Soil characteristics of study field
Descriptive analysis of selected soil properties revealed that soil pH values varied from slightly alkaline to moderately alkaline (Table 1). According to the salinity criteria of
Maas (1986), electrical conductivity values classified the soils as non-saline. Calcium carbonate contents varied widely, with a mean value of 22.61%. The average soil organic matter level was evaluated as moderate according to
Ülgen and Yurtsever (1974).
Concentrations of exchangeable cations
Exchangeable cation concentrations in soils from the study area varied considerably, with mean concentrations of Ca (Ca-s), Mg (Mg-s) and K (K-s) of 8236, 1473 and 532 mg kg
-1, respectively (Table 2).
Base cation saturation ratios (BCSR) of the soils
Elemental analyses of soil samples indicated that Ca/K ratios ranged from 7.8 to 152, with a mean value of 38.5, while Ca/Mg ratios varied between 0.3 and 11.4, averaging 4.56. In addition, Mg/K ratios ranged from 1.9 to 64.6, with a mean value of 3.18 (Table 3).
Foliar concentrations of Ca, Mg and K
Foliar analyses of peanut plants revealed that Ca (Ca-p) concentrations ranged from 0.82 to 3.52%, with a mean value of 1.62%, while Mg (Mg-p) concentrations varied between 0.64 and 1.78%, averaging 1.29%. Potassium (K-p) concentrations ranged from 0.54 to 1.73%, with a mean of 0.98% (Table 4).
Effect of base soil cation ratios (BCSR) on plant nutrients
The distribution matrices of Ca-s, Mg-s and K-s concentrations and the Ca/K, Mg/K and Ca/Mg ratios in the soils of the Osmaniye region revealed a significant negative correlation between exchangeable soil Ca and K (p<0.01; r = -0.23). Additionally, the soil Ca/K and Mg/K ratios exhibited significant negative correlations with exchangeable soil K, with correlation coefficients of -0.13 and -0.76, respectively (p<0.01). Regarding plant tissue concentrations of the examined elements, plant K-p exhibited significant negative correlations with both Ca-p and Mg-p (p<0.01; r = -0.15 and p<0.01; r = -0.59, respectively). In contrast, a significant positive correlation was determined between plant Ca-p and Mg-p (p<0.01; r = 0.16) (Fig 2).
Principal component analysis of the variables
Principal component analysis (PCA) performed on the cation ratios derived from available Ca, Mg and K contents of the soils collected from the Osmaniye region, along with leaf concentration data, identified three principal components with eigenvalues greater than 1. In each PCA component, variables exhibiting the highest loading values were considered representative of the cation ratios and plant concentrations. The loadings (weights) of soil and plant parameters associated with each principal component are presented in Table 5. Based on the loading criteria, the variable exhibiting the highest absolute loading value, together with other variables within approximately 10% of this value, was considered in the selection process
(Andrews et al., 2002). Among the six principal components, PC1, PC2 and PC3, with eigenvalues of 2.53, 1.39 and 1.04, respectively, were selected. These principal components explained 42.274%, 23.230% and 17.482% of the total variance, respectively, accounting for a cumulative explained variance of 82.985% (Table 5). The eigenvectors associated with the three principal components with eigenvalues greater than 1, which cumulatively explained 82.98% of the total variance of the parameters, are presented in the table below. In PC1, Mg-p and K-p exhibited the highest loadings, indicating a strong contribution of these variables to this component. For PC2, Ca-p and Mg-p, together with the Ca/K and Mg/K ratios, showed high loadings and were identified as the main contributing variables. In PC3, Ca-p and the Ca/K and Ca/Mg ratios had the highest loadings and were the principal contributors to this component.
Based on the above-mentioned eigenvector values, examination of the three-dimensional (3D) representation of the principal components revealed contrasting directional patterns between plant K (K-p) concentrations and those of Ca-p and Mg-p. As indicated in the eigenvector matrix, K-p exhibited negative loadings in PC1, whereas Ca-p and Mg-p were positively loaded. Similarly, in PC2, Ca-p and Mg-p showed negative loadings, while K-p was positively loaded. Taken together, plant Ca and Mg exhibited similar loading directions, in contrast to plant K, which exhibited an opposite trend. Consistent patterns were also observed in the 3D distribution matrix of these variables, reflecting their three-dimensional spatial relationships (Fig 3).
