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This review focused on the efforts made to understand and manage Kenyan acid soils by use of inorganic, organic materials (OMs) and crop germplasms tolerant to soil aluminium (Al) toxicity and/or low soil available phosphorus (P). Kenyan acid soils which occupy 13% of the total land area were developed through parent materials of acid origin, leaching of base cations and use of acid forming fertilizers. They are high in Al (>2 cmol Al/kg and > 20% Al saturation) and low in soil available P (< 5 mg P/kg soil) due to moderate-high (107-402 mg P/kg) P sorption, hence crops recover only 9.6 to 13.5% of the P fertilizer. Application of lime, P fertilizer and OMs increases soil pH, available P and reduces Al toxicity on Kenyan acid soils. Lime, P fertilizers and OMs have increased maize grain yield by 5-75, 18-93 and 70-100%, respectively on Kenyan acid soils. Similarly, deployment of crop cultivars tolerant to Al toxicity and/or low soil available P increases crop yields. However, lack of knowledge on the importance of lime, credit to purchase farm inputs, crop varieties tolerant to soil acidity constraints and inadequate amounts of OMs limits crop yield on Kenyan acid soils.

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Low soybean yields in western Kenya have been attributed to low soil fertility despite much work done on nitrogen (N) and phosphorus (P) nutrition leading to suspicion of other nutrient limitations. To investigate this, a nutrient omission trial was set up in the greenhouse at the University of Eldoret-Kenya to diagnose the nutrients limiting soybean production in Acrisols from Masaba central and Butere sub-Counties, and Ferralsols from Kakamega (Shikhulu and Khwisero sub-locations) and Butula sub-Counties and to assess the effect of liming on soil pH and soybean growth. The experiment was laid out in a completely randomized design with ten treatments viz; positive control (complete), negative control (distilled water), complete with lime, complete with N, minus macronutrients P, potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S) and with, micro-nutrients boron (B), molybdenum (Mo), manganese (Mn), copper (Cu) and zinc (Zn) omitted. Visual deficiency symptoms observed included interveinal leaf yellowing in Mg omission and N addition and dark green leaves in P omission. Nutrients omission resulted in their significantly low concentration in plant tissues than the complete treatment. Significantly (P≤ 0.05) lower shoot dry weights (SDWs) than the complete treatment were obtained in different treatments; omission of K and Mg in Masaba and Shikhulu, Mg in Khwisero, K in Butere and, P, Mg and K in Butula. Nitrogen significantly improved SDWs in soils from Kakamega and Butula. Liming significantly raised soil pH by 9, 13 and 11% from 4.65, 4.91 and 4.99 in soils from Masaba, Butere and Butula respectively and soybean SDWs in soils from Butere. The results show that, poor soybean growth was due to K, Mg and P limitation and low pH in some soils. The results also signify necessity of application of small quantities of N for initial soybean use.

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