MODULATION OF VEGETATIVE GROWTH, SYMBIOTIC NODULATION, SEED YIELD, AND BIOCHEMICAL QUALITY OF SOYBEAN (GLYCINE MAX (L.) MERR.) BY BENTONITE PLACEMENT STRATEGIES, PHENOLOGICAL TIMING, AND APPLICATION RATES

A three-year field investigation (2024–2026) was conducted on irrigated light serozem soils in the Kashkadarya Region of Uzbekistan to evaluate how natural bentonite clay amendments (100–750 kg/ha)—supplied via distinct placement methods and phenological schedules against a basal N90P60K90 fertilization background—affect crop establishment, canopy development, root nodulation, yield architecture, and seed nutritional composition in the commercial soybean cultivar "Uzbek-6". Incorporating bentonite enhanced field seedling emergence from 84.1% to 87.2%, expanded pre-harvest plant population density by 1.0–6.8%, boosted three-year mean seed yield from 31.7 to 32.1–36.3 dt/ha (an increment of 0.4–4.6 dt/ha, or 3.17 to 3.21–3.63 t/ha), and elevated crude seed protein concentration up to 39.4%. Regression and correlation modeling revealed that seed yield responded linearly to total bentonite dosage (r = 0.989) and was governed primarily by seasonal plant survival rate (r = 0.901) and individual plant seed productivity (r = 0.869).