This article is concerned with soil-sustainability problems of agriculture in developing countries, in particular with soil erosion. The aim of our study is to develop a comprehensive model that explains the adoption of sustainable agricultural practices with respect to soil conservation. Our approach includes the following special features: (A) The model is comprehensive in that it includes a large number of institutional, personal–social, economic, and physical explanatory variables. (B) Particular attention is paid to the influence of marketing systems on the adoption of sustainable agricultural practices, which to our knowledge has been neglected in past research. (C) The concept of adopting sustainable agricultural practices (ASAP) is differentiated into a limited number of basic components of soil conservation.(D) The model is estimated by Principal Component Regression, which enhances efficient estimation of the impact of many explanatory variables on ASAP. Our model is applied to Cabuyal hillside farming in Colombia. The application demonstrates the usefulness of the proposed model. ASAP is differentiated into three basic components: soil-disturbance control, soil-protection practices, and run-off control. It appears that soil-disturbance control is particularly influenced by farmers’ characteristics, such as education and managerial variables. The second component, soil-protection practices, appears to be strongly influenced not only by farmers’ managerial variables but also by their relationship with their environment, in particular marketing institutions. The third soil-conservation component, run-off control, is influenced by the physical characteristics of the plot and by the available farm labor. Our empirical results demonstrate the usefulness of the proposed model in designing agricultural policies, because it can determine which variables are more likely to influence the adoption of a specific type of soil conservation.