We compare the effects of minimum and conventional tillage on banana growth, under irrigated and rain-fed conditions. Measurements of leaf growth, root length density and soil water depletion were made. We used a crop simulation model to understand and explain the differential behavior of banana plants in the experiments. Our approach consisted of (i) an adaptation of the STICS model, initially developed for temperate crops, to the banana crop grown under tropical conditions and (ii) use of the integrative ability of the model to identify the respective roles of irrigation and tillage. The adaptation of the model concerned the phasic development, and leaf and root growth. Some specific characteristics of the tropical environment were also introduced. The model points out that under irrigated conditions crop water requirements were always satisfied whatever the tillage depth. In that case, the difference in terms of leaf growth and yield between shallow and deep tillage treatments can be explained by the nitrogen deficit due to a poor root system. Rain-fed crops suffered from water shortage, but the increase in soil exploration, allowed by conventional tillage, compensated for the absence of irrigation. This work improves knowledge of the agro-physiology of the banana crop. It demonstrates the fundamental part played by the root system, which appears as an important limiting factor for a correct water and nutrient supply. It provides an opportunity to elaborate a global model for the banana crop.