Foliar application of silicon can be beneficial to orchid growth, but it may also impair growth depending on the source and solution concentration. Due to the lack of information on silicon toxicity in long-term orchid nutrition, experiment with two different orchid species, Phalaenopsis Golden Peoker and Dendrobium Valentine, were performed. The plants were grown in plastic trays with dry Sphagnum in a greenhouse, being fed the nutrient solution without silicon in the first six months. After that, the plants were transplanted to individual plastic vessels (0.9 L). The treatments followed a completely randomized design with a 5 × 3 factorial consisting of five Si concentrations (control, 14.3, 28.6, 42.9 and 57.2 mmol L −1) and three sources (monosilicic acid, potassium silicate, and potassium silicate and sodium silicate mixture), with five replicates. After 18 months of Si foliar application, the Si, C, N, P, K, Ca, Mg and S levels, lignin content and biometric variables were determined for both species. The application of 27 and 16 mmol L −1 Si (potassium silicate and monosilicic acid) resulted in the highest values for the evaluated biometric parameters for Phalaenopsis and Dendrobium, respectively. The results suggest that silicon foliar application affected nutrient absorption and green color index of Phalaenopsis and Dendrobium, and the lignin content of Phalaenopsis. Application of concentrations greater than 39 and 18 mmol L −1 Si over 18 months was toxic to Phalaenopsis and Dendrobium, respectively, since the orchid dry matter decreased by 10% (critical level due to toxicity). Applying increasing concentrations of Si sources decreased the C:N:P stoichiometric ratio of orchids.

IVCrescimento in vitro e aclimatização de Cattleya loddigesii Lindley (Orchidaceae) com carvão ativado sob dois espectros luminosos

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Phalaenopsis and Dendrobium do not grow and flower well with 100% ammonium (NH 4-N); and there are detailed studies on the effects of nitrate (NO 3-N) and ammonium ratios on the flowering, but no information about accumulation of other nutrients and the effects of ammonium toxicity on orchids. For this reason, two experiments were carried out with orchids: Phalaenopsis 'Golden Peoker' and Dendrobium 'Valentine'. Six months after acclimatization the plants were transplanted to individual plastic vessels and the treatments consisted of five ratios (%) of nitrate / ammonium (0/100, 25/75, 50/50, 75/25, 100/0). The sources of NO 3-N and NH 4-N were calcium nitrate and ammonium sulfate, respectively. After 12 months treatment, when the plants were beginning to issuance of flower stem, the accumulation of: N, P, K, Ca and Mg in the shoot and biometric variables were evaluated for both species. The NH 4-N ratio of 40% and 50% of the total nitrogen benefited the growth of Phalaenopsis and Dendrobium, respectively. The application of higher proportions of ammonium resulted in decreased N, K, Ca and Mg absorption, index of green color and increased leakage of electrolytes in Phalaenopsis and Dendrobium. NH 4-N proportions greater than 75% for 12 months caused toxicity in Phalaenopsis and Dendrobium.

Dendrobium nobile Lindl. is one of the most cultivated and distributed orchids around the world; however, information on its nutrition is scarce. Our objective was to study the plant development and nutrient accumulation in plants of D. nobile weekly fertilized with 100 mL Sarruge nutrient solution at 75% concentration. One plant per replication was randomly collected every month, along 12 months, totaling four plants. Dry matter (DM) and nutrient accumulation were determined for the different plant parts. Plants had already accumulated nearly 50% of total DM up to the flowering stage (240 days after first fertilization, DAFF). Order and amount of accumulated nutrients, at 360 DAFF, was, in mg per plant: K (701.07) > N (339.44) > Ca (289.03) > Mg (135.44) > P (118.83) > S (23.56); in mg per plant, it was Fe (14,122.35) > Zn (5,277.82) > Mn (3,216.87) > B (1,253.02) > Cu (271.25).