overview of agricultural soil fertility status of iran

this study was carried out in order to develop a soil fertility database and to assess agricultural soil fertility of country. to this end, 315000 soil test data (more than 50000 soil samples) that provided by laboratories of soil and water research centers in 30 provinces of iran between 2002 and 2012 was collected. results revealed that amount of  plant available  phosphorus and potassium of  71.8% and 21.0% of  agricultural soils  are less than critical levels of these two elements( p=15 , k= 180 mg kg-1) respectively. organic carbon content of 63.2 % of collected soil samples was  less than 1%  which shows poor organic matter status of agricultural soils of country. the results also showed that among the micronutrients, zinc and iron were the most commonly deficient in agricultural soils in which   56% and 40% of soil samples were  below the 0.75 mg kg-1 zinc and 4.5 mg kg-1 iron respectively. moreover,  87% of  collected soil samples have more than 5% calcium carbonate equivalent which means majority of  agricultural soils of iran are affected by calcium carbonate. in addition, 80% of soils have ph levels between 7.5 and 8.5 and 95% of them are alkaline (ph>7). the majority of soil texture classes were loam (21%) and clay loam (16%).