Impact of Bentonite Application Methods, Timing, and Dosages on Field Emergence, Biomass Accumulation, and Photosynthetic Efficiency in Soybean (Glycine Max (L.) Merr.)

This paper reports findings from a multi-year agronomic trial (2024–2026) conducted in the Kashkadarya Region of Uzbekistan to evaluate how natural bentonite clay amendments (ranging from 100 to 750 kg/ha)—incorporated at seeding, or top-dressed during the floral budding and full bloom stages over a basal N90P60K90 fertilizer regime—govern seedling emergence, stand establishment, aboveground dry biomass dynamics, and net assimilation rate (NAR) in the soybean cultivar "Uzbek-6". Soil incorporation of 400–750 kg/ha of bentonite at seeding elevated field germination from 84.1% to 86.9–87.2% and enhanced pre-harvest plant population density by 5.9–6.8% relative to the unamended NPK control. Peak dry biomass yield at physiological maturity (72.3–72.6 dt/ha, compared to 65.5 dt/ha in the control) was achieved either through a three-way split application of 250 kg/ha each (at seeding, budding, and flowering) or via a 500 kg/ha split dressing divided equally between budding and flowering. Regression modeling demonstrated that every 100 kg/ha increment of bentonite generated a linear dry biomass gain of 1.20 dt/ha when supplied during reproductive development (budding and flowering) versus 0.75 dt/ha when applied solely at seeding.