Changes in Chemical Composition of Australian Waxflowers Due to Soil Applications of Nitrogen and Assessment of Nitrogen Status by Tissue Analysis

Abstract

Three field experiments were conducted to investigate the effects of soil-applied nitrogen (N) on plant chemical composition, nutrient removal, and the use of plant analysis to assess N status of Australian waxflowers. Experiments were conducted in commercial plantings of Chamelaucium uncinatum cultivar Alba and a Chamelaucium hybrid (C. floriferum  C. uncinatum) known locally as Walpole wax, at 3 sites in South Australia. Nitrogen, as ammonium nitrate, was applied at rates up to 160 g plant À1 over several side dressings during the growing season. To assess plant nutrient status, stem tips (25-40 mm long tips of stems) were sampled during the growing season and whole stems at harvest.Nitrogen concentration in both stem tips and whole stems was sensitive to variations in N supply; however, the magnitude of the effect varied between sampling times and sites. In stem tips sampled during spring, the increase in N concentrations ranged from 19.8% at site 2 to 74.6% at site 1. Nitrogen concentrations in stem tips were consistently greater than concentrations in whole stems. The application of N decreased phosphorus (P) concentrations in whole stems and copper (Cu) concentrations in stem tips and whole stems. There was no consistent effect of applied N on potassium (K), calcium (Ca), magnesium (Mg), boron (B), zinc (Zn), and manganese (Mn) concentrations in either plant part sampled. Nutrient removal by flowering stems, in order from greatest to least, was N > K > Ca > P > Mg > Mn > B > Zn > Cu.Based on 1800 plants ha À1 , it was estimated that for N, P, and K, 121.9, 15.4, 60.1 kg ha À1 , respectively, was removed in harvested stems. Based on poor sensitivity, the lack of a sharp transition zone between deficient and adequate N concentrations and the lack of consistent relationships between N concentration in stem tips and yield response, it is concluded that N concentration in stem tips is not a useful indicator of the N status of waxflower plants.