Abstract: 【【Objective】The aim of this study was to clarify the effect of nitrogen fertilizer on root growth and yield of peanut varieties differing in drought tolerance under different water conditions and to provide a theoretical basis for the management of water and fertilizer in peanut.【Method】The drought-resistant variety Huayu 22 and drought-sensitive variety Huayu 23 were planted in the anti-canopy tanks using the soil column. The soil water condition had two levels: well-watered conditions (W1) and medium drought (W0) (corresponding soil water contents are 70%-75% and 45%-50% of field capacity, respectively). The nitrogen had three levels: no nitrogen (N0), moderate nitrogen (N1, 90 kg×hm^-2) and high nitrogen ((N2, 180 kg×hm^-2). The root morphological characters, root exudates and yield of peanut were investigated under different treatments. Root samples were collected from 0-20 cm, 20-40 cm and below 40 cm soil layers, respectively. Root length, root surface area and volume were determined by a scanner and analyzed by WinRhizo Pro Vision 5.0a software. 【Result】 The effects of nitrogen application on root development of peanut varieties with different drought resistance were different under different water conditions. Compared with no nitrogen fertilizer, the total root length, total root surface area and the root length and root surface area in 0-20 cm soil layer of Huayu 22 (drought resistant peanut variety) were decreased by application of nitrogen fertilizer under drought stress, while the root biomass, root length and root surface area in the soil layers below 40 cm were increased. The nitrogen fertilizer treatment decreased root biomass, root length and root surface area in 0-20 cm soil layer of Huayu 22 under well-watered conditions, and the root system traits in the soil layer below 40 cm were increased. The root response of Huayu 23 (drought sensitive peanut variety) to water and nitrogen treatment was different from Huayu 22. The total root biomass, total root length, root length and root surface area in the soil layer below 40 cm of Huayu 23 were increased by application of nitrogen fertilizer under drought stress, while the root length and root surface area in the soil layer below 40 cm were decreased under well-watered conditions. The response of root exudates to water and nitrogen in different peanut varieties were consistent. Furthermore, the root exudates of two peanut varieties were decreased under drought stress, and the decreased amplitude of Huayu 23 was larger. Compared with no nitrogen fertilizer, application of nitrogen fertilizer increased root exudates in both peanut varieties under drought stress. The peanut yield of both varieties were increased by application of nitrogen fertilizer under drought stress. The yield of Huayu 22 was increased by application of nitrogen under well-watered condition, however, no significant difference was observed for Huayu 23. And the effects of water and nitrogen interaction on peanut yield were at the significance level in two years. The correlation coefficient between root length and root surface area in the soil layer below 40 cm with yield reached the significance or extremely significant level under drought stress. Under well-watered condition the yield was significantly correlated with the root surface area in 20-40 cm soil layer. The correlation coefficient between root exudates and yield were significant under drought stress and well-watered conditions.【Conclusion】Under drought stress, the root biomass, root length and root surface area of peanut in the soil layer below 40 cm, and root exudates increased by applying nitrogen fertilization. Moreover, root growth was well improved, and that the peanut yield increased simultaneously.

Key words: peanut, root, water and nitrogen interaction, yield, soil layer