Accumulated heat unit requirement and yield of irrigated wheat (Triticum aestivum L.) varieties under different crop growing environment in central Punjab

Field experiment was conducted during rabi seasons of 2009-10 and 2010-11 to study the phenology, accumulation of growing degree days (GDD), helio-thermal unit (HTU), photo-thermal unit (PTU), pheno-thermal index (PTI) and performance of wheat (Triticum aestivum L.) varieties grown under different sowing dates. The crop sown on October 25 took maximum calendar days, growing degree days, photo-thermal unit and helio-thermal unit for 75% earing and maturity which got reduced significantly with subsequent delay in sowing time. The grain yield recorded in October 25 was statistically at par with November 5. The significant reduction in grain yield of timely sown varieties was recorded when sowing was delayed beyond November 15. Among the varieties ‘PBW 621’ recorded the highest grain yield which was statistically on par with ‘PBW 550’. The timely sown wheat varieties like ‘PBW 621’, ‘PBW 343’, ‘DBW 17’ and ‘WH 542’ took highest calendar days, GDD, HTU, PTU and PTI for earing and maturity. However, in medium duration varieties like ‘PBW 550’ the significant reduction was noticed when sowing was delayed beyond November 25. The variety ‘PBW 550" recorded the highest grain yield at November 15 sowing as compared to all other sowing dates.