Correlation between Leaf Area Formation and Net Photosynthetic Productivity in Soybean Varieties Under the Agroecological Conditions of Uzbekistan

Net photosynthetic productivity (NPP) is an important physiological indicator that characterizes the efficiency of plant photosynthesis and reflects the amount of dry matter accumulated by a plant per unit of leaf area during a specific period. It is closely associated with the intensity of carbon dioxide assimilation, the formation of organic compounds, and the accumulation of biomass through photosynthetic processes. The application of the highest nutrient rate played a decisive role in maximizing the assimilatory (leaf) area of soybean plants. The high mineral fertilizer rate (N₁₂₀P₉₀K₆₀) markedly increased leaf area, it was associated with a slight reduction in net photosynthetic productivity during the flowering-pod-setting stage. This response may be attributed to the excessive development and density of the stem-leaf canopy, which can increase mutual shading among leaves and consequently reduce the efficiency of light interception and photosynthetic assimilation within the canopy. In contrast, foliar application of Kalifos and SAKO under a moderate N₆₀P₄₅K₃₀ fertilization regime resulted in the highest net photosynthetic productivity during the budding flowering stage. Compared with the control, this treatment increased net photosynthetic productivity by 5.47-5.57 g/m² per day in the “Toshkent” cultivar and by 5.17-5.37 g/m² per day in the “Madad” cultivar.