~ 1038 ~ International Journal of Chemical Studies 2019; 7(3): 1038-1041 P-ISSN: 2349–8528 E-ISSN: 2321–4902 IJCS 2019; 7(3): 1038-1041 © 2019 IJCS Received: 09-03-2019 Accepted: 13-04-2019 Surya Prakash Singh Assistant Professor, Faculty of Agricultural Sciences, Arunachal University of Studies, Namsai, Arunachal Pradesh, India Pranamika Sharma Assistant Professor, Faculty of Agricultural Sciences, Arunachal University of Studies, Namsai, Arunachal Pradesh, India Anil Kumar Jena Assistant Professor, Faculty of Agricultural Sciences, Arunachal University of Studies, Namsai, Arunachal Pradesh, India Tara Bhuyan Assistant Professor, Faculty of Agricultural Sciences, Arunachal University of Studies, Namsai, Arunachal Pradesh, India Rimi Deuri Assistant Professor, Faculty of Agricultural Sciences, Arunachal University of Studies, Namsai, Arunachal Pradesh, India Toyir Nyori Assistant Professor, Faculty of Agricultural Sciences, Arunachal University of Studies, Namsai, Arunachal Pradesh, India Correspondence Surya Prakash Singh Assistant Professor, Faculty of Agricultural Sciences, Arunachal University of Studies, Namsai, Arunachal Pradesh, India Heat unit requirement of mustard ( Brassica Juncea L.) under different thermal regimes and irrigated conditions of Namsai region of Arunachal Pradesh Surya Prakash Singh, Pranamika Sharma, Anil Kumar Jena, Tara Bhuyan, Rimi Deuri and Toyir Nyori Abstract Field experiments were conducted under Arunachal University of Studies, Namsai, Arunachal Pradesh during 2017-18 to 2018-19 on mustard crop was sown on three dates (10th October, 20th October, and 30th October) with three irrigation treatments. The results indicated that the number of days required for attaining different phenological stages decreased with the delay in sowing. For all the phenological stages, crop sown on 10th October consumed higher heat units and consequently resulted in higher yield and heat use efficiency (HUE) than that of another sowing. However, higher pheno-thermal index (PTI) values were observed for the late sown crop i.e. 10th October. Further, among the irrigation treatments, three irrigations throughout the growing period showed an increase in days to physiological maturity as well as heat units and HUE for grain and biological yield as compared to other treatments. Three irrigations throughout the growing period increased the grain yield by 72 percent and biological yield by 54 percent than that of one irrigation at before flowering stage. The GDD also showed a highly significant positive correlation with grain and biological yield. Therefore, it may be used for forecasting the phenological stages and yield under different sowing date and stage-based irrigation scheduling for mustard. Keywords: Phenological stages, pheno-thermal index, growing degree days, and heat use efficiency Introduction Mustard is one of the most prominent oilseed crops next to groundnut in India. It contributes to a large extent in the national economy and accounts for nearly 28.6% of the total oilseeds production in the country. Wheat being a thermo-sensitive and moisture sensitive crop, the sowing time and irrigation management are two most critical factors that need proper identification for proper crop growth achieving better yield. The crop sown on different sowing dates exposed to a variety of weather conditions during phenological stages affects its growth rate and yield. Mustard is grown in the tropical and temperate climate and is grown in a winter season. Among all the weather parameters, temperature plays a significant role in better establishment, growth, development and finally the yield of the crop. It requires about 18-25 0 C temperature and low humidity for better crop growth. During seed germination and maturity stage slightly high temperature is required. Optimum temperature is 25 0 C. Rainfall, cloudiness and extreme cold and frost are harmful to the crop (Mukherjee et. al., 2014) [4] . Rapeseed-mustard crop needs assured amount of accumulated heat at various phenophase to meet the proper growth and development. Agrometeorological 3 indices such as growing degree days (GDD), photo-thermal unit (PTU), heliothermal unit (HTU), photo-thermal index (PTI) and heat use efficiency (HUE) mostly used as weather-based parameters for accurate estimation of the timing of occurrence of different crop phenophase. The quantification of heat use efficiency is helpful for the assessment of yield potential of any crop under different thermal environments. Due to less time available for transport of photosynthate to sink, yield reduction occurs in late sown crops as compared to early and normal sown crop (Roy et. al., 2005) [7] . Kaur et al., (2006) [3] reported that delayed sowing of the crop greatly suppressed various growth and yield components including plant height, numbers of flowers and siliquae and the number of seeds per siliqua. The seed yield decreased by 46% in the delayed sown crop.