Phenology and Heat Unit Requirement of Wheat Varieties under Different Thermal Environments and IW: CPE Ratio-Based Irrigation Scheduling

A field experiment was conducted during rabi seasons of 2020-21 and 2021-2022 to study the heat unit indices viz; accumulated growing degree days (GDD), helio-thermal unit (HTU), photo-thermal unit (PTU), phenothermal index, helio-thermal use efficiency (HTUE), photothermal use efficiency (PTUE) and heat use efficiencies (HUE) at different phenological stages of two wheat (Triticum aestivum L.) varieties (Lok 1 and MP 3336) grown under different thermal environments (3rd December, 18th December and 2nd January) and irrigation schedules (IW: CPE= 1.0, IW: CPE= 0.9, IW: CPE= 0.8 and IW: CPE= 0.7). Results of present study reveals that the crop sown on thermal environment of 3rd December took maximum duration (113), GDD (1595.7°C days), HTU (11,146.3°C days hours), PTU (16,628.6°C days hours), HUE (2.97 kg ha-1°C-1 day), HTUE (0.43 kg ha-1°C-1 day), and PTUE (0.28 kg ha-1°C-1 day). Among irrigation schedule I1 (IW: CPE= 1.0) attained maximum crop duration (103 days), GDD (1513.8°C days), HTU (10,550.0°C days hours), PTU (15,461.3°C days hours), HUE (2.96 kg ha-1°C-1 day), HTUE (0.43 kg ha-1°C-1 day) and PTUE (0.29 kg ha-1°C-1 day). As regards varieties, MP 3336 took maximum duration (104), GDD (1548.1°C days), HTU (10818.9°C days hours), PTU (15863.5°C days hours), HUE (2.84 kg ha-1°C-1 day), HTUE (0.41 kg ha-1°C-1 day) and PTUE (0.28 kg ha-1°C-1 day). The heat unit indices decrease during vegetative stages but increases during reproductive phase. The crop duration, heat indices (GDD, HTU, PTU and PTI), HUE, HTUE, PTUE and grain yield was higher under thermal environment of 3rd December sown crop with irrigation schedule I1 (IW: CPE= 1.0) and wheat variety MP 3336.