Seasonal Dynamics of Free Amino Acids and Mineral Elements in Cotton (CV. “ANDiJAN-36") and Identification of Critical Nutrition Stages

The efficiency of the cotton nutrition system is determined by its correspondence to the physiological needs of the plant at different stages of ontogenesis. This study investigated the seasonal dynamics of total nitrogen, free amino acids (FAA), macro- and microelements in the roots, stems, and leaves of cotton (variety “Andijan-36”) during key phenological phases: seedling, budding, flowering, boll formation, and maturation. Quantitative chemical analysis (Kjeldahl, HPLC, AAS) revealed clear phase-specific patterns of nutrient accumulation and remobilization. The maximum content of total nitrogen and key FAA (glutamine, asparagine) was observed during the budding phase, identifying it as critical for the formation of the photosynthetic apparatus and generative organs. The flowering phase was characterized by a peak in proline content, indicative of a stress response, and potassium, performing an osmoregulatory function, along with concentration maxima of the microelements Zn, Mn, Cu, and B, essential for enzymatic activity and fertilization processes. Based on the identified dynamics, critical consumption phases were established, and a strategy for the precision application of liquid nitrogen fertilizers based on a Urea-ammonium nitrate (UAN) solution, modified with amino acids (glycine, alanine, valine) and microelements, was developed. Implementation of the proposed technology, as calculations show, could increase cotton yield by 10–12%, improve fiber quality, increase the nitrogen use efficiency (NUE) by 15–20%, and enhance plant stress tolerance.