The results of experiments and investigations on the symbiotic nitrogen fixation of soybeaa in lessive region in Heilongjiang Province are summarized as follows:1.In symbiotic system,the soybean modulation showed a high positive correlation with the plant growth.Under different ecological conditions,the divergency in the correlation increased with the increasing rate of nodulation.2.In the early stage of growth,nitrogen fertilizer showed sensitive inhibition effect on the nodulation for 20 soybean varieties,whereas phosphate fertilizer produced favorable effect on the growth,nodulation and the rate of nitrogen fixation of soybean.The application of phosphate fertilizer together with molybdate showed more favorable effect on the symbiotic system.3.The intensive decline of the plant growth,the rate of nodulation and the yield of the soybean were resulted by the continuous cropping of this crop.Applicaof phosphate and molybdate fertilizers,although improved the rate of nodulation and nitrogen fixation,could not correct the unfavourable effect resulted from continuous cropping.4.Under the condition of mechanized cultivation,a significant variation in the rate of natural nodulation of soybean appeared.In some fields,even no any symbiotic fization of nitrogen took place,and in a few fields,the rate of nitrogen fixation reaehed 50 per cent.The highest amount of fined nitrogen was about 0.33 kg/ha,with an average figure of 0.18 kg/ha from 15 scattered locations.