In a field study over two crop seasons over four dates of sowing (Oct.1, Oct. 20, Nov. 10 and Nov.30), barley cultivars VJM 201 and PL 172 attained harvest maturity in 120 to 161 days and 117 to 155.5 days, respectively under climatic conditions of Ludhiana. The growing degree days and heliothermal units required to attain different stages were worked out. It revealed that from sowing to harvesting the respective requirement of VJM 201 and PL 172 for GDD was 1314 to 2043°C days and 1274.5 to 1958.5°C days and for HTU was 8668.5 to 14116.5°C days hours and 8231 to 13472°C days hours. The linear regression models derived by using the phenophasic data for predicting the onset of particular phenophase of crop using either GDD or HTU indicated that GDD accounted for 87 & 85 per cent and HTU accounted for 74 & 72 per cent variation in onset of particular phenophase for barley variety VJM 201 and PL 172 respectively. Similarly, quadratic relationship derived between barley yield and heat units revealed that GDD and HTU accounted for 74 & 74 and 73 & 71 per cent variation in grain yield of barley variety VJM 201 and PL 172 respectively. Yield data indicate that crop sown on 20 October resulted in the production of the highest grain yield, but the advanced (Oct.1) as well as staggered (Nov. 10 and Nov.30) sown crop resulted in respective reduction of 28%, 14% and 37% over Oct. 20 sown crop. However, the highest heat unit accumulation viz. AGDD and AHTU were recorded under Oct. 1 sown crop due to prevalence of higher temperature in the first fortnight of October.
Accumulated Growing Degree Days, Accumulated Heliothermal Units, Barley, Date of sowing, Phenology
