Effects of applied nitrogen fertiliser on the chemical composition of the essential oil of three Leptospermum spp

Abstract

Three native species of Leptospermum (L. petersonii, L. Flavescens, L. luehmannii) were grown in an amended podsolic soil under 4 nitrogen (N) levels, 0, 20, 40 and 60 kg Nha, supplied as NH4N03. Plants were harvested after 16 weeks growth, leaves were separated from stems, and essential oil was distilled from leaves by steam distillation. Extracted oils were analysed for their components by gas chromatography. Oil density from L. petersonii was also determined. Growth and oil yield of the 3 Leptospermum species showed no response to N fertilisation. However, the oil composition in L. petersonii and L. flavescens leaves was affected. The greatest response was in the geranial and citronella1 contents in L. petersonii, which peaked in the 40 kg N/ha treatment. This is the first known report of the manipulation of essential oil composition of Australian native plants by N fertilisation. The low optimal level of N fertiliser required for maximum production of valuable oil components indicates that Leptospermum spp. are suitable for infertile soils. The low ß-pinene yield of L. luehmannii makes it unsuitable for commercial exploitation.