Nutrient Management in Reblooming Iris 'Immortality'
AdvisorHarkess, Richard L.
CommitteeBlythe, Eugene K.
Crouse, Karl K.
Denny, Geoffrey C.
For its fragrance, showy display and multi-colors, tall bearded (TB) iris (Iris germanica L.) has great potential as a specialty cut flower. This study was conducted to investigate the optimum nutrient management, especially nitrogen (N), of reblooming TB iris 'Immortality'. The objectives were to investigate the effects of N rate and form and phosphorus (P) rate on growth, flowering, and nutrient uptake, and to assess seasonal changes in the composition of nitrogenous compounds and carbohydrates. In general, greater N rates increased plant height, leaf SPAD reading, the number of inflorescence stems, plant dry weight, plant N content, and uptake of other nutrients. Spring flowering was more dependent on N stored from the previous year. Second bloom was largely influenced by N rate in the year of flowering. In spring, N uptake efficiency quadratically related with increasing N rate and was highest in the 10 mM N treatment. Percentage of tissue N derived from spring fertilizer decreased with increasing N rate applied from previous year. In comparison with N rates, P rates did not affect most of growth and flowering performances, but had slight influences on concentration of few nutrients (such as P, potassium, and boron). Considering N:P ratios in plant tissues in this study were low, these results imply 5 mM P rate, the lowest P rate tested in this study, was sufficient for growth and development of reblooming TB iris. NH4:NO3 ratios did not affect plant height, flowering, dry weight, and N uptake, suggesting TB iris may not have preference for either ammonium or nitrate N. Higher NH4:NO3 ratios increased leachate pH, which might influence uptake of iron, manganese, and zinc. Nitrogen and carbon were predominately allocated to rhizomes in December and to leaves in May, suggesting a process of nutrient storage and remobilization happened in TB iris with seasonal changes. Concentration of starch, sucrose, glucose, and fructose showed seasonal changes, while concentration of free amino acids did not. Starch was the major form of storage carbohydrates in December. Glutamate, alanine, aspartate, serine, and tyrosine were main constituents among free amino acids.