Thermal heat requirement as well as energy components depend on weather parameters. Critical phenological stages was taken into consideration for the thermal heat requirement during 2013-15 under fertigation treatment (25, 50 and 75 per cent of recommended fertilizer dose) in mango cv Dashehari at Lucknow region. Mango productivity varied from 4.54-11.84 t ha-1 across different fertigationregimes as a result of differential thermal heat accumulation. In the treatment 25 per cent RDF,

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... y of 5.23, 11.13 and 6.12 t ha-1 was recorded during 2013, 2014 and 2015 while in 50 per cent RDF, 6.23, 11.84 and 7.76 t ha-1 was observed. The maximum yield reduction (37.5, 14 and 26.1%) was found in control plot. A significant variation in radiation energy received during the field experiment was revealed and a range of 8.97 to 16.27 mm day-1 extraterrestrial radiation was observed at different critical phenological stages. The heat use efficiency (HUE) varied between 2.54-6.78 g m-2°Cd-1 across seasons and treatments. Water use efficiency (WUE) of 10.8, 14.1, 13.5 and 11.7 kg fruits m-3 was recorded in different fertigated treatments. The highest reduction in WUE was noted in control (23.9%) followed by 17.2 and 4.8% in 25 and 50 per cent as compared to 75 per cent fertigation regimes.