Soil acidification is a long-term consequence of agricultural land use and becomes a major constraint to increasing crop yields. At present, farmers in Africa use lime or other materials to improve soil health.
Summarizing data from 26 field experiments, this study assesses if liming acid soils are economically and environmentally viable at different levels of intensification of maize cultivation in Western Kenya. Liming consistently increased maize yields on soils with an initial soil pH between 4.0 and 5.7, with or without fertilizer use.
Starting at a soil pH of 5, applying 2 t/ha lime increased maize yields by 57% (from 2.3 to 3.6 t/ha) in the first year after application. Including all costs, liming was only profitable when it was combined with fertilizer (N, P) application. In that case, the observed yield increases also offset the liming-associated greenhouse gas emissions per ton of grain maize. These results demonstrate substantial co-benefits of liming and fertilizer application for food security and the environment in acid soils of the Tropics, but they also illustrate a huge challenge. Liming all acid cropland soils in sub-Saharan Africa to pH levels deemed sufficient for most crops (e.g. at least pH 5.5) would require several hundred million tons of lime, and regular additions afterwards. These are investments that smallholder farmers alone cannot make.
Liming is, however, an important prerequisite for sustainably increasing crop yields and achieving better returns on investment in fertilizer and other technologies. New efforts are currently ongoing to develop suitable strategies and practical solutions for rehabilitating acid soils in Africa.
