Abstract
Orchid fertilization is fundamental for a satisfactory plant growth and development for commercial orchid production as well as in collections. Mineral and/or organic sources can be used for fertilization. The objective of this study was to evaluate the effect of the use of organic and/or mineral fertilizers on the nutrition and growth of orchid (Laelia purpurata 'werkhanserii' x L. lobata 'Jeni') seedlings in greenhouse. The following fertilizers were tested: an NPK fertilizer + micronutrients; a Ca source in the form of calcium nitrate; two organic fertilizers, one prepared with a mixture of bone meal, castor meal and ash, and a similar commercial fertilizer. The organic fertilizers were distributed on the surface of the pots every two months and the minerals were applied weekly to the substrate in 25 mL aliquots of a solution containing 1 g L-1 of the respective fertilizer. The plant response to the application of mineral together with organic fertilizer was better, with higher dry matter production than by the isolated application of each fertilizer (organic or mineral). The treatments with calcium nitrate + NPK fertilizer did not differ significantly from the use of NPK fertilizer, probably due to the S deficiency detected in a mineral analysis of the tissues. Commercial organic fertilizer had a very elevated B level, leading to toxicity symptoms, reduced growth and necrotized tips of the older leaves in all fertilized treatments.
Highlights
Orchids were not fertilized since it was believed that nutrients in the cultivation substrate were sufficient to maintain plant growth and development
Organic fertilizers were applied over the pot surface every two months and the mineral fertilizers were applied via aqueous solutions containing 1 g L-1 of fertilizer; the combinations or organic and mineral fertilizers were applied considering the intervals for each source of fertilizer
Excess shoots, deformed leaves and a darker green color were observed on plants treated with commercial organic fertilizer (CO) than in absence thereof
Summary
Orchids were not fertilized since it was believed that nutrients in the cultivation substrate were sufficient to maintain plant growth and development. As the level of technology applied increases, the risk of plant losses increase as well. This shows that there are limits for nutrient applications, with excellent results at adequate rates and the possibility of death due to nutrient toxicity and/or salinity when nutrients are supplied in excess (Novais & Rodrigues, 2004). Research results show that concentrations between 1 and 2 g L-1 of water-soluble fertilizer, applied weekly by fertilization, are satisfactory for plant growth and development (Wang & Gregg, 1994; Wang, 1996; Amberger-Ochsenbauer, 1997; Wang, 2000)
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