Compared with fruit and vegetable crops, the effects of potassium (K) on growth and performance of ornamental and floral crops have not been studied as extensively. K deficiency is a widespread disorder on many palm species worldwide (Chase and Broschat, 1991) that can lead to the death of the plant if supplemental K is not applied (Broschat, 1990).
In field studies, flower production of Anthurium andraeanum Linden. (Higaki et al., 1992) and Gerbera jamesonii H. Bolus ex Hook.f. (Dufault et al., 1990) increased when K was at 375 and 110 to 220 kg·ha−1, respectively, compared with lower rates. In a greenhouse study, increasing K concentration from 0.25 to 10 meq·L−1 (10 to 390 mg·L−1) in the recirculating nutrient solution resulted in more flowers, longer stem, and whole-plant fresh weight of Rosa hybrida ‘Forever Yours’ (Woodson and Boodley, 1982). Shoot dry weight and leaf area of Salvia splendens F. Sellow ‘Bonnfire’ increased as K concentration increased from 25 to 300 mg·L−1 (Eakes et al., 1991). The tropical foliage species Aglaonema commutatum Schott, however, did not respond to increased K from 80 to 320 mg per 15-cm pot per month (Poole and Conover, 1977).
Phalaenopsis Blume. hybrids are the most popular pot orchids on the market around the world. Individual flowers of these orchids often last 3 to 4 months (Wang, 1997, 2000). Their relatively rapid growth and short juvenile period (Lee, 1991) are advantageous for breeders to improve this crop by crossbreeding and cloning. Several studies found that Phalaenopsis plants require high nutrient concentrations for optimal growth under warm environmental conditions (Lee and Lin, 1988; Wang, 1996; Wang and Gregg, 1994).
Leaves of healthy Phalaenopsis plants may remain on the plant for 2 or more years and contain 3% to 8% K on a dry-weight basis (Lee, 1988; Wang, 1998; Wang and Konow, 2002). In recent years, a physiological disorder has been observed on Phalaenopsis leaves. The affected plants had irregular yellowish areas on the second or third basipetal leaves (Chen, 2001; Lee, 2001; Lee and Lee, 2000). Symptoms of this disorder became much more severe after vegetative plants have been induced to initiate the flowering process by exposing them to cool air. The yellowed leaf tissues were found to have extremely low levels of K (0.40% to 0.64%) (Lee, 2001). No controlled studies have been conducted to quantify Phalaenopsis K requirements and to characterize the specific symptoms of K deficiency.
As a result of the long production time from seed, millions of Phalaenopsis plants of varying sizes are imported to the United States each year from overseas suppliers. Although nearly all overseas Phalaenopsis suppliers grow this crop in straight sphagnum moss (moss), most growers in the United States produce this orchid in media largely made of ground douglas fir [Pseudotsuga menziesii (Mirb.) Franco] bark. Because it is obvious that these two materials have markedly diverse water retention characteristics, Phalaenopsis grown in these media may have different requirements for K concentration in the nutrient solution being applied.
The objectives of this study were 1) to determine the growth and flowering of Phalaenopsis in response to a wide range of K concentrations when grown in two media drastically different in water and nutrient retention characteristics and 2) to characterize the K deficiency symptoms.
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