一般认为,由于根瘤菌的固氮作用,大豆出苗后两周只施给它极少量氮肥即可。不过,据知大豆在开花期以后所吸收的氮占总氮量的80％,所以这一时期供给植株的氮素如何,对籽粒产量影响极大。 根瘤菌的固氮能力在大豆即将开花时最高,此后便逐渐下降,因此,在开花至结荚期若能施给适量的氮肥,一般都能获得较高的培肥效果。但开花期追肥不仅受作业方面的影响,而且有时也受气候、土壤的制约,往往易错过施肥适期。 Generally believed that due to nitrogen fixation of rhizobia, two weeks after the emergence of soybean only give it a very small amount of nitrogen fertilizer can be. However, it is known that soybeans absorb about 80% of the total nitrogen after the flowering period, so how nitrogen is supplied to the plant during this period greatly affects the grain yield. Rhizobium nitrogen fixation ability is highest when soybean is about to flowering, then gradually declines, therefore, if flowering to podding stage can give the right amount of nitrogen fertilizer, generally can obtain higher fertilizer effect. However, flowering top dressing is not only affected by the operation, but also sometimes by the climate, soil constraints, often easy to miss fertilization period.