Spatial distribution model analysis of the study area
The exchangeable soil K concentration, soil Ca/Mg ratio and plant K concentration reported in Table 6 were based on normally distributed data. However, as the data for available soil Ca and Mg concentrations, soil Ca/K and Mg/K ratios and plant Ca and Mg concentrations did not meet the normality assumption, appropriate data transformations were applied and the transformed values are presented in the table.
Spatial distribution maps illustrating soil Ca, Mg and K concentrations, the Ca/Mg, Ca/K and Mg/K ratios, as well as the concentrations of these elements in peanut plants cultivated in the soils of the Osmaniye region, are presented in Fig 4. As depicted in these maps, soil Ca concentrations were consistently high across the entire study area, with markedly elevated levels recorded in the northern part of the region (Fig 4a). Soil Mg concentrations exceeded 1500 mg kg
-1 in more than half of both the northern and southern sections of the study area (Fig 4b). Soil K concentrations were relatively high in more than half of the study area and no signs of potassium deficiency were observed in the regional soils (Fig 4c). Across the plain, soil Ca/Mg ratios ranged between 6.6 and 11.2 (Fig 4d). The Ca/K ratio varied considerably, with values between 19.06 and 29.9 in some parts of the plain and higher values reaching 30 to 73.3 in others (Fig 4e). A similar spatial pattern was observed for the Mg/K ratio. Lower values (2.7-11.2) were mainly observed in the eastern and northern parts of the plain, whereas higher ratios (11.3-46.8) occurred in the southern and western areas (Fig 4f).
The spatial maps indicate that Ca concentrations in peanut leaves were above 1.26% across most of the study area (Fig 5a). K concentrations ranged from 1.20 to 1.25% in the southern and western parts of the region, with higher values (>1.33%) in the north (Fig 5b). Conversely, plant Mg concentrations exhibited a distinct spatial pattern, with lower values (0.7-0.8%) predominating in the northern areas and higher concentrations (0.9-1.3%) observed in the central and southern regions (Fig 5c).
A detailed assessment of the characteristic properties of the regional soils indicated that they predominantly exhibited slightly to moderately alkaline reactions, together with relatively high lime contents (Table 1). In accordance with the classification proposed by
Rehm et al., (1996), nearly all soils in the study area were found to contain sufficient levels of potassium (Table 2). Based on the mean concentrations of Ca and Mg in the study area (Table 2), excessively high levels were identified over wide spatial extents of the region, as illustrated in Fig 4a-4b.
Kalkancı et al. (2021) reported that the soils of the Osmaniye region are predominantly highly calcareous and contain high levels of plant-available calcium (Ca) and magnesium (Mg). The Osmaniye region is characterized by extensive agricultural lands developed on diverse parent materials, including basalt, basaltic tuff, marl, alluvial and colluvial deposits, limestone, ophiolite and serpentinite
(Şimşek et al., 2021). Koca (2000) also documented that the study area, located in the northern segment of the Amanos orogenic belt, is underlain by formations composed of interbedded Devonian-aged dolomitic limestone, shale, dolomitic breccia and sandstone. As inferred from the regional geology, the elevated levels of plant-available calcium (Ca) and magnesium (Mg) in the soils are largely attributable to the mineralogical composition of the parent materials from which these soils have developed.
Evaluation of soil analyses and plant-available nutrient concentrations indicated that the Ca/K and Mg/K ratios in the soils of the study area were, on average, substantially higher than the proposed ideal cation ratios (Table 3). Additionally, the soil Ca/Mg ratio was comparatively closer to the ideal range, with a mean value of 4.56, relative to the other cation ratios (Table 3). The ideal cation ratios for Ca/K, Mg/K and Ca/Mg have been reported as 13, 2 and 6.5, respectively (
Chaganti and Culman, 2017).
Zalewska et al., (2018) reported that balanced mineral composition and suitable cation ratios were linked to higher yields. Potassium saturation above 5% was associated with increased yield, whereas excessive K accumulation reduced Mg and Ca concentrations and impaired forage quality. When K saturation declined below 4%, yield decreased in annual grass. The elevated soil Ca/K and Mg/K ratios observed here indicate a potential cation imbalance that may restrict optimal K nutrition. Attention to cation ratios may therefore help sustain yield and quality in the region.
