Heat unit requirement and grain yield of wheat as influenced by thermal environment under Ludhiana conditions

The field experiment was conducted to study the effect of thermal environment on heat unit requirement and grain yield of wheat. Wheat was grown with three dates of sowing (20^th October, 5^th November, 20^th November) and three wheat varieties (Unnat PBW 343, PBW 725 and HD 2967) replicated thrice during rabi 2019–20 and 2020–21. Data of two rabi seasons was pooled to conduct analysis. Maximum calendar days (160 days) were taken by 20^th October sown crop to attain the physiological maturity followed by 5^th November (152 days) and 20^th November (148 days) sown crop. Maximum growing degree days were accumulated in 20^th October (1680.2°C day) sowing followed by 5^th November (1629.4°C day) and 20^th November (1516.4°C day) sowing. Maximum helio-thermal and photothermal units were accumulated in 20^th November (10279.1°C day hour,18036.4°C day hour) followed by 5^th November sowing (9838.4°C day hour, 17703.1°C day hour) and minimum in 20^th October (9495.7°C day hour, 16730.5°C day hour) sowing. The grain yield was significantly higher in early sowing (49.4 q/ha) followed by normal (46.5 q/ha) and late sowing (44.1 q/ha), respectively.