Abstract: The critical nitrogen concentration (Nc) is the minimum nitrogen concentration when the maximum biomass is obtained in a certain growth period. It is of great significance for real-time understanding of crop nitrogen nutrition status, improving crop quality and yield, and avoiding fertilizer waste. In order to study the nitrogen management rule of greenhouse tomato under high temperature stress and determine the critical nitrogen concentration (Nc), a comprehensive experiment of high temperature and nitrogen application rate was conducted in the Venlo greenhouse of Nanjing University of Information Technology. Four temperature levels (T1 (25℃/15℃, CK), T2 (30℃ /20℃), T3 (35℃ /25℃) and T4 (40℃ /30℃) were set up, namely, no nitrogen N1, 0.5 times recommended fertilization N2 (1.3g·plant−1), 0.75 times recommended fertilization N3 (1.95g·plant−1), normal recommended fertilization N4 (2.6g·plant−1, CK), 1.25 times recommended fertilization N5 (3.75g·plant−1). After the potted tomato plants began to absorb fertilizer, the high temperature test was carried out in the climate box with different temperature treatment. After 7 days of high temperature treatment, the tomato plants were moved to the Venlo type experimental greenhouse at normal temperature for continuous cultivation. From the second day, the plant biomass and nitrogen content of each organ were systematically measured by periodic destructive sampling. The results showed that the dry matter mass (DM) of tomato plants increased with the development of growth period under different high temperature nitrogen treatments, and the relationship between critical nitrogen concentration and aboveground biomass of greenhouse tomato was in accordance with power index：Nc=a·DM−b, among them, T1：Nc= 4.167DM−0.252；T2：Nc= 4.689DM−0.375；T3：Nc= 3.287DM−0.353；T4：Nc=3.812DM−0.403. With the aggravation of high temperature stress, the critical nitrogen concentration of tomato first increased and then decreased, the dry matter accumulation of low nitrogen treatment was higher than that of high nitrogen treatment; with the increase of nitrogen application rate, the plant nutrition index (NNI) under each temperature treatment increased, and with the extension of treatment time, the plant nutrient index showed a downward trend.

Key words: Tomato, High temperature, Critical nitrogen model, Nitrogen nutrition index, Nutrition diagnosis