Vol. 7, Issue 10, Part G (2025)

A field experiment was conducted at the Department of Agronomy, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani, Maharashtra, during the kharif season of 2024 to investigate crop coefficient, growing degree days (GDD), photo-thermal units (PTU), and helio-thermal units (HTU) for soybean (Glycine max [L.] Merrill). The experiment followed a split-plot design with three replications and included two factors: three sowing dates D₁ (SMW 25), D₂ (SMW 26), and D₃ (SMW 27) and four soybean varieties: V₁ (JS 93-05), V₂ (MAUS 612), V₃ (MAUS 725), and V₄ (MAUS 731). Each treatment was sown with a spacing of 45 × 5 cm, total 12 treatments across 36 plots. The gross layout measured 5.4 × 4.5 m, with each net plot sized at 4.5 × 4.1 m. The study aimed to determine the duration of phenological stages, quantify thermal requirements, and assess the application of thermal indices in predicting soybean development. Results revealed that the highest accumulation of GDD (2569.6 °C days), HTU (11303.6 °C days hrs.), and PTU (20157.0 °C days hrs.) was observed under D₂ (SMW 26). In contrast, the lowest values were recorded under D₃ (SMW 27), with GDD at 2299.2 °C days, HTU at 9024.9 °C days hrs., and PTU at 18125.8 °C days hrs.