Nitrogen plays a key role in the fertility of agricultural land. However, its management requires an understanding of its dynamics in the soil. In this perspective, our research aims at characterizing and distributing nitrogen in the different granulometric and organic fractions of some Tunisian soils. The majority of crops also need small amounts of trace elements. The lack of these micronutrients, for example boron, will result in detrimental symptoms. It should also be noted that its content depends on the properties of the soil. It is in this context that the second part of this work on the distribution of boron in the different granulometric fractions and the understanding of the mechanisms that manage its availability in the soil. Irrigation with poor quality water can have dramatic consequences on soils. The reuse of treated wastewater (TWA) can be one of the solutions. However, this water can be a source of pollution. In this context, the last part of our research on the effects of TME irrigation on soil properties is included.