Farmers are increasingly required to justify their practices and to change their technical management approach due to the development of integrated production, new regulations and private standards. The feasibility of these changes can be assessed by analysing the practices of farmers. Here, we analysed the practices of farmers in apple orchards in the Mauguio-Lunel plain, France from an agronomic viewpoint, focusing on irrigation and N fertilizer. Our study was based on interviewing farmers about their practices and factors that influence their decisions. Interviews were supported by model-generated irrigation and fertilizer application schedules related to the considered plots. Fertilizer data recorded over a two-year period (2002 and 2003) were compared to data from interviews. Our results show that (1) irrigation practices were highly dependent on pest control practices; (2) chemical spraying against the codling moth [Cydia pomonella] strongly influenced irrigation frequency; (3) irrigation practices were dependent on irrigation devices; and (4) fertilizer application practices were highly dependent on the conceptions that farmers had about the role of N fertilizers. These conceptions were associated with timing, fertilizer formula and modulation rules. Based on data recorded by farmers over a two-year period, fertilizer application practices were highly variable. Likewise, these data also differed from data collected during interviews. Overall, our findings underline the importance of considering interactions between cultural practices and farmers' conceptions to understand farmers' practices. It also stressed the need to consider data recorded by the farmers themselves only as a partial source of information and to design better interviewing procedures with farmers.