Farmers are increasing their crop yield by up to 500 per cent by applying lime to reduce the acidity of Kenya’s most productive but quickly acidifying soils that have seen their crop yields reduce by a quarter.
According to the FAO, 60 per cent of Kenya’s acid soils in are in Central, Western, Rift Valley, and Eastern Kenya. Studies have shown that 5.41 kilograms of acidity is being added per hectare each year to soils in these regions that contribute to majority of the country’s agriculture production. These soils are usually deep and well-drained and in areas that receive over 2,000mm of rainfall each year making them perfect for farming. However, this high soil acidity has led to poor crop yields as most crops get the most nutrients and perform best when the soil has a 6.0 – 7.0 pH range. Applying lime on these soils has been shown to be the quickest, cheapest, and easiest way to reduce this soil acidity compared to the other alternatives which are putting organic matter into the soil and shifting to just growing acid-tolerant crops. Depending on the initial acidity of the soil and its characteristics, the crop, and the amount of lime used, liming raises farm yields fivefold.
Farmers who used two tonnes of lime in fertilie soils at Soy in Uasin Gishu which had a pH of 4.0 saw their maize yields increase by 525 per cent in 2017 and 22.7 per cent in 2018. Their wheat harvests increased by 22.7 and 20 per cent during the same time.
At the Agriculture Training Centre in Embu, soils with a pH of 5.06 that had two tonnes of lime applied on them saw soybean yield go up 42 per cent in the first year.
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In Kuinet, Uasin Gishu, adding two tones of lime per hectare in soil with a pH of 5.0 increased the yield of the Amy French bean variety by 12.5 per cent but did not increase the output of the Samantha variety in the first season. The following year, yields of Samantha increased by 47.8 per cent but Amy did not see any increase in yields.
“Based on all the experiments done in Kenya, we can see a clear pattern where feeding acidic soils with moderate amounts of lime, 2.0 to 2.2 tonnes per hectare, every year to avoid over-liming is profitable and gives farmers a net positive return.
These positive returns also keep coming if farmers use lime together with inorganic and organic fertilisers, grow high-yielding crop varieties, and carry out better agronomic practices on their farms” mentioned KALRO Soil Scientist Anthony Esilaba.
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According to the scientist, the higher the amount of lime applied, the longer effective it is. “It is also important to first get a soil test for soil pH and exchangeable acidity and share this information with your extension office to get the best liming recommendations based on the characteristics of your soil and what you are looking to grow,” he added.
To determine if your soil is acidic and needs liming, the first step is to test your soil. This is done by collecting a sample of your farm’s soil.
For crops, sampling is done from the topsoil– soils first top layer– from zero to 20 centimeters deep.For deep-rooted crops such as trees sampling is done at the subsoil– 20-50cm deep.
According to the Soil Acidity and Liming Handbook for Kenya, a soil sample should be collected from a mixture of individual samples from multiple locations on the farm. The sub samples should be taken not just of places on the farm that are far away but also of areas that have different soil characteristics such as productivity, drainage, soil texture, terrain of the land and past management.
A good representative soil sample should have 10 and 20 sub-samples. The more the sub-samples, the more reliable a soil sample is.
For smallholder farmers in Central, Western, and Eastern Kenya, nine sub samples for 0.5-hectares of land have been shown to be enough in determining the soils pH.
A soil pH test can cost as little as Sh100 at the Kenya Forestry Research Institute in Nairobi (0724 259781/2, 0722 157414).
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The major hinderance to Kenyan farmer applying lime on their shambas remains the cost. A 50 kg bag of lime costs Sh2,800. Agricultural lime which also requires to be used in large quantities is expensive to transport because of its bulkiness.
According to One Acre Fund, farmers also struggle to interpret the application requirements for the lime bags.
To reduce the cost of lime farmers are advised to combined it with and organic materials such as well dried farmyard manure and/or composts which also reduce the soils acidity more slowly than lime. Inorganic fertilisers also improve the soil’s fertility.