Author(s):

Shrabani Basu, Pramiti K Chakraborty, R Nath and PK Chakraborty

Abstract: Temperature, one of the prime weather factors significantly influences crop growth processes. The thermal indices like growing degree day (GDD), Helio-thermal unit (HTU) are useful to predict the onset of different phenophases, growth behavior and yield. Greengram, being short duration and photo-thermo sensitive, is influenced by prevailing thermal regime. To assess the crop phenology and yield behavior under existing thermal regime, a two year field experiment was conducted during the spring-summer seasons in 2011 and 2012 at District Seed Farm, Bidhan Chandra Krishi Viswavidyalaya, Kalyani, West Bengal, India in split-plot design with three replications. Four dates of sowing (15^th February, 25^th February, 7^th March, 17^th March) had been placed as main plot treatment and five varieties (IPM-2-3, <em>Samrat,</em> Pant Mung-5, <em>Sonali </em>and <em>Meha</em>) as sub-plot treatment. Observations started from sowing and continued upto pod maturity with coverage of branch initiation, bud emergence, 100% flower emergence and pod emergence stages. Calculations on cumulative GDD, HTU and their impact on seed yield suggested that maximum cumulative GDD was noted under D₃ sowing in both the year during sowing to germination (107.6 and 112.7 day °C in 2011 and 2012 respectively). The cumulative GDD requirement at pod maturity under D₂, D₃ and D₄ sowing was higher in second year than first year. There is a gradual increase of cumulative HTU from vegetative to reproductive stage irrespective of dates of sowing. The cumulative HTU at pod maturity stage recorded higher in 2012 as compared to 2011. The variation in duration of phenophases caused by the variation of thermal regime. Both GDD and HTU for all the phenophases positively and significantly affected the seed yield in the first year whereas in second year, the impact was negative but insignificant in bud and pod emergence stages.

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