Potassium Efficiency in Soybean: Assessing Split Fertization Strategies and Soil Texture Effects on Physiology and Yield

Soybean (Glycine max (L.) Merrill) physiology and yield are highly dependent on potassium (K) availability, a nutrient that plays a pivotal role in plant metabolic processes. This study investigated the physiological responses and agronomic performance of soybean subjected to various K split-application strategies across contrasting soil textures (clayey and sandy) in two independent field experiments. Treatments consisted of a K rate of 90 kg ha−1 K2O (applied as KCl) allocated either as a single application or in split combinations across different developmental stages: pre-sowing (PS), sowing (S), vegetative (V4), and reproductive (R1), alongside an unfertilized control. A randomized complete block design with four replicates was used. Physiological traits (chlorophyll and carotenoid contents, and gas exchange parameters), biometric attributes, and yield components were evaluated. In sandy soil, applying 100% of the K rate at PS ensured early nutrient availability, enhanced photosynthetic performance, and maximized soybean grain yield. Conversely, in clayey soil, a full application at sowing and the split strategy (75% S + 25% V4) demonstrated equal efficacy, offering viable and flexible options for K management. These findings demonstrate that K fertilization strategies must be tailored to soil texture to optimize soybean physiology and maximize agronomic efficiency.