Nitrogen and potassium nutrition of Australian waxflowers grown in siliceous sands. 1. Stem growth and yield responses

Abstract

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.

Seasonal Variation in Nutrient Status of Australian Waxflowers

“…At these sites, stem growth was greatest during summer-mid autumn and negligible during winter. [3] Similar trends have been reported for N concentrations in the leaves of pecan, [11] kiwifruit, [5] and custard apple; [12] and for nitrate-N in grapes. [14] Parvin [15] reported that N concentrations in leaves of Protea neriifolia were highest in spring and lowest in winter.…”

“…[13] In contrast with N, which is also considered to be a phloem mobile nutrient, P concentrations increased at sites 1, 2, and 3 (cultivar Purple Pride) over the period March-August. During this period, vegetative growth was minimal [3] therefore, leaves of stem tips sampled at the end of this period were older than those at the start, and it appears that P continued to accumulate as the leaves aged and concentrations increased during the remainder of this period. Other studies, for example with macadamia [16] reported low leaf P levels during winter, due to restricted root activity and low mobility of P in the soil.…”

“…1). During this period vegetative flushing occurred [3] and the decrease may be explained as a growth dilution effect. [13] In contrast with N, which is also considered to be a phloem mobile nutrient, P concentrations increased at sites 1, 2, and 3 (cultivar Purple Pride) over the period March-August.…”

“…Site, growth and yield details were described in Maier et al [3] Briefly, data were obtained from commercial plantings at three sites in South Australia. Sites 1 and 3 were located in the Lower South East and Lower Murray regions respectively, and site 2 was in the Mount Lofty Ranges.…”

“…[1] Waxflowers are often grown on sandy soils which have low nutrient status. [2,3] Further, continual removal of large amounts of biomass each year as marketable stems and prunings, may result in a gradual depletion of soil nutrient reserves. At present, growers in Australia have no calibrated plant or soil tests, to assess the nutrient status of their waxflower plantings.…”