Soil acidity status and lime requirements for agricultural lands in Kenya

Background. Soil acidity is a major soil health challenge that impacts agricultural productivity in Kenya while information on its national extent and severity remains limited. Objective. To determine national extent and spatial distribution of soil acidity, estimate the number of farming households affected and quantify lime requirements for acid soils within the Country. Methodology. This was achieved through application of data-driven approach, utilizing existing soil data collected at 0 -30 cm depth between 2012 and 2024, gridded environmental GIS layers, digital farmer registry data and geospatial analysis techniques. Soil pH and exchangeable acidity were then integrated to map acidity classes, estimate affected land area and households, and compute lime requirements for soils with pH≤5.5. Results. Soil pH (H2O) across the Agricultural soils ranged from 3.7 to 10. 8. Approximately 13.29% (7.7 million ha) of the national land area was affected by soil acidity (pH ≤ 5.99), comprising < 1% (< 100 ha) extremely acid (pH ≤ 4.5), 0.2% (0.12 million ha) very strongly acid (pH 4.51 – 4.99), 5.5% (3.16 million ha) strongly acid (pH 5.00 – 5.50) and 7.6% (4.4 million ha) moderately acid (pH 5.51 – 5.99). The soil acidity problem spanned across 29 counties, with higher severity in Western, Rift Valley and Central Kenya. The counties with largest proportion of acidic land were Kisii (100%), Nyamira (100%), Vihiga (93%), Nandi (91%) and Kakamega (91%). Out of the 6.4 million digitally-registered farming households nationwide, Kisii County had the highest number (184,103) and proportion (83.6%) affected. Additionally, lime requirements at pH <5.5 were observed to vary widely ranging from 269 metric tons (MT) in Kakamega to 8 MT in Kisumu, and 0.58 ± 0.08 t ha-1 in Nakuru to 1.51 ± 0.07 t ha-1 in Nyamira. Implications. Obtained spatially-explicit soil acidity maps and lime requirement estimates provides evidence for supporting government and stakeholders in operationalization of soil health interventions, lime use policies, subsidy programs and prioritization of acid soil remediation and research. Conclusion. This study provides a nationally representative, spatiall assessment of soil acidity and lime requirements, offering critical guidance for targeted remediation and integrated soil health management approaches.