Effect of different microenvironment on heat unit requirement and heat use efficiency of different lentil genotypes sown in rice fallow condition

To utilize the rice (Oryza sativa L.) fallow land of the northeastern region (NER) of India and enhance the cropping intensity, a set of lentil (Lens culinaris) genotypes/varieties were evaluated for heat requirement and use efficiency under 2 thermal regimes in Tripura [altitude of 52 m ASL (meter above sea level)] during 2014–15 and 2015–16 (November to March). The experiment consisted of 14 lentil genotypes namely ‘HUL 57’, ‘L 4076’, ‘ILL 10897’, ‘ILL 10893’, ‘BM 6’, ‘BM 7’, ‘WBL 77’, ‘Subrata’, ‘ILL-6002’, ‘L-1111-12’, ‘L-1112-18’, ‘L-1112-20’, ‘ILL-10951’, and ‘L 1112–07’ which were sown under two thermal regimes e.g., 16^th November (1^st date of sowing) and 1^st December (2^nd date of sowing) during both the years. Results revealed that crop sown on 16^th November took 3 days more than that of 1^st December sowing to attain physiological maturity. ‘Lentil’ ‘L-1112-18’ took a minimum number of days (80) to reach physiological maturity stage followed by ‘L-1111-12’ (82 days). Crop sown on 1^st December consumed more growing degree days (GDD) between different phenological stages, for example sowing to 50% emergence (113.8), 1^st flower bud initiation to 50% flowering (250.4), and 50% flowering to physiological maturity (632.3) except for 50% emergence to 1^st flower bud initiation (682.4) than that of 16^th November sowing. Lentil variety HUL 57 required the highest GDD between all the phenological stages. Accumulated GDD and heliothermal unit (HTU) were higher for 16^th Nov sowing ranged from 100.4°C days (emergence) to 1719.5°C days (physiological maturity) and accumulated HTU from 127.6°C day hours (emergence) to 2199.2°C day hours (physiological maturity) than 1^st December sowing. HUL 57 accumulated the highest GDD and HTU from sowing to physiological maturity. The pheno-thermal index (PTI) was higher between sowing to 50% emergence (20.2–21.8) and 50% flowering to physiological maturity (18.2–20.1) than in between of 1^st flower bud initiation to 50% flowering (16.2–17.4) and 50% emergence to 1^st flower bud initiation (16.5–17.9). ‘Lentil’ ‘HUL 57’ had the highest PTI (21.3) followed by ‘L-4076’ (21.0) while the lowest PTI was by BM 6 (16.1) followed by 'L-1112-18 (17.1) between 50% flowering to physiological maturity. Lentil sown on 16^th Nov produced more seed (1008.9 kg/ha), straw (1608.9 kg/ha), and biomass (2617.6 kg/ha) yields, and improved heat use efficiency for grain yield (0.60 kg/ha°C day⁻¹) and biomass yield (1.56 kg/ha°C day⁻¹) than that of sowing on 1^st Dec. Lentil genotype BM-6 produced maximum seed yield (1270 kg/ha) followed by WBL 77 (1234 kg/ha) and L-1112-18 (1231.5 kg/ha). The highest straw yield was produced by WBL 77 (1747.5 kg/ha) followed by L-4076 (1715.5 kg/ha) and L-1112-18 (1685.5 kg/ha). However, genotype L-1112-18 produced maximum biomass yield (2917 kg/ha) followed by L-1111-12 (2894.5 kg/ha) and L-4076 (2883 kg/ha). The genotype L-1112-18 had maximum heat use efficiency for seed yield (0.90 kg/ha°C day⁻¹) and biomass yield (2.12 kg/ha°C day⁻¹). Thus, the study recommended the genotypes BM-6, WBL 77, and L-1112-18 which are heat efficient and high yielding for efficient utilization of rice fallow areas under both the thermal regimes.