ENVIRONMENTAL IMPACTS OF NITROGEN CONCENTRATION OF TOMATO AND PEPPER SEEDLING'S NUTRIENT SOLUTION

The research was aimed to estimate the influence of the major nutrient elements; nitrogen, phosphate and potash, on the growth rate of tomato and pepper seedlings, as also the environmental impacts of N concentration of the nutrient solution. The nitrogen concentration, namely 25, 50, 75 and 100 ppm, were considered as main factors, while phosphate and potash were at the following respective ratios (N:P:K); 1:0,4:1,2 and 1:0,6:1,8. N absorbed by plants was analysed and NRE was calculated. The increase of nitrogen concentration, from 25 to 100 ppm is followed by an progressive increase of the dry weight of both species; tomatoes and pepper. The gradual nitrogen increase was accompanied by a steady decrease of root dry weight versus total plant dry weight, and shoot dry weight. Generally speaking, top and root N concentration increased with increasing N solution concentration. Top and root N concentration of pepper seedlings were similar across all treatments, while on the contrary, considerable differences were found among the plant organs for tomato seedlings. The N content of leafs was much higher of that of stems and especially roots. NRE values were gradually decreased as long as N concentration increased from 25 ppm to 100 ppm. Considerable differences were found among the NRE values according to the growth stage of both crops. The increase of the plant root volume and leaf area index, each successive growth stage, should be the explanation for the gradual increase of N recovery efficiency of young plants. Consequently, the adjustment of N concentration at nutrient solution according to leaf area index seems to be the right method to reduce environmental N pollution.