Heat unit requirements for growth and development of safflower (Carthamus tinctorius L.) varieties under different growing environments

Abstract

A field experiment was conducted during rabi season 2024–25 at the Research and Instructional Farm of Indira Gandhi Krishi Vishwavidyalaya (IGKV), Raipur, Chhattisgarh, to studies on response of safflower cultivars under different growing environments. The experiment comprised three dates of sowing viz., D1(3rd Dec), D2(13th Dec) and D3(23rd Dec) and three safflower varieties namely CG Kusum-1, IGKV Kusum, and CG Kusum-2. Accumulated Growing Degree Days (AGDD), Accumulated Photo Thermal Units (APTU) and Accumulated Helio Thermal Units (AHTU) increased progressively from emergence to physiological maturity in all treatments. Maximum heat accumulation °Ccurred under D1 (3 Dec), followed by D2 (13 Dec) and D3 (23 Dec). At physiological maturity, AGDD ranged from 2871.5 to 2964.7°C days in D1, 2694.8 to 2780.3°C days in D2 and 2535.6 to 2616.7°C days in D3. Among varieties, IGKV Kusum accumulated the highest thermal units followed by CG Kusum-1 and CG Kusum-2. Heat Use Efficiency (HUE) and Radiation Use Efficiency (RUE) were highest under D3, indicating more efficient utilization of available heat and radiation at delayed planting. CG Kusum-1 exhibited the highest HUE (0.80 g m⁻² °C Day⁻¹) and RUE (1.47 g m⁻² MJ⁻¹).