Agricultural Research Journal

Sunflower (Helianthus annuus L.) is a thermo-and photo-insensitive crop but environmental, nutritional and hormonal factors can cause variation in phasic development and energy utilization efficiency of crop. A study was conducted to investiagate crop phenology and thermal energy utilization efficiency of spring sunflower in relation to foliar application of boron and TIBA under staggered sowing (20 January, 10 February and 2 March). Early sown crop took significantly more number of days to attain all phenological stages. Foliar application of boron and TIBA increased the number of days to attain flowering and subsequent stages. The thermal units required to attain various phenological stages increased progressively due to delay in sowing but accumulated growing degree days for physiological maturity decreased with delay in sowing. Boron and TIBA treatments recorded markedly higher thermal units accumulation as compared to control for physiological maturity. Phenothermal index gradually increased from star bud to physiological maturity under all treatments. Late sown crop exhibited higher heat use efficiency at 30 DAS, but at 90 DAS and at harvest foliar application of boron and TIBA improved heat use efficiency of the crop.