Peanut leaves exhibited mean Ca, Mg and K concentrations of 1.62%, 1.29% and 0.98%, respectively. Reference thresholds reported by
Jones et al., (1991) indicate that adequate foliar status is associated with K, Ca and Mg concentrations above 1.7%, 1.25% and 0.30%. A significant negative relationship was observed between Ca and K in plant tissues. Magnesium also showed a strong negative association with K (Fig 2). These results point to potential antagonistic interactions affecting K uptake. PCA results were consistent with these patterns. Plant Mg contributed positively to PC1, while plant K loaded negatively. In PC2, plant Ca and Mg were negatively associated, whereas plant K showed a positive loading, together with soil Ca/K and Mg/K ratios (Table 6). The 3D PCA score plot further reflects the contrasting responses of K relative to Ca and Mg (Fig 3).
Spatial distribution maps indicate a close association between soil cation balance and peanut nutrient patterns in the Osmaniye Plain (Fig 4-5). High soil Ca levels across much of the study area, particularly in the northern part, are consistent with carbonate-rich lithology and ongoing calcification processes. Likewise, Mg concentrations exceeding 1500 mg kg-1 reflect the presence of dolomitic limestone and serpentine parent materials, contributing to Ca-Mg enrichment at the landscape scale. Although soil K concentrations were generally within adequate ranges, Ca/K and Mg/K ratios exceeded recommended thresholds in several parts of the plain, especially in the northern and eastern areas. Under these conditions, potassium availability appears to be influenced more by cation imbalance than by absolute soil K levels. Plant nutrient maps further show lower foliar K concentrations in locations characterized by elevated soil Ca/K and Mg/K ratios, whereas foliar Ca and Mg levels were comparatively high. These spatial trends align with the negative correlations observed in the statistical analyses and support the presence of antagonistic interactions among Ca, Mg and K. At the regional scale, K limitation therefore seems to be associated primarily with cation balance rather than with an overall shortage of soil K. From a management perspective, reliance on soil K concentrations alone may not adequately reflect nutritional constraints in peanut production. Incorporating Ca/K and Mg/K ratios into fertilization planning, particularly in calcareous environments, may provide a more reliable basis for nutrient management decisions. Nutrient interactions in soil–plant systems are complex and may shift between synergistic and antagonistic responses depending on environmental conditions (
Fageria, 2001). Elevated Ca and Mg concentrations can intensify ionic competition at exchange sites and reduce K uptake (
Hannan, 2011;
Wacal et al., 2019). For instance,
Pegues et al., (2019) reported a negative relationship between plant Ca and K following gypsum application. Similarly,
Demir and Dikici (2025) observed excessive Mg accumulation and reduced K concentrations in plants grown on serpentine soils with high Mg/K ratios.
Xie et al., (2021) further emphasized the importance of maintaining K+-Mg²+ balance, noting that imbalances in soil K/Mg ratios can restrict plant growth across species.
Potassium is fundamental to several physiological processes in plants, including stomatal regulation, nutrient transport and protein synthesis. In peanut, adequate K nutrition is associated with improvements in kernel size, test weight and overall yield performance
(Nagaraju et al., 2024). Previous research on legumes similarly demonstrates that potassium plays a pivotal role in regulating nutrient uptake and sustaining plant productivity. Potassium application has been shown to enhance growth, yield and nutrient acquisition in legume-based systems, including groundnut and lentil
(Reddy et al., 2023; Singh et al., 2026). Furthermore, potassium-mediated mechanisms have been reported to improve plant performance under stress conditions, particularly in black gram
(Ahmad et al., 2025). In addition, improved nutrient management practices have been shown to increase nutrient uptake efficiency and crop productivity in legume systems
(Balasubramanian et al., 2024). Therefore, maintaining a balanced K status in the soil-plant system is critical for optimizing nutrient interactions under varying environmental conditions. Nutrient uptake reflects complex interactions among elements, which may be neutral, synergistic, or antagonistic
(Rietra et al., 2017). In the Osmaniye Plain, elevated Ca and Mg concentrations contributed to increased Ca/K and Mg/K ratios. Although soil K levels were generally sufficient, these imbalances were associated with comparatively low foliar K concentrations. Fertilization strategies should therefore account for cation balance in addition to soil K concentration. Where soil conditions limit nutrient transfer to plants, foliar K application may serve as a complementary approach. Direct foliar application can help reduce soil-induced antagonistic effects and mitigate K deficiency (
Mikkelsen, 2017).
