Abstract: It was showed in the plot experiment that ¹⁵N-urea (75kg/ha) applied stimulated obviously growth and herb yield of orchard grass, and recruitment of N% for orchard grass was higher than perennial ryegrass in Huoshaoping exerimental pasture of the midmountain area, the subtropic zone.Dinitrogen fixation for red clorer cv.Badong reduced, significantly, but did not for white clover cv.Huyia.%Ndfa for them were 81.95-93.24% and 56.64-69.84%, respectively.In the pasture, %Ndfa for red clover was 91.82±7.65% and 54.74±12.34% for white clover.In 50 days, 36.02% of 15N-urea applied was uptaken by plants, 46.79% was residual in soil and 17.18% losed in mixed culture of legumes and grasses, but 28.44%, 34.29% and 37.02% in mixed culture of only grasses.It was showed that the planting pattern of legumes mixed with grasses was better than that of grasses in mixture.In the case of application of 75kg urea per hectare, grasses mainly uptook soil N, the %Ndfs was up to 62.41-72.87%.Legumes mainly uptook air N for their growth and reproduction by symbiotical dinitrogen fixation.

Key words: Legumes and grasses, Symbiotical dinitrogen fixation, ¹⁵N-urea

摘要： 试验结果表明,亚热带中山草地施入75kg/ha¹⁵N-尿素能明显提高鸭茅产草量,其N%的增加显著高于多年生黑麦草;豆科牧草的N%不受施氮的影响。但是,巴东红三叶的固氮活性因尿素的施入而显著降低,胡依阿白三叶则无明显变化。前者固定空气氮量占植株地上部全氮量的81.95～93.24%,后者为56.64～69.84%。草场中生长10年以上的红三叶固氮百分率为91.82±7.65%,白三叶为54.74±12.34%。¹⁵N-尿素施入50天内豆禾牧草混播植株吸收利用36.02%,土壤残留46.79%,仅有17.18%的尿素损失;而混播禾本科牧草分别为28.44%、34.29%和37.20%。表明豆禾牧草混播显著优于禾本科牧草混播。在施入少量化合态氮素的情况下,禾本科牧草主要吸收土壤氮素,其吸收量占植株全氮的62.41～72.87%,豆科牧草则主要依靠共生固氮满足其生长和繁殖所需。

关键词: 牧草, 生物固氮, ¹⁵N-尿素