In Kenya, around 13% or 7.5 million hectares of soils are acidic, which approximates to 63% of the country's arable land. Soil acidity is particularly prevalent in the Central, Western, and Rift Valley regions, which are the primary food baskets of the country. There are also pockets of soil acidity in some parts of the Eastern and Coastal regions. This issue clandestinely undermines crop productivity and poses a significant threat to national food security.
Soil acidity is measured by its pH level. A neutral pH sits at 7.0, with anything below considered acidic and anything above considered alkaline. Acidic soils (pH below 7.0) contain high concentrations of hydrogen ions (H+). These H+ ions disrupt nutrient availability, hindering the plant's ability to absorb essential elements like phosphorus, calcium, and magnesium.
Various natural phenomena and human activities contribute to the development of soil acidity. These include the impact of heavy rainfall and leaching, the use of nitrogenous fertilizers releasing H+ ions during the nitrification process, the decay of organic matter generating H+ ions, and the lime-like elements depletion from soil due to crop production.
The impact of soil acidity varies across crops. While tea and coffee thrive in slightly acidic soils (pH 5.5-6.5), excessively acidic conditions can stunt growth and affect yield and quality. Maize, Kenya's staple food, tolerates moderate acidity (pH 5.0-6.0), but severe acidity significantly reduces yields. Fruits and vegetables generally prefer slightly acidic to neutral soils (pH 6.0-7.0), with excessive acidity leading to stunted growth and poor fruit quality.
Several strategies have been documented for managing acid soils in Kenya, including liming, use of organic materials, integrated soil fertility management (ISFM), and cultivation of acid-tolerant crop varieties. However, majority of farmers do not have access to these soil acidity management options. Liming, the cornerstone strategy, is the most common and effective method used. It involves applying calcium carbonate (CaCO3) or other liming materials to directly neutralize soil acidity. This process increases soil pH, making essential nutrients like phosphorus, calcium, and magnesium more readily available for plant uptake. Beyond its direct effect on pH, liming also improves soil structure by flocculating clay particles, which enhances aeration and water infiltration.
While the agricultural advantages of liming are widely recognized, its implementation remains limited in Kenya. As of 2023, the adoption of lime by farmers was notably low, ranging between 1% and 8%. Although substantial research on lime application has been conducted in Kenya, the scope of crops studied is relatively narrow, with a predominant focus on maize, the staple food crop. These studies reveal varying yield responses to liming, ranging from 0 to > 400%. The degree of yield increase depends on factors such as initial soil pH, crop type, soil characteristics, and lime application rate. Thus, it is imperative to conduct soil tests for pH and exchangeable acidity before recommending liming practices. Moreover, lime application should be supplemented with other nutrients, particularly macronutrient NP and NPK fertilizers, which are typically deficient in most smallholder farms.
Ujuzikilimo has been leading the way in addressing soil acidity in Kenya, achieving significant agricultural progress. By offering advanced insights into soil acidity management through soil testing to determine NPK levels and providing personalized agronomy recommendations, UjuziKilimo equips farmers with essential knowledge about lime application and fertilizer use. This initiative has had a positive impact on more than six counties, including Homabay and Kisii. In Homabay, soil tests conducted using SoilPal revealed pH levels ranging from 5 to 7.99, with most areas falling between 5 and 6.99. Similarly, in Kisii, pH levels ranged from 4 to 7.99. Farmers in these regions received tailored agronomy recommendations focusing on crops such as maize, beans, cowpeas, spider plant, banana, groundnuts, and cotton. This initiative has reached more than 10,000 farmers, addressing acidity issues, enhancing soil health, and boosting crop yields.
In essence, overcoming soil acidity in Kenya necessitates a united front. Collaboration between farmers, researchers, and policymakers is vital for crafting and implementing a national action plan to rehabilitate acidic soils. From lime application and organic material incorporation to integrated soil fertility management and the cultivation of acid-tolerant crops, each solution plays a crucial role in restoring soil health, enhancing crop yields, and ensuring the long-term sustainability of agricultural systems. By embracing these solutions and implementing them effectively, Kenya can navigate the challenges posed by soil acidity and pave the way for a resilient and prosperous agricultural system.