Response of Leucadendron ‘Safari Sunset’ to irrigation and fertilisation levels

Leucadendron ‘Safari Sunset’ is the most important cultivar in the Protea industry worldwide.The commercial product consists of long branches that terminate in a female inflorescence (“head”) surrounded by large, deep-wine-red leaves. The objectives of the present study were to assess the response of ‘Safari Sunset” plants to different levels of deficit irrigation and to various fertilisation strategies [e.g., constant concentration (fertilisation doses decreased or increased as irrigation rates decreased or increased, respectively), and constant quantity (nutrient concentration decreased or increased as irrigation rates increased or decreased, respectively)]. The impact of irrigation treatment on soil water content was apparent, and deficit irrigation significantly increased soil water tension, especially in soil layers below 20 cm, and diminished the volume of soil that was suitable for root development.The horizontal extent of the root volume followed the wetted zone and was almost congruent with the spatial distribution of water content. The majority of the root system was located in the 0 – 60 cm layer, but the layer 25 – 45 cm below the plant had the lowest water content indicating that the main zone in terms of active water uptake was situated within these limits. Irrigation rate had a dominant influence on biomass production, and a significant linear regression was obtained between plant fresh weight (FW) and soil water content. Linear regression analysis indicated that 95% of FW variation could be attributed to differences in soil water content. Deficit irrigation management diminished head dimensions and, consequently, reduced the commercial quality of ‘Safari Sunset’ plants. However, non-water-stress treatments induced excessive vegetative growth, mainly in the form of too-long branches, and an important part of the biomass produced was redundant. In the case of water scarcity and the application of deficit irrigation treatments, constant nutrient concentration should be applied.