A range of Proteaceous shrubs and other nursery plants were grown in containers with soilless media and various N levels. Plants demonstrated a range of responsiveness. Supplying soilless media with Osmocote (26% N) and other short term fertilisers proved to be a satisfactory method of studying the comparative nutrition of a wide range of container grown nursery plants using factorial experiments incorporating N, P, K and lime. Nutrient response surfaces were obtained using a central composite incomplete block design. Most Proteaceous shrubs were intolerant of high P levels due to excessive luxury consumption resulting in toxic foliar nutrient levels, especially in the presence of high N. Phosphorus sensitivity in plants appeared to correspond with the soil nutrient levels in their native habitat. This applied to species studied in the 2 main sub-families in the Proteaceae while similar findings were indicated for other Australian genera. A range of optimum N requirements in the Proteaceae was found – lowest needs for Protea which also had the greatest tolerance of very low fertiliser additions, compared to Grevillea robusta with much higher N requirements and strong foliage growth inhibition if nutrient levels are very low. Proteoid root growth on Grevillea rosmarinifolia only occurred at low nutrient levels and was not required for satisfactory foliage growth of container grown plants. Pot plants and seedlings, especially tomato, responded strongly to N and often there were positive NK interactions influencing foliage growth. Lime requirements were studied and in erica increasing lime rates depressed foliage growth. Comparative nutrition studies indicate that general or broad spectrum container media may be unsuitable for some groups of nursery plants and that they could be replaced by potting mixes designed to meet the widely differing needs of the species often grown. The number of specialist mixes would depend on the range of plants and be governed by management considerations.

Doctor of Philosophy / Department of Horticulture, Forestry, and Recreation Resources / Kimberly A. Williams / The use of calcined clays contributes properties of nutrient and water retention to soilless root media, which varies greatly depending on the parent clay and calcining treatment. This research characterized phosphate (PO[subscript]4) sorption of various calcined clay products, including low volatile and regular volatile material (LVM and RVM) 2:1 Attasorb clays (Engelhard Corp.), 2:1 Terra Green LVM clays (Oil-Dri Co.), and Turface (Profile Products LLC) at various particle sizes; 1:1 kaolin clays (Thiele Kaolin Co.) in powder form, and diatomaceous earth (Diatomite, Eagle Picher Minerals, Inc.). Three of the calcined materials, Terra Green montmorillonite and Attasorb attapulgite (which had high PO[subscript]4-sorption based on isotherms), and diatomaceous earth (which had negligible PO[subscript]4-sorption) were evaluated as components of soilless root media in two separate greenhouse experiments. The effect of the calcined materials, rate of incorporation (0%, 5%, 10% and 20% by volume in a mix with peat and perlite), and PO[subscript]4-P application rate (0, 5, 15, 45 mg.L[superscript]-1 PO[subscript]4-P) on plant growth, effluent P content and water use were determined during production and post-production of Impatiens wallerana Hook f. 'Tempo Rose'. The calcined materials varied in their ability to adsorb PO[subscript]4-P and generally yielded L-type isotherms. Laboratory results indicated potential for substantive P retention by several of the calcined materials when used in container production. For most materials, PO[subscript]4-P sorption did not show pronounced pH dependence. During production and post-production, the test materials not only improved PO[subscript]4-P retention but also water retention and water use efficiency while still maintaining optimal physical properties at incorporation rates of 5 to 10%. Diatomaceous earth resulted in PO[subscript]4-P retention not significantly different from the calcined clays.