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ABSTRACT The effect of row spacings (45, 60 and 75 cm) and various amounts of nitrogen fertilizer (0,100,200 and 300 kg N/ha) on plant growth, essential oil production and composition of Scotch spearmint was studied in the field during 1987 and 1988 in Lucknow, India. Nitrogen application increased plant height and leaf area index while decreased leaf-stem ratio and oil concentration, irrespective of row spacings. The green herbage and oil yields increased significantly up to an application of 200 kg N/ha at 45 or 60 cm row spacing as against up to 300 kg N/ha at 75 cm row spacing. The higher N application at 75 cm row spacing, however, did not increase oil yield compared to application of 200 kg N/ha at 60 cm row spacing. Row spacing influenced various response functions and optimum N rate. At optimum N, response per kg N, net return per kg N and benefit-cost ratio were highest at 60 cm row spacing. Oil concentration and composition in green herb were related to leaf area index and N concentration in the plant. Both the oil concentration and the carvone concentration in oil decreased, while the limonene concentration increased with increasing leaf area index and N concentration. The role of row spacing and, particularly N, on crop maturity is emphasized in securing both highest yields and quality of Scotch spearmint oil. KEY WORD INDEX: Mentha gracilis LabiataeScotch spearmintrow spacingnitrogen fertilizer effect
Kothari et al. (Mon,) studied this question.