International Water & Irrigation

39 Introduction The investigation of the nutrient requirements of a specific species has always been an important vehicle for optimizing nutrient management and reducing environmental contamination. Optimum nutrient applications for a species are often only valid under a certain set of growing conditions, resulting in a certain nutrient deficiency in the substrate to plant root systems. Given sufficient N supply, N uptake was considered to be subject to a plant’s internal regulation depending on growth rate, meaning that determination of optimum N rate should always be based on both substrate availability of the nutrient (N supply) and crop growth (N demand). Fertilizer application rates are commonly determined in nursery production based on the assumption that water availability does not limit nutrient uptake, and that container capacity should be maintained to promote plant growth and nutrient uptake. In recent years it has been increasingly deemed impractical to maintain container capacity in production. Nutrient availability has been shown to decline with low soil water content, which becomes a limiting factor for nutrients to become soluble and be delivered to root surface. The presence of a dry substrate can further hamper nutrient uptake impairing root growth, especially in a dry climate. Soil moisture conditions can be altered through altering irrigation frequency, requiring the influence of irrigation frequency on plant growth and nutrient uptake to be further investigated. Traditionally, when plants are grown in plastic containers, evaporative loss of water is mainly through the substrate surface rather than the container sidewall because plastic containers are impervious to water. Use of biodegradable containers as a sustainable alternative to plastic containers can alter water consumption characteristics of container-grown plants constructed with materials such as peat, wood fibre, straw, or paper are highly porous and tend to require more frequent irrigation requiring larger irrigation doses than traditional plastic containers. With increasing water loss between irrigation events, some biocontainers produced smaller plants while sidewall water loss from biocontainers is recognized to reduce substrate temperature. Growth response of azaleas flowers under different N fertilization levels and irrigation frequencies when grown in biocontainers compared with plastic containers has not been determined. Taking into account that the container used to grow nursery plants may have considerable influence on plant water consumption characteristics, container choice may alter the irrigation requirement and nutrient uptake of a given species. To understand more about the phenomenon a study was carried out: I) Investigate the influence of increased irrigation fre- quency on growth and N uptake of Azalea Chiffon flow- ers. II) Compare growth response of plants grown in a black plastic container with a biocontainer made from recy- cled paper. III) Determine the optimum N fertilization rate based on ir- rigation frequency and container type. The purpose of the study will provide a valuable reference for the fertilization and irrigation requirements of azalea ‘Chiffon’, a dwarf, slow-growing cultivar. The effects of Irrigation Frequency, Nitrogen Intake and Container Type on Plant Growth of Azalea ‘Chiffon’ flowers Optimum nutrient applications for a species are often only valid under a certain set of growing conditions, resulting in a certain nutrient deficiency in the substrate to plant root systems