Effects of nitrogen concentration in hydroponics on growth and development of tomato and spectral characteristics of leaf in greenhouse

The effects of different nitrogen concentrations of nutrient solution on growth and development of tomato and spectral characteristics of leaves were studied in hydroponics in asymmetrical multi-span greenhouse. The results show that leaf area index(LAI), plant height, number of leaves, number of trusses and yield of tomato and absorbance of leaves are improved with the increase of nitrogen concentration of nutrient solution within a certain limit of 0—15mmol/L, which indicates that nitrogen fertilization can promote growth and development of tomato plant. But growth and development of tomato plant is decreased when nitrogen concentration of nutrient solution is high. The highest LAI in the treatment of N15 is about 3.0, while those in the other treatments are lower in the whole growth period. Numbers of leaves and trusses in the treatment of N15 are the biggest among the four treatments, 26.7 and 7.0, respectively. There is significant correlation between tomato yield and nitrogen concentration in the six treatments. The yield is the highest under the treatment of N15 and is the lowest under the treatment of N5. Some spectral wave lengths which related to chlorophyll are extracted from spectral characteristics of leaves. The optimal nitrogen concentration of nutrient solution for tomato in the experiment is 15 mmol/L in hydroponics.