Evaluation of soil fertility in northwest Iran: A comparison based on elevation

Abstract

Abstract Soil fertility and nutrient management are the main factors that directly affect the yield of the product. To evaluate the soil fertility at different elevations (including 1600-2000, 2000-2400, 2400-2800, and >2800 m), 350 surface soil samples (0-30 cm) were collected from the agricultural lands of northwestern Iran. Then, soil properties, including soil texture (%), CaCO3 (%), pH, EC (dS.m-1), organic matter (OM) (%), and soil nutrients (macro and micro) (mg.kg-1), were measured. Finally, the interpretation and classification of the soil samples were made using the nutritional value index (NIV) based on the Gomez and Common methods. The comparison of the NIV index based on elevation changes showed that the Gomez method tends to classify the soil properties in the optimal class due to its tendency towards the center of the data. But the Common method is more consistent with reality. After classifying the NIV index using the Common method, it was determined that CaCO3 (%) and soil salinity is not the main problem for soil fertility in different elevation classes. However, in all elevations, high pH, low OM (%) at elevations >2800 m, total nitrogen (TN) (mg.kg-1), available phosphorous (AP) (mg.kg-1), and micronutrients deficiencies (except Zn at the elevation of 1600-2000 m) are the main limiting factors for soil fertility of agricultural lands. Therefore, to improve the soil fertility in all the elevations of the agricultural lands in the northwest of Iran, there is a need to improve the condition of macro and micronutrients (mg.kg-1), especially TN (mg.kg-1).