Establishment of soil fertility indices of lower seyhan plain-sub irrigation area soils and determination of nutrient content at local scale

Understanding the physical and chemical properties of soils is essential for sustainable soil management, as relying on only a few parameters is insufficient due to the complex interactions both positive and negative among soil properties and nutrient elements. This study aimed to determine the spatial distribution of nutrient elements and to develop soil fertility indices in the Lower Seyhan Plain–Sub Irrigation Area, a subregion of the Çukurova Plain, one of Turkey's most fertile agricultural area. A total of 170 surface soil samples were randomly collected from agricultural fields and georeferenced using Geographic Information Systems (GIS). Soil analyses were evaluated spatially using ArcGIS 10.4 software, and thematic distribution maps were produced. Based on the Parker Nutrient Index, index scores and fertility maps were generated for various soil properties including texture, pH, electrical conductivity (EC), organic matter, CaCO3 content, mineral nitrogen (Nmin), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu). Results indicated that Nmin, available P, Zn, and Mn levels were generally low, while K, Ca, Mg, Fe, and Cu were found to be high. Spatial distribution maps highlighted the need to revise fertilization strategies, particularly in areas where nutrient levels were excessive. Comparisons by land use type revealed variations in nutrient status; notably, orchard soils exhibited higher Nmin, P, and Cu levels, suggesting that fertilization practices vary by land use. The generated fertility and nutrient maps provide a valuable decision-support tool for soil management, fertilization planning, and the implementation of sustainable agriculture practices.