VALORISATION DES MARGINES POUR AMELIORER LA QUALITE DES SOLS DANS LES ZONES ARIDES TUNISIENNES

Abstract

Soils of arid regions are relatively poor in organic matter. This depletion is accelerated by crop intensification, the light texture of the soil and the non return of crop residues in the soil. Thus, the depletion of organic matter in these soils increases the degradation and depletion of soil fertility and promotes erosion and desertification processes. To preserve and maintain soil productivity, the contribution of organic amendments is essential. However, these improvements alterations are not always available and their quality is often poor and we use other sources of organic amendments. Among these amendments is oil mill wastewater (OMW) which may constitute a possible amendment to the poor soils of arid regions. As part of the agricultural use of OMW as fertilizer, we conducted a test application of OMW on the sandy soil of Medenine (southern Tunisia), not grown in pots in order to enhance the beneficial or negative effects of this effluent on chemical soil characteristics. The experiment was conducted in pots over 3 months. Three increasing doses of OMW (T50 = 50 m3 ha-1; T100 = 100 m3 ha-1 and T200 = 200 m3 ha-1) were applied and compared to an unfertilized control, with or without the application of fresh or salt water as irrigation. The rate of organic matter increased progressively with the increasing doses of oil mill wastewater (0.81%; 1.53% et 3.2% for the treated samples T50; T100 et T200) compared to the control (0.3%). Decreases in these rates were recorded over time. In addition, these two types of irrigation modify only slightly the contents of organic matter in soils. Concentrations of exchangeable potassium increased with the dose of applied OMW (50; 240 et 330 mg/kg for the treated samples50; 100 et 200 m3 ha-1) compared to the control (39 mg/kg). However, the application of irrigation did not affect the levels of this parameter, the pH of the treated samples remained unchanged, and the electrical conductivity of the soil did not increase at an alarming rate