The effects of nitrogen (N) and potassium (K) on stem growth and yield responses of Australian waxflowers were investigated. Experiments were conducted in commercial plantings at 3 sites in South Australia. Plantings of Chamelaucium uncinatum cvv. Alba (2 sites) and Purple Pride (1 site) and a Chamelaucium hybrid (C. floriferum x C. uncinatum), known locally as Walpole wax (1 site), were 3-5 years old when the study began in 1990. Nitrogen and K were applied at rates up to 160 g N and 80 g K/plant.year. Application of N significantly (P<0.05) increased stem growth, with the magnitude varying considerably between sites and years. Increasing the rate of applied N from 0 to 80 or 160 g/plant.year increased mean tip-growth of flowering stems of cv. Alba by 47.7% at site 1 and 137.1% at site 3, and of Walpole wax by 144.2% at site 2. In contrast, the effect on cv. Purple Pride was minimal. Tip-growth also varied significantly (P<0.05) between sites. Applied K did not significantly affect stem growth at any site. Application of N significantly (P<0.05) increased the yield of 41-70 and >70 cm stems, and total stem yield at all sites with variation between years and cultivars. For example at site 2 increasing the applied N rate from 0 to 80 or 160 g/plant .year increased total stem yield by 13.9, 176.2 and 77.6% in 1991, 1992 and 1993, respectively. In contrast, the effect of applying K was inconsistent. Application of N significantly increased the weight of prunings at all sites and yield of prunings also varied between years. Applied K significantly affected the yield of prunings at site 3, where application of 80 compared with 0 g1plant.year decreased the yield by 17.9%. For all sites, the mean ratios between total stem weight and total biomass harvested were in the range 0.68-0.82. The effect of applied N was only significant at site 3, where the ratio decreased from 0.76 to 0.57 when the rate of applied N increased from 0 to 160 g/plant.year. The effect of K was not significant at any site. At sites 1 and 2, and for cv. Alba at site 3, application of 80 or 160 g N1plant.year decreased mean stem dry matter by 8.0, 9.3 and 11.0%, respectively. Stem dry matter content also varied significantly between years at all sites. The effect of applied K was only significant at site 3, where application of 80 g1plant.year reduced dry matter content by 5.3% compared with 34.2% for the nil rate. Based on data for all sites, stem fractionation showed that dry matter yields (as a percentage of total stem dry weight), were in the order, woody tissue (3 15-49.9%) > leaves (22.1-29.2%) > flowers (15.9-25.8%) > tip-growth (5.0-21.9%). The effect of applied K on the yield of the different stem parts was only significant (P<0.05) at site 1, where in 1991 yield of the tip-growth fraction decreased. We conclude that to develop effective N fertiliser strategies for waxflowers requires knowledge of (i) soil type, in particular residual N fertility; (ii) annual vegetative growth cycle (i.e. periods of growth flushing); (iii) harvest period; and (iv) flowering time. For cultivars or hybrids harvested when vegetative growth is negligible (e.g. winter) N nutrition can be optimised, while for those harvested during periods of vegetative flushing (e.g. September-November) lower rates of N should be applied to ensure tip-growth is not excessive. Although yield responses to applied K were inconsistent, we recommend 20 g K/plant.year to ensure that productivity is maintained over the 5-10 years flowering stems can be harvested from commercial plantings.
GROWTH AND YIELD RESPONSES OF TRIPLOID WATERMELONS TO FERTILIZER SOURCE AND RATE, MULCH, AND ROW COVER
