Effects of potassium applications on wheat nutrition in calcareous and serpentine-derived soils

Potassium (K) is an essential macronutrient involved in numerous physiological processes in plants, including enzyme activation, osmotic regulation, and photosynthesis. However, its uptake is strongly influenced by soil properties and interactions among exchangeable cations. This study was conducted to investigate the effects of increasing K application rates on calcium (Ca), magnesium (Mg), and K uptake by wheat (Triticum aestivum L., cv. Esperia) grown in serpentine-derived and calcareous soils. The greenhouse experiment was conducted using a completely randomized factorial design. Plastic pots containing 2 kg of soil received K at 0, 50, 100, or 200 mg kg⁻¹, and the plants were harvested after 10 weeks. K application significantly increased plant K concentration from 1.03% to 1.33% and total K uptake from 51.32 to 72.64 mg pot⁻¹. Plant Ca concentration was not significantly affected, whereas plant Mg concentration decreased from 0.46% to 0.36%. Pearson correlation analysis revealed soil-specific relationships between plant growth and cation nutrition. In the serpentine-derived soil, dry matter (DM) production was strongly correlated with total K uptake (r = 0.8540). Plant K concentration was positively correlated with K uptake (r = 0.9823) but negatively correlated with plant Ca (r = −0.7022) and Mg concentrations (r = −0.6597). Soil K concentration was also negatively associated with plant Mg concentration (r = −0.7274). In the calcareous soil, DM production was positively correlated with soil K concentration (r = 0.6202) and total K uptake (r = 0.8452). A strong positive relationship was found between plant K concentration and K uptake (r = 0.9120), whereas plant K and Mg concentrations were negatively correlated (r = −0.7214). Overall, K fertilization promoted K accumulation and supported wheat growth, while its relationships with plant Ca and Mg differed between the two soil types. These contrasting patterns indicate that wheat responses to K application are influenced by the Ca-dominated environment of calcareous soil and the Mg-rich environment of serpentine-derived soil. Accordingly, soil characteristics and associated changes in Ca and Mg concentrations and uptake should be considered when evaluating K fertilization practices.