The state of soil organic carbon in agricultural lands of Iran with different agroecological conditions

Abstract

ABSTRACT Soil organic carbon (SOC), is one of the most important parameters determining soil quality and fertility, crop productivity as well as soil resistance to drought. Therefore, the preparation of accurate maps of SOC is of great importance not only for precision agriculture but also for selection of suitable strategies by policy makers. Iran suffers from deficiency of a comprehensive dataset of SOC in agricultural lands. Therefore, this study aimed to present the SOC map of Iran´s agricultural soils, to compare SOC content of different agricultural land use and to compare SOC of agricultural lands in different Iran´s agro-ecological zones (AEZs). For this purpose, 3327 sites were sampled. These sampling sites were located in different Iran´s agricultural land use types (irrigated agricultural lands (AgI), dry farming (AgD), horticultural (Ho) and fallow (Fa) lands) of Iran´s AEZs, which were selected based on soil and geology maps as well as using a 6000 × 6000 m grid-sampling pattern. According to SOC map of Iran, only 4% of all agricultural lands of Iran (0–30 cm) possessed >2% SOC. This area is located in AEZ2 with wet and humid conditions and expanse covers the western coast of the Caspian Sea. The SOC content in 70% of Iran´s agricultural topsoil is less than 1%. Meanwhile, about 10% of the topsoil ´agriculturallands had SOC more than 1.5%. In addition, among different studied land uses, SOC content of surface soil decreases as this trend Ho>AgI> AgD> Fa because of more SOC accumulation in horticultural and irrigated agricultural lands than dry farming and fallow ones. In addition, more dairy manure applied in the horticultural lands. According to the results of SOC map, it is essential to manage agricultural strategies for better SOC sequestration in different AEZs in order to achieve sustainable agriculture.