Fertilizer source and medium composition affect vegetative growth and mineral nutrition of a hybrid moth orchid

Abstract

Research was conducted to investigate the interaction of water-soluble fertilizer and medium composition on vegetative growth and the concentration of mineral nutrients in media and in leaves of a hybrid moth orchid (Phalaenopsis Blume.). The vegetatively propagated 'TSC 22' clone of the hybrid Phalaenopsis Atien Kaala plants 15 cm in leaf spread were potted in a medium consisting of either 100% fine grade douglas fir [Pseudotsuga menziesii (Mirb.) Franco] bark or a mixture of 7 fir bark: 3 sphagnum peat (by volume). Plants were fertigated at each irrigation with a soluble 10N-13.1P-16.6K, 20N-2.2P-15.8K, or 20N-8.6P-16.6K fertilizer, or a 2N-0.4P-1.7K 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, greater fresh weights (FW), and larger total leaf areas than those in 100% bark. In the bark medium, the 20N-2.2P-15.8K fertilizer resulted in plants of the highest quality, 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 FW and 40 % larger leaf area than the other fertilizers without urea. With any given fertilizer, plants had similar root FW in both media. Media and fertilizers had limited or no effect on the concentrations of mineral nutrients in the second mature acropetal leaves, except P, which nearly doubled in leaves of plants grown in 100% bark. High leaf Mg concentration was associated with low Ca. Water extracts from the bark-peat medium had lower pH, higher electrical conductivity, and much higher levels of NH4-N, Ca, Fe, Na, Cl, B, and Al than those from 100% bark. Extracts from the bark medium did not have detectable levels of NO3-N, whereas extracts from the bark-peat medium all had similar levels of NH4-N, regardless of which fertilizer was applied. Levels of P and K were not different between the two media.