Lemongrass (Cymhopogon citrarus) was grown under irrigation in the Ord River Irrigation Area, Western Australia, on a sandy clay loam, to investigate its response to nitrogen (N) applications ranging from 0 to 1200 kg N/ha.year. Urea and ammonium sulphate were compared and they were not significantly different as N carriers. Six harvests were taken over a 390-day period, after an initial harvest 7 months after planting out. A curvilinear response was obtained over all N treatments with a linear response up to 600 kg/ha. At this level, fresh herbage, dry matter and oil yields for the 390 days were 115 t/ha, 28.4 t/ha and 433 L/ha, respectively. Higher N applications also increased tiller number and leaf area index, while depressing specific leaf area and oil content. The unharvested portion of lemongrass (i.e. stools, rhizomes and roots) decreased from 44 to 27% of total dry matter with additional N. The amount of N, P and K in the harvested herbage increased from 51, 8 and 121 kg/ha to 276, 30 and 357 kg/ha, respectively, for the 0 and 900 kg N/ha.year treatments. The N, P and K content of the unharvested portion was considerably less with 28, 6 and 27 kg/ha for 0 kg N/ha.year and 75, 9 and 32 kg/ha at the 900 kg N/ha.year level, respectively. The highest apparent N recovery was 31% at 600 kg N/ha.year and decreased with higher N applications. Considerable seasonal variation occurred within the 6 harvests for all components measured. © 1990 ASEG.
