Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2008
Publication Date: 9/1/2008
Citation: Scagel, C.F., Bi, G., Fuchigami, L., Regan, R. 2008. Nitrogen availability alters nutrient uptake and demand in deciduous and evergreen container-grown Rhododendron. Journal of Environmental Horticulture. 26(3):177-187.
Interpretive Summary: The influence of N-availability on uptake and demand for other nutrients by one-year-old rhododendron (Rhododendron ‘H-1 P.J.M’) and azalea (Rhododendron 'Cannon's Double') was evaluated from May to September. The estimated rates of nutrient uptake in relationship to N-availability will be useful in the development of fertilizer management strategies that strive to decrease fertilizer use by synchronizing the availability of nutrients with plant demand. The ratios of N to other nutrients in plants were determined to have potential usefulness in evaluating co-uptake of nutrients in relationship to N. Further research on using N-ratios for predictive purposes in nursery nutrient management could improve our understanding of the balance of nutrients required for optimum plant growth.
Technical Abstract: One-year-old rhododendron (Rhododendron 'H-1 P.J.M.') and azalea (Rhododendron 'Cannon's Double') were grown with (+N) or without (N-deficient) N from May to September to determine the effects of N-availability on uptake, demand, and allocation of other nutrients. A 7-fold increase in N uptake by rhododendron caused a 3 to 4-fold increase in the uptake rate of P, K, and S and ~2-fold increase in the uptake rate of Mg and Ca. A 6-fold increase in N uptake by azalea caused a 3 to 4-fold increase in the uptake rate of K, Mg, and Ca and ~3-fold increase in the uptake rate of P and S. This suggests that when altering nutrient management strategies to optimize N uptake, proportional changes in other nutrients may not be required. N-deficiency also caused deficiencies in P, K, S and Mn for rhododendron and P, K, S, Ca, and Mg for azalea. This suggests that N-deficiency decreased the plant’s ability to take up these nutrients; therefore, when altering nutrient management strategies to decrease N fertilizer use, the influence of lower N rates on the ability of plants to take up other nutrients should be considered. Ratios of N to P, K, S, B, and Fe (N-ratios) for both cultivars were similar when N was not limiting to growth, indicating that fertilizers with similar availability ratios for these elements in relationship to N could be used with both cultivars. Cultivars differed in N-ratios for Ca, Mg, Mn, and Zn, indicating that availability of these elements in fertilizer in relationship to N availability may need to be altered for optimal growth of each cultivar. For both cultivars leaf N/P over-estimated P uptake and stem N/P underestimated P uptake; however, N/P ratios based on both stems and leaves may be useful for evaluating co-uptake of P in relationship to N. Leaf N/K and N/Ca, and stem N/S for rhododendron varied little during the experiment, indicating these ratios may be useful for evaluating co-uptake of K, Ca, and S in relationship to N for rhododendron.