Effects of Nitrogen Supply on Growth and Nutrient Status of Containerized Crape Myrtle

Abstract

Containerized crape myrtle (Lagerstroemia indica x fauriei ‘Tonto’) plants were grown over a 9-month period using complete nutrient solutions, except during overwintering, that differed in N concentration: 15, 30, 60, 120, 210, and 300 mg/liter. Plant shoot biomass, leaf area and canopy diameter increased with applied N concentrations ([N]a) up to 60 mg/liter, but higher levels caused significant depressions in all these parameters. Root biomass and plant height were depressed linearly with increases in [N]a. Regardless of final plant biomass, increases in [N]a significantly favored shoot over root growth, with ratios increasing from 1.9 to 5.4 for 15 to 300 mg/liter, respectively.Soluble salts in the medium, monitored via leachates, increased with N supply and were identified as a key factor involved in the yield reductions observed at the higher [N]a. Leaf N concentration increased with N supply, stabilizing at [N]a above 120 mg/liter; concentrations of 2.6–2.7% were associated with maximum growth. Calcium and iron concentrations in tissue followed the same response pattern as N, but sulfur (S) decreased significantly in an opposite pattern. Other nutrients did not respond to [N]a. Leaf tissue N:S ratios were more closely correlated with plant growth that either N or S alone, with maximum growth observed at a ratio of approximately 6:1. Higher N:S ratios produced sharp yield depressions.