Extinction coefficient and photosynthetically active radiation use efficiency of summer rice as influenced by transplanting dates

Aim : The present study was conducted to quantify, the extinction coefficient and photosynthetically active radiation (PAR) use efficiency of widely cultivated variety "Shatabdi" under changing dates of transplanting and to suggest the farmers for proper transplanting window in this zone. Methodology : Thirty five-day-old rice seedlings were transplanted during January and February at three different dates (D-1, D-2, and D-3) at a gap of 14 days with four irrigation regimes under strip plot design having three replications. Plant samples were taken at 14 days interval from each experiment and biometric parameters like LAI etc. and meteorological parameters like Incident PAR were estimated. Results : The results showed that the extinction coefficient decreased with delay in transplanting. The PAR use efficiency for biomass accumulation ranged from 2.07 to 2.19 g MJ(-1) when transplanting dates vaned from D-1 to D-3. The maximum grain yield was noted under D-1 or D-2 with no significant nation but a sharp reduction in yield was observed under D-3. The PAR use efficiency for grain yield was noted under D-2 (1.23 g MJ(-1)). The intercepted PAR at different phenophases significantly affected the grain yield. Interpretation : On the basis of radiation utilization efficiency the crop may be transplanted within first fortnight of February in this zone.