Soil fertility is one of many factors influencing farmers’ choices regarding agricultural production, fertilisation and soil and water conservation. However, before we can study the effects of soil fertility, we need to measure it. We use the QUEFTS model (Quantitative Evaluation of the Fertility of Tropical Soils Janssen et al, 1990) which predicts crop yields from chemical soil characteristics, as an indicator of soil fertility. We then compare these predictions with actual yields as well as farmers’ own estimates of soil fertility