Effects of different LED light and nitrogen application on growth of lettuce plants and leaf nitrate content

Abstract

Leaf nitrate contents of vegetables and other plants vary. The quantity of light and nitrogen in the environment is one of the most important factors affecting the nitrate metabolism of plant leaves. For this reason, 3 different doses of nitrogen (50, 100 and 150 ppm) were applied to the lettuce plant grown in soilless culture in the greenhouse during the spring period and light-emitting diode (LED) lights (red, purple, blue, and yellow and their combinations) were applied on the plant. Light applications were operated in the automatic system between 8 am and 24 pm. The light intensity on the plant was measured with a light meter at 10 a.m. and 3 p.m. The effects of applications of different LED lights and nitrogen doses on the marketable plant head weight, plant diameter, and chlorophyll ratio of the lettuce plant were found to be statistically significant, but its effect on Brix-Water Soluble Dry Matter (WSDM), pH, and titrable acid ratios were not found statistically significant. Considering the averages, while the head weight was 435 g/piece in the 50 ppm N application, it was 832 g/piece in the 150 ppm N application. Red LED light application, which is one of the lighting applications, provides an increase in efficiency compared to the control. While the leaf nitrate content of lettuce was 1213.2 ppm in the 50 ppm N application, considering the averages, it was measured as 1935.4 ppm in the 150 ppm application. The results show that the preference of dose of N to be applied in the lettuce plant is significant in the relationship between yield and nitrate, and plant growth increases with additional light application.