Cengiz Kaya¹, Osman Sonmez², Salih Aydemir² and Ali Volkan bilgili³, (1)Harran University, Department of Soil Science and Plant Nutrition,  Sanliurfa, Turkey, (2)Department of Soil Science and Plant Nutrition, Harran University, Sanliurfa, Turkey, (3)Department of Soil Science and Plant Nutrition, Harran University, sanliurfa, Turkey

Calcareous soils reduce the nutrient availability in agricultural production over 600 million ha of cultivable soils worldwide. Two of the most key factors that limit agricultural production in these types of soils are reduced solubility of phosphorus and high pH. The calcareous soils in arid and semi arid regions are also naturally low in organic matter because of high temperature. The aim of the study was to test the effects of some organic such as leonardite and liquid humic acid and the inorganic substances such as sulfur on the soil pH and phosphorus fixation. An incubation study was designed in glasshouse conditions. Two levels of P (0 or 50 mg/kg) were combined with different levels of leonardite, liquid humic acid and sulfur and incubated for 90 days. The results indicate that especially, using organic and inorganic substances in combination reduced soil pH in both main P treatments and also reduced phosphorus fixation in 50 mg P/kg treatment.