Effect of Nitrogen Levels on Physiological Characteristics and Yield of Different Soybean Varieties

In order to understand the response of some physiological characteristics and yield to nitrogen levels in soybean varieties with different nitrogen photosynthetic efficiency,the study on the root activity,nitrate reductase activity,nitrogen content of leaf,chlorophyll content,net photosynthetic rate,dry weight of single plant and yield of two high-level and two low-level nitrogen photosynthetic efficiency varieties under five nitrogen levels from R2 to R6 stage was conducted.The results showed that the change in physiological characteristics and yield of four soybean varieties showed a single peak curve which were increased at the beginning and then decreased with the nitrogen levels.The comparisons of different nitrogen photosynthetic efficiency varieties released in similar years showed that the root activity,nitrate reductase activity,net photosynthetic rate,dry weight of soybean varieties with high level nitrogen photosynthetic efficiency was higher than low level varieties at low nitrogen(40-80 kg·ha-1)treatment,but it was lower than the low level varieties at high nitrogen(120-160 kg·ha-1)treatment,the differences reached extremely significant level(P0.01)at R6 stage,and they were significant(P0.05)or non-significant at R2 stage and R4 stage.Total nitrogen content and chlorophyll content in leaves of varieties with high level of nitrogen photosynthetic efficiency were significantly lower than the low level in five nitrogen levels.So the medium and low amount of nitrogen fertilizer should be applied for varieties with high nitrogen use efficiency,similarly,increasing the corresponding amount of fertilizer to apply for varieties with low nitrogen use efficiency was feasible.