Plants, whether grown in field or in pots, take their nutrition from inorganic minerals. Plant nutrition, therefore, takes into account all inter-relationships of mineral elements present in the soil or sod less media, their availability to the plant roots. Optimum nutrition involves a complex balance of essential elements and other beneficial elements required for optimum plant growth. This requirement varies according to plant species. Orchids are no exception. Orchids like any other plants require nitrogen; phosphor., potash and trace elements for healthy growth (Kong, 1979; Fitch, 1981). From experiences over the year, it is recognized that, in general, orchids grow satisfactorily when fed with a balanced fertilizer for about 10 months a year except the period when plants are in new growth. During the new growth period it is better to supply them with a nitrogen rich fertilizer. Some growers also shift to blossom booster fertilizer during the period before flower initiation. It is recommended to stick to one formula. Constant changes cause dangerous imbalances that seldom gives satisfactory results (Fanfani and Rossi, 1989). A fertilizer equally balanced in nitrogen (Inc overall growth), phosphorus (fair flower boosting) and potassium (for healthy roots), may be in a ratio 01 18.18:11 or 2010:20, dissolved in water at a dose of 1 g to 1 liter and applied once in a week Ira good choice. It is also goods flush the plants with thorough watering in between two fertilization, to avoid any risk of salt deposition. Fertilizer containing urea should be avoided cony case, as it needs to be broken down by specific soil microbes before it can become available to the plants. Fertilizer wash should not be recollected for use as it may spread diseases, if any. More dangerous is over fertigation which will lead to salt deposition in the pot. Salt deposition can be identified in the form of white crusts on the media and around the pot. Dieing of leaf tips is also an indication of salt deposition. Roots also turn black when they come into contact with the salts deposited in pot. Orchids have very low tolerance to excess salt (Papenhagen, 1980). If it is evident that plants am suffering from salt deposit Mn, then it is better to repot in a fresh pot and media. Washout all the salt deposits from root zone before repotting. Never fertilize a sick plant. If plants are not doing well, do not try to boost their growth by simply increasing the fertilizer dose. This will not help. Foliar application of nutrients in orchids whose effectiveness depend on the fact that whether orchid leaves uptake nutrients or not is a debatable issue. Boozing (1973) and Poole and Sheehan (1982) observed nutrient uptake by orchid leaves. However, the study by Benzing (1973) revealed that the rate of absorption by leaves was less than one-eighth of that absorbed by roots. Sinclair (1990) is also of the opinion that under natural conditions the absorption of water or nutrients by orchid leaves is rarely significant. Poole and Seeley (1978) reported in nutrient culture„ growth hybrid plants of Cymbalium and Phalaenapsis was optimal with 100 pm N, 50-100 pm K and 25 pm Mg. affleya did well with 50 pm of N, K and Mg. Cymbielium plants developed N deficiency when supplied with 50 pm N, Mg at 100 pm reduced growth. Many types of organic manures including dilute liquid form of old cow, sheep or fowl manure, dilute urine, one part in ten parts of water, water extracts of finely shredded fresh fish, groundnut cake - one kg of cake dissolved in 10 gallons water for rotting, the solution is sieved and used, were reported to be good for orchids (e.f.Bhattacharjee, 1995; Bose and Bhattacharjee, 1980). Bhattachatijee (1981) studied eftect of N, P. K at 0,500 and 1030 pm on Dendrobiton moschatum and concluded that increasing level of N markedly improved vegetative growth and flowering. Addition of P105 also influenced all vegetative and flower characters. Concentration of 500 pm of all the three nutrients was best. Abraham and Vatsala 0981) reported beer at strength of one quart in 10 gallons of water to be beneficial for orchids. Ohattachaijee et at (1980) observed chemical fertilizer mixture containing both macro and micronutrients to produce best response in Aerides multi/Inman and Dendrnblutn moseInthon. One per cent spray of cowdung or oil cake solution also improved growth and flowering in both the orchids. Significant improvement mike production of more number of inflorescences, number and size of flowers was reported in Aerides multifloruni due to application of 1000 pm each of N and Py spray. Prolongation of vase life was also reported with increase in doses of 1.20, and K20 (Bhattacharjee, 1932). Uptake of nitrate and ammonium by two terrestrials Brontheadin finlaysonia and Cyrnbidiunt sntense and an epiphyte Dendrobium no. 'White Fairy" was reported to linear in rate, with higher uptake rate for ammonium (Flew eta)., 1993). Uptake rates were considerably lower than most of the major crops. They suggested movement of ions across the transfer junction as the exoderrnis plays a major role in regulation of nutrient uptake by orchid root, Wang and Gregg (1994) recorded that regardless of medium increasing the fertilizer application from 0,25 to 1 .0 g/liter increased flower number, stalk diameter and length and leaf production following flowering in Phalaenapsis. Cymbidium sinense grown under defficient/low K conditions (0 or 0.1 mmol/litre) produced poor growth, few flowers and high incidence of brown spat disease (Cloenvorium orchieleorunt). At higher concentration 01K, photosynthesis and respiration rate increased and them was greater root activity, leaf growth was rapid, flower number increased and the incidence of brown spot decreased. A concentration of 5 mol K/liter was considered to be most suitable (Perot al., 1994). Growth of Phaleenopsis in sugarcane bagasse was reported lobe improved significantly by increasing the nitrogen dose from 70 to 200 pm and also by inclusion of 10-40% organic fertilizer (Wu et al, 1994). Gonzalez (1994), however, observed that application of compound NPK fertilizer generally reduced growth of C.attleya down= Tsai et aL (1996) reported that nutrient uptake rate in Cymbidiunt sinense was highest with 201015 NPK rate and with 05% organic fertilizer. Phalaenopsis plants provided with higher N rate, regardk,s of which fertilizer was used, produced snider leaf spread, more and longer leaves, and greater total leaf area. The ION 13.1 16.6 K fertilizer lowered the pH of medium, and medium EC was always higher with ION 13.1 P 16.6 K or ION : 8.7 P 20.8 K (Wang and Wang, 1996), Vi) eta). (1997) suggested do's and dusts for fertilizing orchids. They suggested nol to fertilize a dry plank not to apply strong dose as orchids prefer sneak solution of fertilizers frequently than higher doses less often, not to provide too much nitrogen during flowering as it is inhibiting, not to apply high nitrogen fertilizer on small seedlings as it leads to a weaker plant, and not to fertilize a sick plant. They recommended application of fertilizer by dissolving them in luke warm water, which should be poured through potting mix. fertigation should be done once a week while in active growth and once every other week when it is not in active growth. |
