MODELING GROWTH AND ION CONCENTRATION OF LILIUM IN RESPONSE TO NITROGEN:POTASSIUM:CALCIUM MIXTURE SOLUTIONS

Abstract

Nutrient solution composition plays an important role in root uptake rate due to interactions among nutrients and internal regulation. Studies to determine the optimum nutrient solution concentration are focused on individual ions, ignoring the adaptation mechanisms triggered by plants when growing in a varying external nutrient concentration. The objective of the present study was to determine the response in growth and tissue ion concentration of lilium cv. ‘Navona’ to nutrient mixtures of varying proportions of nitrogen (N), potassium (K+), and calcium (Ca2+) in solution using mixture experiments methodology in order to determine the optimum concentration. Bulbs of lilium were transplanted in plastic crates and drip-irrigated with the treatment solutions, which consisted of a mixture of N, K+, and Ca2+ whose total concentration was 340 mg L−1 and minimum concentrations of each ion was 34 mg L−1. Chlorophyll concentration (SPAD), shoot fresh weight (FW), leaf FW, and leaf area were measured 60 days after transplanting and ion analysis was performed on shoot tissues from selected treatments. Lilium exhibited a moderate demand for N and K+ (136–170 mg L−1 N and 116–136 mg L−1 K+) and a very low demand for Ca2+ (34–88 mg · L−1). This low demand may be due to the remobilization of the nutrients stored in the bulbs. Integrating the predictions of the models estimated to produce >90% of maximum growth, the optimum nutrient solution should contain Ca2+ at a concentration between 34 and 126 mg · L−1, K+ between 119 and 211 mg · L−1, and N between 92 mg · L−1 and 211 mg · L−1. Increasing external N concentration affected internal N concentration but not internal K+ or Ca2+ concentrations, despite that the increase in external N was associated with a decrease in external K+ and Ca2+. Similar trends were observed for external K+ and Ca2+ concentration. In conclusion, lilium was able to maintain a relatively constant K+ and Ca2+ concentration regardless of the lower concentration in the nutrient solution when N was increased (similar response was observed for K+ and Ca2+) and it has a low Ca2+ demand and moderate N and K+ supply.