EFFECT OF NPK LEVELS ON GROWTH AND BULB QUALITY OF SOME GEOPHYTES IN SUBSTRATE CULTURE

Freesia corms were grown in substrate culture using sand: rice huskcharcoal: coconut fiber at the ratio of 1:1:1. The optimum levels of NPK in the nutrient solution were studied using different combinations of nitrogen at 100 and 200 mg/L, phosphorus at 50 and 100 mg/L combined with potassium at 100, 200 and 300 mg/L. The results showed that the minimum level of NPK at 100:50:200 mg/L was good enough for growing Freesia in substrate culture. Tubers of Gloriosa rothschildiana (10-25 g FW) were grown in substrate culture. The -N, -P, -K, -Mg and -Ca treatments compared with complete nutrient formula were supplied to the tubers. The results showed that nutrient deficiency reduced plant height, number of nodes, tuber fresh weight and tuber length. The optimum level of NPK was further studied by supplying tubers with different combinations of nitrogen at 100, 200 and 300 mg/L , phosphorus at 50 and 100 mg/L combined with potassium at 100, 200 and 300 mg/L. The results showed that the NPK combination at 200:100:200 mg/L was optimal for growing Gloriosa rothschildiana in substrate culture. INTRODUCTION Hydroponic systems offer the opportunity to provide nutrients in a range adequate to plant growth and demand, whereas in conventional cultivation nutrient supply depends also on the nutrient status of the soil (Schnitzler and Gruda, 2002). Freesia in substrate culture on rolling benches shows the best prospects for production. Although investment is rather high, it is paid back by the increased utilization of space. Because heating and cooling of the substrate are of great importance for a good yield, substrate beds are also used. In this way, the substrate temperature can be controlled better and with less energy than in soil (van Os et al., 2002). Gloriosa in substrate culture is good for easy harvest of tubers. Supply of nutrients is of great importance for the quality of horticultural products grown in this system. However, the danger of nutritional disorders in hydroponics compared with conventional cultivation methods is higher because the buffering capacity of substrate or nutrient solutions is lacking entirely or is significantly reduced (Schnitzler and Gruda, 2002). Usually, liquid fertilizers, such as 20-20-20 (N-P2O5-K2O) are frequently used for supplementation by addition to the irrigation water for growing plants in an organic soilless mix. The concentration is varied depending on the crop requirement. A common recommendation is a concentration of nitrogen between 50 and 100 mg/L. However, some crops are more sensitive to particular elements than others. Therefore, one nutrient formula will work well for one crop but poorly for others. The ratio of the concentration of elements in the nutrient solution can have a marked effect on plant absorption (Jones, 1997). This research aimed to investigate the optimum concentration of N, P and K for Freesia and Gloriosa and the nutrient deficiency in G. rothschildiana grown in substrate culture. Proc. X IS on Flower Bulbs and Herbaceous Perennials Eds.: J.E. van den Ende et al. Acta Hort. 886, ISHS 2011 214 MATERIALS AND METHODS Experiment 1 Effect of NPK on Growth and Development of Freesia ‘Oberon’ Freesia ‘Oberon’ corms were grown in pots using substrate media that comprised of sand:rice husk-charcoal:coconut fiber at a ratio of 1:1:1. Mother corms, used in this experiment, contained 27.72 mg g DW of N, 6.06 mg g DW of P and 33.31 mg g DW of K. After the shoot emergence, each pot was supplied with 50 ml L of nutrient solution, three times a week for 20 weeks. The nutrient solution comprised of different combinations of N (100 and 200 mg L), P (50 and 100 mg L) and K (100, 200 and 300 mg L). Each treatment also contained Ca 91.28, Mg 24.65, SO4 158.22, B 0.22, Mn 0.54, Zn 0.26, Fe 0.45, Mo 0.04 and Cu 0.03 mg L. The experimental design was factorials in completely randomized design with 2×2×3 factorials and 5 replications per treatment (5 plants per replication). Plant height, number of leaves per plant were measured every two weeks, flower and corm quality were measured at flowering and harvest, respectively. Experiment 2 Effect of NPK on Growth and Development of Gloriosa rothschildiana 1. Experiment 2.1 NPK Deficiency. Tubers of Gloriosa rothschildiana (10-25 g FW) were grown in media comprising sand:rice-husk charcoal (1:1). The -N, -P, -K, -Mg and -Ca solutions were supplied to the media compared with the complete Hoagland solution (Hoagland and Arnon, 1950). Experimental design was completely randomized design with 10 replications/treatment. Plant height, number of nodes and tuber quality were measured. 2. Experiment 2.2 Optimum Levels of NPK in Nutrient Solution for Gloriosa rothschildiana. Tubers with 5-10 g FW were planted in sand:rice husk-charcoal:coconut fiber (1:1:1). After shoot emergence, plants were supplied with different nutrient solutions comprising the combinations of N (100, 200 and 300 mg L), P (50 and 100 mg L) and K (100, 200 and 300 mg L). Each treatment also contained Ca 91.28, Mg 24.65, SO4 158.22, B 0.22, Mn 0.54, Zn 0.26, Fe 0.45, Mo 0.04 and Cu 0.03 mg L. Experimental design was factorials in completely randomized design with 3×2×3 factorials and 10 replications per treatment (3 plants per replication). Data measurement was done as in experiment 2.1.