Putting back what we take out, but how much Phosphorus and nitrogen additions to farmed Leucadendron 'Safari Sunset' and Leucospermum 'Succession' (Proteaceae)

H. Hawkins, H. Hettasch, Michael Cramer

    Research output: Contribution to journalArticle

    12 Citations (Scopus)

    Abstract

    Proteaceae are adapted to low-nutrient soils in the various regions where they occur. However, harvesting of flowering stems for the cut-flower industry must eventually cause soil nutrient depletion sufficient to reduce yields. Different N forms, and N and P concentrations were supplied to two Proteaceae cultivars (Leucadendron 'Safari Sunset' and Leucospermum 'Succession') in a controlled ferfigation experiment, and appropriate concentrations for maximum growth with minimum nutrient accumulation or loss were determined. Small additions of N (0.025-0.1 mM) significantly improved growth of both cultivars growing on Strandveld sandy soil. Larger additions of N (up to 2 MM N) resulted in poor growth (both cultivars) and N accumulation in the soil (Safari Sunset). Small additions of P (< 10 mu M) significantly improved growth of both cultivars and resulted in no accumulation or loss of P in the soil. Larger additions of P (up to 500 mu M) resulted in poor growth, P toxicity symptoms and P leaching from the upper soil layers. Best N forms in descending order of both plant visual appearance and vegetative yield were: urea >= ammonium nitrate > ammonium sulphate > calcium nitrate. Phosphorus toxicity symptoms were associated with increased concentrations of leaf P, Ca and Fe. Under conditions of maximum growth (10 mu M P and 0.1 mM N) Safari Sunset removed 18 +/- 0.6 g N, 1.5 +/- 0.1 g P, 5.3 +/- 0.6 g K and Succession removed 5.5 +/- 0.2 g N, 0.3 +/- 0.02 g P, 3.1 +/- 0.5 g K over 6 months. At maximum growth, plants acquired more N and P amounts than were supplied, but supplying higher N and P concentrations adversely affected growth. Thus, a more complex or slow-release form of N and P than urea and soluble phosphate, respectively, may provide enough N and P to replace losses from the farm soil at the low concentrations required for proteas. (c) 2006 Published by Elsevier B.V.
    Original languageEnglish
    Pages (from-to)378-388
    JournalScientia Horticulturae
    Volume111
    Issue number4
    DOIs
    Publication statusPublished - 2007

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