)

Found in areas with high rainfall and steep slopes like Kijabe, the highlands of Kinangop. Andosols have a high water holding capacity, are porous, have high organic matter and are very fertile. This explains the quality of veggies that grow in Kinangop!

Acrisols, Alisols, Lixisols and Luvisols

Found in the drier parts of the highlands, eastern Kenya, some parts of Mt. Kenya and Thika. These soils tend to be low in PH and generally have a poor structure.

Ferralsols

Found in the Trans Nzoia plateau, Kisii the soils are strongly weathered. They have an excellent capacity for holding moisture and are rich in aluminium and iron but low in Phosphorous and Nitrogen. Compost and animal manures are useful in improving these soil qualities.

Nitosols / Nitisols

Found around Mt. Kenya, Central highlands of Kenya and areas of volcanic steep slopes. Given that they are developed from volcanic rocks they are known to have rich organic content, a good capacity to hold moisture content with some level of acidity. They are some of the best agricultural soils in Kenya.

Planosols and Vertisols

Phaeozems

Found in semi-arid and sub-humid areas such as Mwea, Nyanza, Narok, Laikipia plateau and Kisii highlands. These are soils with dark coloured topsoil and subsoil due to the high levels of clay content. They are non-acidic, rich in organic matter and highly fertile for agricultural activities.

Vertisols

Commonly known as Black Cotton Soils, Vertisols are dark and cracking soils with poor drainage.

Kenya has many different types of soils. Note that this is a guide to some of the natural soils. Intensive cultivation, climatic effects, urbanisation, importation of foreign soils and other land uses have altered some of the soil topographical features in some areas.

For purposes of the urban gardener, we shall talk about soils as we know and describe them generally.

Sandy Soils

Sandy soils are commonly found in arid and semi-arid areas of the coastal, northern and north-eastern areas. Sandy soils are highly acidic, low in nutrients, very light and prone to erosion, lose water easily and are highly saline.

These soils are problematic for gardening however can be amended using compost and manure. As sandy soils contain high levels of salt. Adding considerable amounts of compost and manure to sandy soils helps with water retention, adds nutrients, and helps reduce the high levels of salt.

Black Cotton Soil

Black cotton soil is also referred to as clay soil. In Kenya, it is commonly found in some parts of Kajiado, Athi, Mwea, Kano, and Transmara. Black cotton soils tend to have poor drainage and become waterlogged, very sticky when wet, crack when dry and are poorly aerated. Black soils however can be highly fertile and suitable for growing certain crops such as cotton, onions, garlic, sunflower, legumes, and vegetables. You just need to engage with practices such as mulching, carefully watering to avoid over or under watering (a drip irrigation system would work well) as well as continuously adding compost to improve the humus.

Red Soils

Red Soils are mainly found in the highland areas i.e east and west of the Rift Valley. A popular and much-preferred soil because of its many positive properties such as well-draining, rich in nutrients, light and easy to till making them ideal for gardening or farming.

Conclusion

Soil is a very broad scientific topic with lots of details involved. However, as a small-scale farmer or urban gardener, you do not need to worry about knowing every little detail. As long as you understand that just like the human body soil needs to be healthy with the right nutrients to feed your plants and keep them healthy too.

Healthy plants can fight off pests and diseases more than weak plants.

References:

Kenyan Soils

https://infonet-biovision.org/EnvironmentalHealth/Kenyan-Soils

Grace Gershuny and Joe Smillie, Fourth Edition The Soul of the soil

Elizabeth Murphy Building Soil: A Down-to-Earth Approach: Natural Solutions for Better Gardens & Yards

Joseph Kimetu, Job Kihara, Boaz Waswa and Andre Bationo Advances in Integrated Soil Fertility Management in sub-Saharan Africa: Challenges and Opportunities

Muchena F. N and Gachene K. K. Soils of the Highland and Mountainous Areas of Kenya With Special Emphasis on Agricultural Soils.

http://erepository.uonbi.ac.ke/bitstream/handle/11295/43096/Muchena_Soils%20of%20the%20Highland.pdf?sequence=2.