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在禾谷类连作体系中，非肥料性投入的氮源每年每公顷在３０ｋｇ以上．我们研究了由作物根系相联系的生物固氮（ＢＮＦ）或者植物残体作用造成非肥料性氮投入的可能性。供试小麦生长在温室条件下的盆（盆高３４ｃｍ，直径１０ｃｍ）中，盆内土壤取自一个试验小区，该小区自１９１１年以来，一直种植春小麦且一直没有施用化肥。在营养主长期、生殖生长期及生长后期，供试小麦的根和土壤与大气隔离，并置于充足的￣１５Ｎ＿２气体中长达３—４周。这种方法最少测得值是：植物材料中，单株固氮１μｇ；土壤材料中，单株固氮为４０μｇ。在前两个标记时期，没有出现对￣（１５）Ｎ＿２的固定作用，而在最后一个时期，还田的麦秆明显的被￣（１５）Ｎ＿２所肥化，特别是在土壤湿度高的试验盆中尤为明显，这个盆中总的生物固氮量为每株１３μｇ，每公顷大约３０ｇ。
In cereal cropping systems, the non-fertilizer input nitrogen source is above 30 kg per hectare per year. We investigated the possibility of non-fertilizer N inputs resulting from the action of biological nitrogen fixation (BNF) or plant debris linked to crop roots. TESTED WHEAT GROWTH In basins (34 cm pot height, 10 cm diameter) under greenhouse conditions, the potted soil was taken from a pilot plot that has been growing spring wheat since 1911 and has not been fertilized. During vegetative and reproductive growth and late growth, the roots and soil of the tested wheat were isolated from the atmosphere and placed in sufficient air for ~ 3-4 weeks. The minimum measured value of this method is: plant material, nitrogen fixation 1μg; soil material, the nitrogen fixation of a single plant 40μg. In the first two marked periods, no fixation effect was found on N_2 (15), whereas in the last period the straw returning to the field was apparently fertilized by (15) N_2, especially in high soil moisture This is particularly evident in pots, where the total biological nitrogen fixation is 13 μg per plant and about 30 g per hectare.