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Soil health key to successful farming

Friday February 28 2014

Two weeks ago, President Kenyatta launched the first national soil test results, making it possible for farmers across the country to know the suitability of their areas for maize growing.

We spoke to Isaiah M. Tabu, a Professor of Agronomy at Egerton University who told us that knowing your soil holds the key to your success as a farmer.

What is the status of soil fertility in Kenya?

Our soil fertility has been declining over the years. Indeed more than 60 per cent the farms in the Kenyan Highlands are short of Nitrogen and Phosphorus.

What would you say are the characteristics of a healthy soil?

A healthy soil is one which is physically, chemically and biologically sound. By biological soundness of soil, we mean the soil organic matter.


Does it have enough organisms to decompose and release nutrients? By chemical we mean does it have the adequate amount of nutrients in the right ratios? By physical we mean the soil structure and texture which allows aeration.

Why are our soils degraded?
Our soils are degraded because of poor management and soil erosion. Our soils are degraded when we are not returning organic materials into the soil. It (degradation) also occurs when our soil is exposed to water and soil erosion. All this is reflected in declining crop yields.

So what do we need to do?
What is needed is a combination of methods that will improve the chemical, biological, and physical conditions of the soil. We need a combination of organic and inorganic fertiliser.

How are soils under intensive horticultural production affected by the farming practices?
Horticulture comprises vegetables, fruits and flowers, which are continually harvested, and thus continuously removed from the soil. Continuous use of large amounts of inputs also results in pollution of the environment and water masses. It implies the mining of soils and thus making them prone to nutrient loss and acidification.

What parts of the soil are critical for crop production?
Top soil (0-15 cm deep). Annual crops get their nutrients replenished as roots hairs are in the top soils. And this is critical for nutrients. But the sub soil (15-30 cm) is also important for anchorage and depending on the soil profile the nutrients get washed down.

What types of fertiliser is used in Kenya?
We have the inorganic fertiliser, which can be straight or compound. In Kenya, we have up to 12 different types. They include DAP, Urea, CAN, 20:20:0 and so on.

Inorganic fertiliser is good because it is concentrated and is readily available, but is prone to leaching, which quickly acidifies the soil and pollutes the environment.

Organic fertilisers include farmyard manure, compost, cow dung and green manure. They may not be quickly available nor is it concentrated, but they help in building the biological and physical components of the soil, which improves water holding capacity.

What is the level of fertiliser use in Kenya?

It is very low. It is about 10kg/ha compared to the recommended 150 kg. Yet there are places in Western Kenya, for instance, where you have no yields without fertiliser. And even with fertiliser you get barely less than one tonne a hectare.

At one place in Kakamega when we used a combination of lime, organic and inorganic fertiliser we got more than 5,000kg per acre.

Most of the farmers are getting one tonne per acre, yet they can get up to six tonnes. Suffice it to say, correct and effective use of fertiliser holds the key to higher productivity and food security in Kenya.

What do we need to do?

We need to promote fertiliser use by increasing access by farmers through increasing quantity and reducing cost. We can also do this by providing site-specific recommendations through education and improved soil testing.

Why is it important to test soil?

In order to determine the type of nutrient required by the crops, the rate required by crop and the form of fertiliser that is ideal. This will lead to improved nutrient use, efficiency and productivity.

Is soil testing affordable to the common farmer?

The cost of soil testing varies with the nutrient and place. It ranges from Sh1000 to Sh2000 per sample. Considering the amount of improved output resulting from using the right fertiliser type, rate and form, soil testing is not expensive in the long run. But we need more testing centres. We need to move closer to the farmer.

How is soil sampling done?
Fields varying in fertility are mapped and points for sampling identified based on a W and Z structure. By moving in the pattern of the shapes of these letters you ensure you have taken a representative sample. Be careful to put the subsoil and the top soil layers separately.

Where do I take soil for testing?

After preparing the soil sample, it is physically delivered or posted to the soil testing centre.

Various centres exist including the Kenya Agricultural Research Institute offices, institutions of higher learning such as Egerton University and private companies like Mea Ltd labs in Nakuru. The Tea Research Foundation in Kericho also tests soil for tea farms.

Are the results easy to comprehend by farmers?

The results may not be easily understood by a layman, but they are usually interpreted into a language a farmer can understand.

How often should soil be tested?

After about four or five years or when changing from one crop to another. Sandy soil takes two to three years, while clay soil can go up to three to four years. It is very important if you are changing the crop of the system to test the soil. Actually in developed countries, they do soil testing every season.

Do we have adequate expertise and facilities for soil testing?

There are several soil testing centres in Kenya. Their performance, however, varies. Expertise exists across the country, but may not be enough if the demand for the service is high.

What has Egerton University done to support this initiative?

Egerton University is offering training at both undergraduate and post-graduate levels on soil management, environment, land use management and so on.

We also have a number of outreach projects on this and other agricultural matters in the communities around our campuses, as well as consultancy services.

What soil management methods can be used to improve soil quality?
Chemical and biological characteristics can be improved through addition of external inputs as inorganic or organic fertiliser. Physical condition of the soil can also be done by adopting minimum tillage practices and use of the right cropping system like intercropping.

How severe is soil erosion in Kenya?
Severity varies with the soil type and area. Generally, it has been increasing because of the increase of land use per capita. Continuous cultivation and cultivation in areas not recommended for cultivation has also led to increased landslides. Rivers and dams are getting silted. It is a leading cause of food insecurity in Kenya.

How can farmers increase their soil moisture?
By building physical structures such as terraces and reduced tillage and by employing biological methods like cropping systems and use of crop residues.

How will the national soil testing exercise recently launched by the President affect productivity in Kenya?
This means the country is now able to know the types of soils, potential, requirements for management. This will result in efficient resource use and cleaner environment. It means now that farmers can access the right information on soils and fertiliser to use. The overall impact is improvement in the productivity as a result of using the right information.

What is your opinion on the fertilizer factory to be set up?
We will get the right type of fertiliser close to the farmer. If we are thinking of high specific soil fertility management, then it is important we have it. We have only been managing to blend fertiliser like what Mea Ltd has been doing, but we need to go the whole hog and produce our own inorganic fertiliser in large scale for it to be economical.
It means people will also have jobs. As to whether it will reduce the cost depends on whether we are going to produce for large scale.

Interview by Francis Mureithi