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采集长期定位试验（14年）土壤（棕壤）进行盆栽试验，并应用同位素15N示踪技术研究了土壤中微生物对肥料氮的固持及其动态。结果表明，施肥后5天土壤微生物对施入化肥氮的固持达到最高，除单施氮肥处理的固持量占施入化肥氮量的5.4％外，其余各处理均在13.3％-15.4％间。施肥后土壤微生物生物量氮的增加主要来自化肥氮，后者占微生物体总氮量的64.1％—87.3％。在作物生长期间微生物固持的化肥氮逐渐释放出来，在小麦分蘖期微生物固持的化肥氮明显减少，仅占施肥量的1.72％—3.29％。在分蘖期以后微生物固持态15N的变化趋于稳定。由微生物体释放的15N量占作物吸收15N的比例除单施氮肥处理较高外，占83.7％，其它施肥处理在34.3％—54.3％间。微生物体释放的15N量与小麦吸收15N量之间存在明显的正相关（r＝0.860，n＝6）。
Soil samples (brown soil) from long-term experiment (14 years) were collected for pot experiment, and isotope 15N tracer technique was used to study the nitrogen fixation of soil microorganisms and their dynamics. The results showed that the soil microorganisms had the highest nitrogen fixation on the 5th day after fertilization, except for the single application of nitrogen fertilizer, which accounted for 5.4% of the total amount of nitrogen fertilizer, while the other treatments were between 13.3% and 15.4%. After fertilization, the increase of soil microbial biomass nitrogen mainly came from fertilizer nitrogen, which accounted for 64.1% -87.3% of the total nitrogen of microbial population. Fertilizer nitrogen retained by the microorganisms gradually released during crop growth. Fertilizer nitrogen retained by the microorganisms at the tillering stage of wheat decreased significantly, accounting for only 1.72% -3.29% of the amount of fertilizer applied. After the tillering stage, the change of 15N in microbe kept stable. The proportion of 15N released by microorganisms accounted for 83.7% of the total nitrogen absorbed by plants and 34.3% -54.3% of other fertilization treatments except for the single application of nitrogen fertilizer. There was a clear positive correlation between the amount of 15N released by microorganisms and the amount of 15N absorbed by wheat (r = 0.860, n = 6).