Spatial variability of cotton potassium nutrition in relation to soil cations in agricultural fields

The adequacy of potassium (K) in plants is influenced not only by the amount of extractable K in the soil, but also by the presence and balance of other essential cations such as magnesium (Mg) and calcium (Ca). However, Mg and Ca are often overlooked in soil fertility assessments. Therefore, this research aimed to investigate K availability in cotton-growing agricultural soils, examine potential K deficiencies induced by high Mg and Ca levels, and map their spatial distribution. The research was conducted in the Amik Plain of Hatay Province, located in the easternmost part of Türkiye’s Mediterranean region. Ammonium acetate extraction for soils and wet digestion for plant tissues were used to determine K, Ca, and Mg contents. Relationships between soil and plant parameters were analyzed using Pearson’s correlation, while spatial trends of potassium deficiency linked to high Ca and Mg were modeled through Kriging interpolation. The results revealed that soil Ca and Mg levels were considerably higher than K, which adversely affected plant K uptake. K/Mg and K/Ca ratios in soil were found to range between 0.04–1.02 and 0.02–0.14, respectively. Leaf K concentrations varied between 0.47% and 3.25%, indicating widespread K deficiency. Contrary to the common assumption that soils rich in K do not cause deficiency, the findings showed that 57.1% of cotton plants grown in K-rich soils exhibited hidden K deficiency. Therefore, K/Ca, K/Mg, and K/(Ca+Mg) ratios should be considered when evaluating K availability in soils with high extractable K.