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Nitrogen and phosphorus nutrition of kangaroo paw (anigozanthos pulcherrimus hooker)

Chilufya, Fred (1992) Nitrogen and phosphorus nutrition of kangaroo paw (anigozanthos pulcherrimus hooker). Masters by Research thesis, Murdoch University.

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Abstract

In the genus Anigozanthos, a number of species with different flower colour and mode of flowering have recently come into cultivation for cut-flower production in Western Australia where they are often grown on soils deficient in nitrogen and phosphorus. However, the requirements of these species for nitrogen and phosphorus for vegetative growth and optimal flower production are not well researched. In the present study, three glasshouse experiments and one field experiment were set up to study the nitrogen and phosphorus nutrition of the yellow kangaroo paw (Anigozanthos pulcherrimus Hooker). Clonal, tissue cultured plants were used in all experiments to reduce genetic variation.

The rates of nitrogen, phosphorus and potassium required for vegetative growth and the response of nitrogen and phosphorus concentrations in selected leaves to increasing rates of nitrogen and phosphorus supply were examined in the first glasshouse experiment. Four rates each of nitrogen (0, 20, 70 and 200 mg N/kg air dry soil), phosphorus (0, 10, 40 and 70 mg P/kg air dry soil) and potassium (0, 20, 70 and 200 mg K/kg air dry soil) were applied in a factorial combination to a sandy soil, to which adequate supplies of other nutrients were added. Plants were harvested 158 days after planting and the basal and the terminal portions of the elongating leaf (EL), the first leaf older than the youngest fully elongated leaf (YFEL + 1) and the third leaf older than the youngest fully elongated leaf (YFEL + 3) were sampled for nitrogen and phosphorus analyses. Maximum leaf , rhizome and sucker dry weights and number of suckers produced per plant were obtained at 70-200 mg N, 10-40 mg P and 20-70 mg K/kg air dry soil. Phosphorus toxicity developed in plants under high rates of phosphorus supply and was severe where nitrogen was in short supply. Phosphorus concentrations increased more strongly in the basal portions of leaves while nitrogen did not vary very much between the leaf portions. The terminal portion of the YFEL was chosen for nitrogen and the basal portion for phosphorus analyses.

Two concurrent glasshouse experiments were set on the same soil to determine critical nitrogen and phosphorus concentration ranges in selected leaf parts.

In the nitrogen experiment, plants were grown under ten rates (0,15, 30, 45, 60, 75, 90, 105, 120 and 135 mg N/kg air dry soil) of nitrogen supply. The terminal portion of the YFEL was sampled for nitrogen analysis 123 days after planting and the YFEL and EL were sampled at harvest, 161 days after planting. Plants grown without application of nitrogen had severe phosphorus toxicity symptoms. Plants grown under deficient nitrogen supply had a general pale green appearance. Increasing the nitrogen supply progressively increased leaf dry weights, number of suckers per plant and total number of leaves per plant without adverse effects at higher nitrogen levels. Nitrogen concentrations in both the terminal and basal portions of the YFEL and the EL were closely correlated with plant growth. The YFEL was chosen for determination of critical concentration ranges. Critical nitrogen concentration ranges for deficiency diagnosis and prognosis obtained from the relationship between leaf dry weight and nitrogen concentration in the terminal portion of the YFEL from hand fitted curves at 90 and 95% of maximum yield were 1.35-1.44% N for deficiency diagnosis and 1.72 - 2.02% N for predicting deficiency after a further 6 weeks of growth for 123 day old vegetatively growing plants.

Ten rates of phosphorus (0, 5, 10, 15, 20, 25, 30, 40, 50, and 60 mg P/kg air dry soil) were used in the phosphorus experiment. Application of low rates of phosphorus increased leaf and rhizome dry weights but high rates of phosphorus were toxic to the plants. The total number of leaves produced per plant was not reduced under phosphorus toxicity while the number of suckers produced per plant was slightly depressed. Phosphorus concentrations in the basal portions of the YFEL and the EL correlated well with plant growth suggesting that the basal portion was suitable for phosphorus analysis for deficiency and toxicity diagnosis. Critical phosphorus concentration ranges in the basal portion of the YFEL at 90 and 95% of maximum yieldwere 0.05-0.06% P and 0.24 - 0.29% P and 0.07 to 0.10% P for for diagnosis of deficiency and toxicity respectively. The critical phosphorus range in the basal portion of the YFEL in 123 day old vegetatively growing plants for predicting deficiency after a further 6 weeks growth was 0.07- 0.10% P.

The field experiment was set up with four rates of nitrogen and four rates of phosphorus in a factorial combination on a sandy soil to confirm the glasshouse obtained critical concentration ranges. All plants that survived had adequate supplies of nitrogen and phosphorus, and nitrogen and phosphorus concentrations in 170 day old vegetative plants in the field were higher than the critical concentration ranges established for deficiency in the glasshouse.

Item Type: Thesis (Masters by Research)
Murdoch Affiliation: School of Biological and Environmental Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Dell, Bernard and Bell, Richard
URI: http://researchrepository.murdoch.edu.au/id/eprint/51914
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