Improving yield and heat use efficiency of broccoli (Brassica oleracea L. var italica) grown under abiotic stresses in the mid-hill of Himachal Pradesh

Abstract: A field experiment was conducted in the mid-hill zone of Himachal Pradesh representing the sub-humid zone to study the phenological behaviour and heat use efficiency of broccoli crop under abiotic stresses. The broccoli variety, Sakata was evaluated under three thermal environments (T₁- 8^th October, T₂ -28^th October and T₃- 18^th November). To expose the crop to different thermal environments, two mulching levels (M₁-with black mulch and M₂- without mulch) and two irrigation levels (I₁- Irrigation at different phenological stages I₂- rainfed conditions), during rabi season of 2021-22. The experiment was laid out in a factorial randomized complete block design with three replications. Different agroclimatic indices were computed viz., accumulated growing degree days, helio-thermal units, photothermal units and heat use efficiency. The regression models were developed between the agroclimatic indices, yield and dry matter accumulation of crop. It was found that the broccoli crop sown on 28^th October (the normal date of transplanting) took maximum (132) days to reach maturity. The number of days required to attain different phenological stages decreased with delayed sowing. The accumulated growing degree days requirement at the harvesting stage (921.4 ºC day) was observed maximum in timely transplanted (28^th October) crop resulting in a higher yield per plot (10.4 kg) and decreased with late transplanted (18^th November) crop. The crop utilized heat more efficiently under a timely sown crop. The highest heat use efficiency (HUE) was observed in the crop sown on 28^th October and 8^th October (27.37 and 25.35 kg/ha/°C/day), respectively. The regression models were developed between curd yield, dry matter accumulation and thermal units of the crop. The model explained 0.50, 0.44 and 0.47 variations in curd yield whereas 0.69, 0.58 and 0.63 variations in dry matter accumulation with different agroclimatic indices under different transplanted dates, mulching and irrigation levels respectively. Broccoli cultivation yielded a profit of ?5.17 lakhs/ha, demonstrating its profitability for farmers. The study highlighted that timely sowing, black mulch, and optimal irrigation significantly improved heat utilization efficiency in mid-hill sub-humid regions. Black mulch improved soil moisture and temperature, creating ideal conditions for broccoli, a thermo-sensitive crop.