International Journal of Plant & Soil Science

Agrometeorological assessment of crop phenology and productivity helps to understand crop–weather relationships and the effects of thermal and radiation resources on crop performance. In rainfed areas, where crop development is strongly influenced by prevailing weather conditions, thermal indices are useful for assessing phenological development, resource-use efficiency and yield. A field experiment was conducted during the Kharif season of 2022 at the Research Farm Area, Department of Agricultural Meteorology, CCS Haryana Agricultural University, Hisar, to study the effect of sowing dates and varieties on phenology, thermal indices, heat use efficiency and yield of rainfed pearl millet under semi-arid conditions. The experiment was laid out in a factorial randomised block design with three sowing dates (24^th June, 18^th July and 10^th August) and three varieties (GHB 558, HHB 67 Improved and HHB 197), with four replications. Growing degree days, heliothermal units, photothermal units and heat use efficiency were calculated to assess the thermal and radiation conditions during crop growth. Heavy rainfall of 190.8 mm during Standard Meteorological Weeks 38^th–39^th caused prolonged waterlogging in the 10^th August sown crop, severely damaging it before physiological maturity. The 24^th June sown crop recorded greater accumulation of growing degree days, heliothermal units and photothermal units, a longer crop duration and a higher grain yield (3974.5 kg ha⁻¹) than the 18^th July sowing (2976.3 kg ha⁻¹). It also recorded higher heat use efficiency (2.49 kg ha⁻¹ °Cday⁻¹) than the 18^th July sowing (2.06 kg ha⁻¹ °Cday⁻¹). Among varieties, GHB 558 recorded the highest grain yield (4026.0 kg ha⁻¹), 1000-grain weight (9.98 g), biological yield (14531.3 kg ha⁻¹) and heat use efficiency (2.58 kg ha⁻¹ °Cday⁻¹). Delayed sowing reduced the accumulation of thermal indices and shortened the crop growing period. Grain yield showed significant positive relationships with growing degree days (r = 0.72**), heliothermal units (r = 0.73**) and photothermal units (r = 0.71**), while bright sunshine hours showed a strong positive relationship (r = 0.96**) and evening relative humidity showed a negative relationship (r = −0.84*). Regression analysis showed strong relationships between thermal indices and phenological development (R² = 0.97–0.99), whereas the combined model incorporating growing degree days, heliothermal units and photothermal units explained 54.2 per cent of the variation in grain yield (R² = 0.542, p = 0.001). The study indicated that timely sowing during late June, particularly with GHB 558, resulted in better utilisation of thermal resources and higher productivity of rainfed pearl millet, while delayed sowing increased the risk of yield reduction due to unfavourable weather conditions.