Soil salinity variation in a coastal. A study was undertaken during one year in a sandy soil of the mediterranean coast, in stands colonised by trees Pinus pinea (L) stand. Clear differences were observed in the salinity content of the two sites : it is much lower under the grass site than the forest site, except for the surface layer. These differences could be attributed to biotic and climatic factors.The data indicated also that the seasonal évolution of total salinity and the concentration of the majors ions : Na, K, Ca, Mg and Cl is very correlated with climatic factors such as precipitation and evaporation. The highest values are observed in July and August, during the dry season, the lowest in winter, after the rains of the autumn. Regarding chloride concentration, the maximum observed during the dry months was nearly 2 g l-1 This value allow to use a neutron moisture probe for measuring the soil water in this site.