Phenology, thermal indices and yield of summer greengram [Vigna radiata (L.) Wilczek] under different sowing dates in Gangetic plains of West Bengal

A field experiment was conducted to study the effect of four sowing dates (1 February, 15 February, 1 March and 15 March) on four varieties (Samrat, Meha, Sonali, Sukumar) of greengram during pre-kharif (summer) season of 2016 at 'C ’Block Farm of Bidhan Chandra Krishi Viswavidyalaya, Kalyani, Nadia, West Bengal, India. Mean cultivar days from sowing to emergence, flower initiation, pod initiation and maturity of greengram crop were 4.4, 43.5, 53.3 and 74.8 days, respectively. The duration of greengram was reduced successively with delay in sowing from 1 February (77.5 days) to 15 March (71.7 days). The average summed growing degree days (GDD), heliothermal units (HTU) and photothermal units (PTU) for life cycle were recorded as 1477°C day, 11212°C hour and 18047°C hour, respectively. Greengram sown on 1 March produced the highest grain yield (762.5 kg/ha) being at par with 15 February (745.0 kg/ha), which was 8.1 and 13.8% greater over 1 February and 15 March sowings, respectively. The correlations between thermal indices and grain yield revealed that GDD (r=0.444**), HTU (r=0.493**) and PTU (r=0.473**) during pod initiation to maturity had positive effect (P<0.01) on economic yield of greengram in the investigation. Based on grain yield, four varieties could be arranged as: Sukumar (765.6 kg/ha) > Samrat (720.3 kg/ha) > Meha (709.7 kg/ha) > Sonali (686.6 kg/ha). Protein content in grain of greengram remained unaffected due to differences in sowing time during summer, while Samrat had maximum protein content (22.2%).