Growth dynamics and physiological indices of Bt cotton as affected by controlled-release fertilizer levels under rainfed agriculture

A field investigation was carried out during the kharif seasons of 2022-23 and 2023-24 on clayey soils at the Department of Agronomy, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani, to evaluate the influence of controlled-release fertilizers (CRFs) on the growth and physiological performance of Bt cotton under rainfed conditions. The experiment was conducted in a randomized block design with eight treatments and three replications. The nutrient management treatments included: The treatments details consist of viz., T₁- Control, T₂- Recommended dose of fertilizer, T₃- Controlled release fertilizer @ 50 kg ha^-1, T₄- Controlled release fertilizer @ 100 kg ha^-1, T₅- Controlled release fertilizer @ 150 kg ha^-1, T₆- Controlled release fertilizer @ 200 kg ha^-1, T₇- Controlled release fertilizer @ 250 kg ha^-1 and T₈- Controlled release fertilizer @300 kg ha^-1. The study focused on quantifying key physiological growth indices such as Absolute Growth Rate (AGR), Relative Growth Rate (RGR), Crop Growth Rate (CGR), Net Assimilation Rate (NAR) and Leaf Area Index (LAI), which collectively determine biomass accumulation and crop productivity. The results indicated a progressive improvement in cotton growth parameters with increasing levels of CRF. Among the treatments, Controlled release fertilizer @ 300 kg ha^-1 (T₈) consistently recorded the highest AGR for plant height and total dry matter production, reflecting accelerated vegetative development. Mean values of RGR, CGR, NAR and LAI were also found to be maximum under T₈, suggesting enhanced assimilatory efficiency, sustained nutrient availability and efficient canopy development. The controlled and gradual nutrient release from CRF ensured optimal nutrient uptake during critical growth stages, thereby improving physiological processes essential for higher biomass production.