SCIENCE CORNER
New Science
February 2022
Liming agricultural soils in Western Kenya: Can long-term economic and environmental benefits pay off short term investments? Agricultural Systems 190 (2021): 103095
Hijbeek, R., van Loon, M.P., Ouaret, W., Boekelo, B., van Ittersum, M.K. 2021.
Summary by Dobermann, A.
Soil acidification is a major constraint to increasing crop yields, but it is often also a long-term consequence of agricultural land use. At present, only 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 is 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 in Western Kenya, with or without fertilizer use. For a soil pH of 5, applying 2 t/ha lime resulted in a 57% increase in maize yields (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 thereafter. 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.
Classic Plant Nutrition Paper
Predicting the lime requirement of soils under permanent grassland and arable crops. Soil Use and Management 5 (2): 54-58.
Goulding, K.W.T., McGrath, S.P., Johnston, A.E. 1989.
Summary by Dobermann, A.
In Europe, liming soils with chalk, limestone, bones and other materials became a common farming practice centuries ago because farmers observed clear benefits for sustaining or increasing crop yields. The question of how much lime to apply, how often, in what form, and how has interested practitioners for a long time. Recommendations were mostly based on sampling and analyzing the soil. This short paper presents a different solution: a model that gives a precise lime requirement based on estimated annual losses of calcium by leaching and the response of the soils to past lime applications. On just four pages, three Rothamsted soil scientists elegantly manage to summarize results of decades of liming experiments conducted in the UK. They show that the magnitude and duration of the effect of lime applications varied with soil type, initial soil pH, fertilizer nitrogen application, and the crop grown. Simple equations for each situation were linked to form an empirical model which predicts the amount of lime needed to reach the desired pH. The model later became known as RothLime and it is still available as a simple online app at https://www.rothamsted.ac.uk/rothlime. Over time, numerous models and decision support systems to guide acid soils management have been developed worldwide. However, the logic, simplicity and robustness embedded in RothLime make this paper a classic paper for me. The paper also demonstrates the great value of well-designed and carefully conducted long-term field experiments for addressing practical problems. Such studies and well-validated decision aids will also be required for tackling the soil acidity challenge in sub-Saharan Africa, but with extended functionality to also consider factors such as infrastructure, capital requirements and return on investment.