Water is becoming a scarce and expensive commodity, allowing to irrigate limited areas. Irrigation is poorly managed and this situation allow salts accumulation and soil degradation. The rainwater retained by soil is important and must be studied, first by its volume and thereafter by its fluctuations over time. The actual soil volume exploited by roots, viable and economic plant species that would be able to value such water potential should also be evaluated. The principal constraint to solve for development of these soils would be maintaining an adequate water supply of crops. The present paper aims to evaluate the means and measures necessary to manage this water rationally. During one year (2007-2008), we investigated soil water reserve in each field (Rapeseed, fallow). The water profile analysis showed that fallow lose more water than cultivated soil over this period. The understanding of water flux through the soil, and its relationship with the plant-atmosphere may be also used for the optimization of rainwater.

Keywords: Rainwater, soil properties, Plant species, Water profile, Water reserve