为探究大豆品种在遗传改良过程中根系伤流液含氮化合物的变化规律，以吉林省1923-2009年间育成的29个大豆品种为材料，在不同生育时期测定根系伤流液中的硝态氮、铵态氮以及游离氨基酸（FAA）的浓度、总量。结果表明：大豆根系伤流液中含有大量的FAA；大豆品种的遗传改良增加了根系伤流液中硝态氮、FAA的浓度和总量，但铵态氮的浓度有所降低，其总量随着育成年代的变化不显著；同一大豆品种根系伤流液中的氮浓度随着生育时期的推进而降低，氮总量由于受到其浓度和伤流强度的共同影响，表现为R4期最高，R2期次之，R6期最低。由此说明大豆品种的遗传改良提高了根系伤流液中含氮化合物的水平，R2期氮代谢最为旺盛，是大豆需氮的关键时期，应注意合理追施氮肥。 

In order to understand the changes of nitrogen compounds in root bleeding sap during the genetic improvement of soybean varieties, 29 soybean varieties bred in Jilin Province during 1923- 2009 were used to measure the concentration and total amount of nitrate, amide and free amino acids (FAA) in root bleeding sap at different growth stages. The result showed that there were great amount of FAA in soybean root bleeding sap; the concentration, total amount of nitrate and FAA increased with genetic improvement of soybeans cultivars, while the amide concentration decreased and the change of the total amount was not significant with year of release. Nitrogen concentration in root bleeding sap of the same soybean variety decreased with the proceeding of growth stage. The maximum total nitrogen amount was at R4 stage, the second was at R2 stage and the minimum was at R6 stage. It was concluded that genetic improvement of soybean varieties improved the level of nitrogen compounds in root bleeding sap, and nitrogen metabolism was the most vigorous at R2 stage. R2 stage was the critical period requiring extra nitrogen and the nitrogen fertilizer should be applied at this time.