关键词: 苹果, 牧草, 氮素竞争, 氮素促进

Abstract: The effect of planting three kinds of herbage（Trifolium repens Linn.，Lolium perenne L. and Vulpia myuros C.）on the growth and absorption of 15N were studied in field plot using the 15N-labeled tracer method on low nitrogen level（50 kg ? hm-2）and mid nitrogen level（100 kg ? hm-2）in 2-year-old‘Red Fuji’/Malus hupenensis apple saplings. The results showed that，compared with apple monocrops，the biomass，nitrogen acquisition and 15N utilization rate of apple saplings were significantly reduced by planting herbage which was especially true under low nitrogen treatment in spring shoots growth arrest stage；While in autumn shoots growth arrest stage，compared with apple monocrops，the biomass，nitrogen acquisition，15N utilization rate and root activity of apple saplings were significantly increased by planting herbage. In autumn shoots growth arrest stage，the 15N abundance and total N content in 0–20 cm layerwere Trifolium repens Linn. planting > Vulpia myuros C. planting > Lolium perenne L. planting > apple monocrops，but in 20–40 cm and 40–60 cm layer the 15N abundance and total N content were apple monocrops > Lolium perenne L. planting > Vulpia myuros C. planting > Trifolium repens Linn. planting. It indicated that leaching loss of nitrogen fertilizer was reduced by planting Trifolium repens Linn.，Lolium perenne L. and Vulpia myuros C. Gmelin，which benefiting soil fertility remaining but also increasing the nitrogen efficiency，promoting the growth of apple saplings.

Key words: apple, herbage, nitrogen competition, nitrogen facilitation