Field experiment was initiated in June 2000 in the same block of the research farm. The experiment was laid out in a randomized block design with five treatments on stage of crop harvest (pre-flowering and 25%, 50%, 75% and 100% flowering) and four replications, individual plots being 3 × 6 m. Each plot received uniform dose of neem cake 900 g (0.5 t/ha), di-ammonium phosphate 155 g (40 Kg P₂O₅ /ha) and muriate of potash 120 g (40 kg K₂O/ha) as basal dose which was incorporated with 5 cm top soil using hand hoe. Ocimum gratissimum seedlings, six weeks old, were planted at 60 cm row-to-row and 45 cm plant-to-plant spacing in June 2000. The field was irrigated immediately after planting for early establishment of the seedlings. Thereafter, the field was irrigated 11 and 13 times in the first and second year of experimentation, respectively. Nitrogen at 120 kg/ha was applied in the form of urea spreading over all the harvests per annum. The crop received fi ve and four hand weedings during first and second year of experimentation. Apical part (25-35 cm) of all the branches was harvested in all the treatments as given below: (Pre-flowering Year1 September 20 and November 12, 2000 and January 16, March 17 and May 16, 2001; Year2 July 20, September 13 and November 17, 2001 and January 27, April 7 and June 16, 2002); (25% flowering Year1 September 26 and November 25, 2000 and February 3, April 9 and June 13, 2001; Year2 August 17, October 16 and December 26, 2001 and March 11 and May 25, 2002); (50% flowering Year1 September 30 and December 4, 2000 and February 17, April 28 and July 7, 2001; Year2 September 10 and November 14, 2001 and January 24, April 9 and June 23, 2002); (75% flowering Year1 October 7 and December 16, 2000 and March 6 and May 20, 2001; Year2 August 3, October 12 and December 21, 2001 and March 6 and May 25, 2002); (100% flowering Year1 October 15 and December 29, 2000 and March 24 and June 12, 2001; Year2 August 31 and November 14, 2001 and January 28, April 18 and July 7, 2002).

Harvesting at pre-flowering produced 12.5%, 24.1%, 35.5% and 50.0% higher biomass yield compared to harvesting at 25%, 50%, 75% and 100% flowering, respectively, in the first year of cropping. The respective increase was 16.8%, 22.0%, 38.2% and 63.2% in the second year. Late harvested crop (100% flowering) contained the highest amount of essential oil and it decreased in the order of harvesting at 100% flowering > 75% flowering > 50% flowering > 25% flowering > pre-flowering treatment. The total oil yield was, however, significantly higher (15.8-19.9% and 12.7-33.6% in first and second years, respectively) with pre-flowering compared to all other harvest treatments. Pre-flowering harvested crop produced oil containing the highest amount of eugenol and it decreased in the order of harvesting at pre-flowering > 25% flowering > 50% flowering > 75% flowering > 100% flowering treatment.