NITROGEN EFFECTS ON THE RELATIVE GROWTH RATE AND ITS COMPONENTS OF PEPPER (CAPSICUM ANNUUM) AND EGGPLANT (SOLANUM MELONGENA) SEEDLINGS

The influence of the major nutrient elements: nitrogen, phosphate and potash, and their ratios of the nutrient solutions on the growth rate of pepper and eggplant seedlings were estimated in several experiments conducted in plastic greenhouses during 2003 and 2004. Differentiated nutrient solutions were applied based in a split plot design. Two sets of nitrogen concentration; 25, 50, 75 and 100 ppm, and 100, 200 and 400 ppm were applied in different experiments, while phosphate and potash were in the following respective ratios (N:P:K): 1:0,4:1,2; 1:0,6:1,8 and 1:1,2:2,4. The necessary microelements were also added to the nutrient solutions and equal quantities of 20–50 ml/plant were daily supplied. Plant dry matter content and leaf area were successfully measured and relative growth rate (RGR) and its components; net assimilation rate (NAR) and leaf area rate (LAR) were calculated. Significant differences of RGR were founded due to the N concentration at the nutrient solution. Statistically significant differences were found for both RGR components; NAR and LAR, at low nitrogen concentration (25 to 100 ppm). Consequently, at low concentration of nutrient solution any increase of N concentration, has increased the seedling growth rate by both; faster expansion of the plant leaf area (LAR) and higher physiological plant productivity (NAR). Meantime, at higher nitrogen concentration (100 to 400 ppm), increased values of RGR were achieved due to higher values of leaf area ratio (LAR), while the estimated values of net assimilation ratio (NAR) were mostly remained unchanged. RGR was not significantly effected by NPK ratio, neither its components; NAR and LAR, but meantime a strong effect on the LAR components, SLA and LWR was found.