Yield Structure of Coloured Potato Cultivars Under Biostimulant Application Across Contrasting Growing Seasons

Potato yield structure is strongly influenced by climatic variability, which complicates agronomic recommendations for cultivars differing in flesh colour. A three-year field experiment evaluated associations between two foliar biostimulant treatments, GumiSil-C and Terra Sorb Complex ® , and yield structure in five potato cultivars under contrasting hydrothermal conditions. Growing season and cultivar significantly affected all yield traits, whereas treatment-associated responses were conditional. The highest total and marketable yields occurred in 2022, while the severe precipitation deficit in 2023 coincided with lower total, marketable, and large-tuber yields. Terra Sorb Complex ® was associated with the highest total, marketable-size, and marketable yields in 2022, whereas higher large-tuber yields were more frequently recorded following GumiSil-C application. Neither treatment was consistently associated with higher marketable yield across seasons. Significant three-way interactions for by-product yield and defective tuber mass indicated cultivar- and season-specific responses. Cultivar selection and adaptation to local hydrothermal conditions remained the principal determinants of commercially valuable yield.