Response of palmarosa {Cymbopogon martinii (Roxb.) Wats. var. motia Burk.} to foliar application of magnesium and micronutrients

A field investigation was carried out on red sandy soil in the semi-arid tropical climate of south India to investigate the response of industrially important, multi-harvest, aromatic crop palmarosa {Cymbopogon martinii (Roxb.) Wats. var. motia Burk., family: Poaceae} to foliar application (2.5 g/L single application for each harvest at 700 L nutrient solution per hectare) of magnesium (Mg), manganese (Mn), iron (Fe), zinc (Zn), boron (B) and their residual effect on the succeeding harvest. During the experimental period, palmarosa crop afforded four harvests, 49.5-70.6 t/ha total biomass yield (fresh weight), 211.4-384.2 kg/ha total essential oil yield and Rs. 232,540-422,620/ha (US$ 4844.6-8804.6/ha) gross returns. Fifth harvest (no nutrients were applied) performed to examine the residual effect of Mg and micronutrients applied to the previous four harvests revealed the absence of residual effect pointing to the need for application of nutrients to individual harvests. Foliar application of Mg and micronutrients significantly increased the yield attributes (plant height, tiller number/plant, leaf number/plant), biomass yield, essential oil yield and gross returns of palmarosa. Mg and micronutrients enhanced the total biomass yields by 37.0-42.6% and the total essential oil yields by 44.6-81.7% in comparison to the control (water spray).All the treatments produced good quality essential oils with 1.5-3.2% linalool, 79.7-85.8% geraniol and 4.5-10.3% geranyl acetate. Mg and B additions declined linalool (%) in the second and fourth harvests and increased geraniol (%) in the first harvest. Mg and micronutrients application improved geraniol (%) in the second harvest. Except Zn, all the other nutrients decreased geranyl acetate (%) in the second harvest, but in the third and fourth harvests Mn and B increased geranyl acetate (%).