415 Fertilizer Source and Medium Composition Affect Growth of Moth Orchid

Abstract

Vegetatively propagated Phalaenopsis Atien Kaala `TSC 22' plants 10 cm in leaf spread were potted in a medium that consisted of either 100% fine grade Douglas fir bark or a mixture of 70% fir bark and 30% sphagnum peat. Plants were fertigated at each irrigation with 10N-13.1P-16.6K (10-30-20), 20N-2.2P-15.8K (20-5-19), 20N-8.6P-16.6K (20-20-20), or a 2N-0.4P-1.7K (2-1-2) liquid fertilizer at a common N rate of 200 mg•L-1. After 1 year in a greenhouse, plants grown in the bark/peat medium produced more leaves and had heavier fresh weights and larger total leaf areas than those in 100% bark. In the bark medium, the 20N-2.2P-15.8K fertilizer resulted in best plants, despite its low P concentration (22 mg•L-1). When grown in bark/peat, the two fertilizers (20N-2.2P-15.8K and 20N-8.6P-16.6K) containing urea as part of their N source (10% and 52%, respectively) resulted in plants with 40% to 50% heavier shoot fresh weight and 40% larger leaf area than the other fertilizers. With any given fertilizer, plants had similar root weights in both media. Media and fertilizers had limited or no effect on the concentrations of minerals in the second mature acropital leaves except P, the concentration of which nearly doubled in leaves of plants grown in 100% bark. Water extracts from the bark/peat medium had lower pH, higher EC, and elevated levels of NH4-N, Ca, Fe, Na, Cl, B, and Al than those from 100% bark. Exacts from the bark medium did not have detectable levels of NO3-N, whereas extracts from the bark/peat medium all had similar levels of NO3-N, regardless of which fertilizer was applied.