中文摘要：

为量化不同生育时期氮肥施用量与大豆共生固氮能力和产量的关系，探索既不抑制大豆共生固氮能力，又能提高大豆产量的氮肥施用量，以黑农35为材料，采用盆栽试验，通过在V2、R1、R3和R5期施用不同量的氮肥，测定不同生育时期根瘤数量、干重和固氮酶活性及成熟期的产量，研究氮肥施用时期和施用量对大豆根瘤共生固氮能力和产量的影响。不同生育时期处理的大豆根瘤干重、数量和固氮酶活性大小在R6期均表现为V2〉R5〉R3〉R1，且不同生育时期氮肥施用量与大豆根瘤干重、数量和固氮酶活性间均具有显著的线性负相关关系。不同生育时期处理的干物质积累量和产量在R6期均表现为R1〉R3〉V2〉R5。V2、R1和R3期不同氮肥施用量处理，均显著地促进大豆生物量和产量的增加，而R5期不同氮肥施用量处理与CK处理间的生物量和产量差异不显著。不同生育时期处理均以施氮量225kg·hm^-2的生物量和产量最高。R1期是决定大豆固氮能力和产量高低的关键生育时期，不同生育时期对氮肥施用量的要求存在差异。

英文摘要：

In order to quantify the relationship between the nitrogen application rate and the ability of nitrogen fixation, and find the critical threshold of nitrogen application rate at different growth stage which could improve soybean yield and had no adverse effect on N2 fixation ability. Pot experiment were conducted taking Heinong 35 as test material, total fertilizer N were applied at vegetative stage（ V2）, early bloom（ R1 ）, early pod（ R3 ）and grain fill（ R5 ）, respectively,with five application rates （0,75 150,225,300 and 375 kg·ha^-1 ） ,and the nodule number,biomass,nitrogenase activity and yield were determined. Nitrogen applied at different growth stage remarkably decreased nodule number, biomass and nitrogenase activity at R6 with an order of V2 〉 R5 〉 R3 〉 R1. There were significantly negative linear correlations between nodule number, biomass and nitrogenase activity and the nitrogen application rate. Moreover,the trends of dry matter accumulation and yield were expressed as an order of R1 〉 R3 〉 V2 〉 R5 ,among which nitrogen applied at V2 ,Rland R3 had significant promoting effect. At each stage,the nitrogen application rate of 225 kg· ha^-1 had the highest dry matter accumulation and yield. There was different threshold of nitrogen application rate at different growth stage,and R1 was the crucial stage to determine the ability of nitrogen fixation and yield.