Algeria has known both past decade a significant rainfall deficit and a poor distribution of rainfall in time and space of climate change. The stresses of climate, population growth and the reduction of agricultural land to urban planning have forced farmers to intensify their crop for their income. This indiscriminate intensification of agricultural activities (fertilizer, irrigation .....) led to the following water pollution by fertilizers and other chemicals. Pollutants cause environmental damage and threaten human health.
In the context of preserving the quality of these waters, this work aims to evaluate the impact of changing agricultural practices on water quality throughout the watershed of Sidi Rached by applying models Apex.
The data used are climatic (precipitation, temperature ....), a Digital Terrain Model, a soil map, a map of land use and agricultural practices from surveys.
The model provides a calibration Apex satisfactorily calibrated and validated hydrological conditions in the basin of Sidi Rached with an index of 0.6 Nash received over the period 2008-2009, the dynamic transfer of nitrate is also reproduced. Cultural practices affect irrigated crops studied most dominant in the study area namely vegetable crops and citrus, which comes in three scenarios: 1) - Nitrogen reduced (50% reduction in fertilizer usually applied) and 2) - Improved irrigation (control via software), 3) - reduced nitrogen fertilization and irrigation improved (combination of both scenarios).
The results show that this is the scenario 3, which reduces consistently the amount of nitrogen leached, while inducing a drop in yield limited.
These results may provide a basis for reflection on the subject and bring those responsible for facilities management of the area of Sidi Rached to perform tests similar to research and extend the best agricultural practices primarily related to irrigation and fertilization .
Keywords: agricultural practices, soil modeling, water quality, nitrate, fertilization, irrigation, Apex.