Heat unit requirement and yield of wheat (Triticum aestivum L.) varieties under different growing environment in mid hill conditions of Himachal Pradesh

A eld experiment was conducted during rabi seasons of 2015-16 and 2016-17 to study the accumulated growing degree days (GDD), helio-thermal unit (HTU), photo-thermal unit (PTU), heat use efciencies (HUE) at different phenological stages and performance of wheat (Triticum aestivum L.) varieties grown under different sowing dates. Results of present study revealed that the crop sown on 20th October required maximum calendar days, growing degree days, photo-thermal unit and helio-thermal unit for tillering, owering, earing and maturity which was signicantly reduced with subsequent delay in sowing time. The grain yield recorded in 20th November (4065 kgha-1) was statistically at par with 5th November yield (3863 kgha-1). The signicant reduction in grain yield on varieties was recorded when sowing was delayed beyond 20th November. Among the varieties 'VL-907' produced highest grain yield(3771 kgha-1) which was statistically on par with 'VL-829' (3726 kgha-1). The early and timely sown wheat  variety like VL-829 and VL-907 took highest calendar days, GDD, HTU and PTU for earing and maturity. The variety 'VL-907' recorded the highest grain yield (4196 and 4168 kgha-1) at 5th and 20th November sowing as compared to all other sowing dates.