The effect of N，P and variability of their use efficiency on winter wheat in the rainfed highland

The obvious effect of nitrogen and phosphorus on winter wheat in rainfed highland has been demonstrated by the long-term experiment,but this effect could change with varieties and years.Nitrogen use efficiency or phosphorus use efficiency not only had the clear change in different years,but decreased with increase of the amount of N or P applied in 1984～1995,nitrogen use efficiency was in 6.4%～58.6%,the coefficient of variability was 48.7%,phosphorus use efficiency was in 3.7%～19.8%,the coefficient of variability was 39.5% on Changwu-131 wheat.During 1996～1998，nitrogen use efficiency was reduced from 42.9% to 25.4%,phosphorus use efficiency was reduced from 10.8% to 3.2% on Changwu-134 wheat while the amount of N or P₂O₅ was used from 45kg/hm² to 180kg/hm².Since the profit and use efficiency of fertilizers could not keep same step,evaluating that the fertilizer's benefit by fertilizer use efficiency had the big limitations in the rainfed region.By analyzing effect of N and P mutual promoting,it was showed that mixture applying of N and P was an effective way to improve nitrogen use efficiency and phosphorus use efficiency each other.