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 questions of how much lime to apply, how often, in what form, and with which technique has interested practitioners for a long time. Recommendations were mostly based on sampling and analyzing the soil.
This short paper presents 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 summarize the results of decades of liming experiments conducted in the UK. They show that the magnitude and duration of the effect of lime applications vary with soil type, initial soil pH, fertilizer nitrogen application, and the grown crop.
Based on the results from each situation, the authors built an empirical model to predict the amount of lime needed to reach the desired pH. The model later became known as RothLime which is still available online.
The paper further 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 be required when tackling the soil acidity challenge in sub-Saharan Africa, while additional factors such as infrastructure, capital requirements, and return on investment will also need to be considered.
Over time, numerous models and decision support systems to guide the management of soil acidity have been developed worldwide. However, the logic, simplicity, and robustness embedded in RothLime make this paper a classic paper for me.
