Photothermal Quotient-An Effective Thermal Index for Evaluation of Lentil (Lens culinaris L.) Phenology and Yield in the Lower Gangetic Plains

Sowing time and variety-specific genetics influence the phenological development of lentil (Lens culinaris L.), affecting its heat and solar energy utilization for attaining satisfactory yield. The present study was conducted to assess how the different thermal indices behaved in explaining variation in phenology and yield components with corresponding effects on yield of lentil varieties grown under varying sowing dates.

The experiment comprised of four sowing dates in the main plots and five lentil varieties in the sub-plots, laid out in a split- plot design replicated thrice. The phenology, yield components and yield were recorded. The computed thermal indices and correlation and regression analyses were used to assess their effects on yield traits and yield.

Sowing after 7^th November reduced lentil yield by 13.6-22.5 kg ha^-1 day^-1 and 0.9-2.1% ha^-1 day^-1 on absolute and relative basis, respectively. The varieties WBL 77 and HUL 57 were less sensitive to temperature fluctuations resulting in stable yield performance under varying thermal regimes. Despite significant influence of temperature on yield traits, growing degree days explained 82.0-89.0%, while photothermal quotient (PTQ) explained 92.0-96.0% of the total variation in yield. PTQ emerged as a reliable yield predicting thermal index and might be used for breeding climate-smart lentil varieties.