Calcium, Magnesium and Potassium Nutrition of Peanut as Influenced by Soil Cation Ratios

Calcareous soils derived from limestone and related parent materials are widespread in southern Türkiye, including the eastern Mediterranean region. These soils typically contain high levels of exchangeable calcium and, in many cases, substantial amounts of magnesium. In calcareous environments, nutrient behavior is strongly linked to cation proportions. Where calcium (Ca) is abundant, it may influence the relative availability of magnesium (Mg) and potassium (K) through exchange-related interactions. Therefore, concentration values alone may not fully represent plant-accessible nutrient status. For this reason, evaluating soil fertility solely on the basis of individual nutrient concentrations may overlook imbalances that affect plant nutrition. To address this issue under practical field conditions, we examined selected soil cation ratios and their relationships with Ca, Mg and K concentrations in peanut grown in the Osmaniye region, where calcareous soils are dominant.

Field sampling was carried out in peanut-growing areas of Osmaniye province. A total of 45 surface soil samples were collected, together with the youngest fully expanded peanut leaves at the full flowering stage. Soil samples were air-dried, sieved and characterized in terms of pH, electrical conductivity (EC), calcium carbonate content, organic matter and exchangeable Ca, Mg and K concentrations. Leaf samples were oven-dried, ground and subjected to wet digestion prior to determination of Ca, Mg and K using atomic absorption spectrophotometry (AAS). Base cation saturation ratios were derived from exchangeable cation data. The associations between soil properties and leaf nutrient concentrations were examined using correlation analysis and principal component analysis (PCA). Spatial variability of selected parameters was mapped by kriging interpolation within a GIS environment.

The study area is dominated by soils formed from the weathering of limestone and dolomite and this geological background is reflected in their chemical composition. Exchangeable Ca and Mg levels were consistently high, resulting in elevated Ca/K and Mg/K ratios across most of the sampling area and likely restricting K uptake, thereby causing K deficiency in peanut leaves. Both correlation analysis and principal component analysis (PCA) revealed clear antagonistic relationships between K and the divalent cations, whereas Ca and Mg tended to vary in the same direction. Spatial evaluation further showed that locations with higher soil Ca/K and Mg/K ratios frequently coincided with reduced foliar K levels. This pattern suggests that the dominance of Ca and Mg, largely controlled by parent material, may influence K nutrition in the region. Overall, the results support the consideration of cation balance, in addition to individual nutrient concentrations, when developing fertilization strategies for peanut production.