Effects of dates of sowing on phenology, thermal and radiation regimes, and yield of wheat

To assess the effects of thermal and radiation regimes on wheat, a field experiment consisting of five dates of sowing starting from 20 November at weekly interval, was conducted. The crop sown on 20 November needed 113 days to attain maturity and with delay in sowing dates, maturity durations decreased upto 91 days in 18 December sown crop. The highest thermal and radiation regimes of 2095 degrees C day for GDD, 15515 degrees C day h for HTU, 31880 degrees C day h for PTU and 2140 mmol m(-2) for PAR were associated with maximum yield from crop sown on 20 November. Accumulated global radiation and PAR during vegetative phase showed significant positive correlation, but during reproductive and grain filling phases they exhibited significant negative correlation with dry matter. Accumulated GDD during vegetative, entire growth period and grain filling period registered significant positive correlation with grain yield. Accumulated HTU, PTU, global radiation and PAR, prevailing during reproductive and grain filling phases, showed significant negative association with grain yield. Because of higher values of HUE, HTUE, PTUE, RAUE and PARUE, in terms of grain yield, amounting to 0.1614 g m(-2)GDD, 0.02199 m(-2)HTU, 0.0104 g m(-2)PTU, 0.2220 g MJ(-1) and 0.1599 g mmol(-1), respectively, the 20 November sown crop was adjudged as the optimum time of sowing. R-2 of regression models was significant at 1% level, accounting for 97 to 99% variation in total grain yield.