ASHS 2015 Annual Conference

The influence of nitrogen (N) and phosphorus (P) fertigation rates on plant growth and uptake of essential nutrients was evaluated in container-grown Iris germanica 'Immortality'. Factorial combinations of three N (5, 10, or 15 mM) rates and three P (5, 10, or 15 mM) rates were applied to iris plants twice per week from March to September in 2013. Plant height and leaf SPAD data were collected during the growing season. Plants were harvested in December to measure dry weight (DW) and analyze essential mineral elements concentration. Increasing N rates increased plant height, leaf SPAD, tissue dry weight and uptake of many essential elements potassium (K), calcium (Ca) and iron (Fe). P rates did not affect plant height or DW and only increased leaf SPAD in October. Increasing P rates increased concentration of P in leaves and roots and decreased boron (B) concentration in the leaves but did not influence net uptake of other nutrients. Concentrations of N, K, Ca, magnesium (Mg) and zinc (Zn) decreased in plant tissue in order of leaf>rhizome>root regardless the treatment. K was the only macro-element to have higher concentrations in roots than rhizomes. The average N:P ratio ranged from 4.7 to 7.5, 2.4 to 4 and 6 to 8.7 in leaves, roots and rhizomes, respectively. Compared to the common recommended threshold N: P ratio of 16:1, plants in this study may be N limited; however, P supply was sufficient, even at 5 mM P application.