Low-level Nitrogen Fertilization Improved Root Growth Components and Quality of Containerized Artichoke Transplants

Stand establishment of artichoke transplants during late summer or early fall is challenging in hot and semi-arid growing regions of the southern United States. A repeated greenhouse experiment evaluated artichoke [Cynara cardunculus L. var. scolymus (L.) Fiori cv. Green Globe Improved] transplants at two nitrogen (N) levels (75 and 150 mg·L^-1) and with two irrigation systems (flotation and overhead). Transplants were grown for 8 weeks, with fertigation applied once a week. Roots and shoot morpho-physiological measurements were taken at 4 and 7 weeks after seeding.  Transplants grown with 75 mg·L^-1 had greater root surface area, root length, root branching, and thinner root diameter than those fertigated with 150 mg·L^-1.  Conversely, transplants grown with 150 mg·L^-1 significantly increased total N content in roots and shoots, chlorophyll content (SPAD), and leaf photosynthesis. As a result, these transplants exhibited greater shoot length and leaf area than those grown with 75 mg·L^-1, these responses were more pronounced 7 weeks after seeding.  Root and shoot length and surface area from overhead and flotation irrigation systems were statistically similar. However, 7 weeks after seeding, transplants under overhead irrigation had slightly greater stem diameter (~10%), shoot and root total N (~10%), and photosynthesis (~10%) than those grown with the flotation system. Overall, applying low level of N (75 mg·L^-1 ppm) with either flotation or overhead irrigation systems can improve the transplant root system and produce shorter and more rigid seedlings, improving the ability to withstand pulling from the trays and potentially the tolerance to withstand transplant shock in the field.