Abstract: The N distribution at grass-soil system and growing dynamic under light grazing(LG 0.134 hm²/sheep), medium grazing (MG0.08 hm²/sheep), high grazing (HG 0.067 hm²/sheep), and no grazing (CK)was carried out on a pasture established using Russian Wildryegrass (PSathyrstachys juncea(Fishch)NeVki)during growing season (from June to September)in 1997. The total Nconcentration of the pasture was 663.5～938.4g/m²,the most of which (99% )was present in the soil,less then 1% was present in the plant. The soil layer of O-2ocm contained 60～70% of the total N.There were no significant changes in soil -Nover the growing season (June-September). Medium grazing is good to grass Nutilized rate. The nitrogen reserve in soil showed a "T"-pattern in distribution and decreased exponentially with soil depth and had a tendency to accumulate at soil surface with increasing of grazing intensity,while there was no such tendency at ungrazed site. SOil N percentage at high grazing site was highest,and the others is ranked as CK>LG>MG,the plant Nat grazed site was higher than that at ungrazed site,and grazing result in more Nallocation in roots,the allocation of nitrogen in aboveground was lower than that at ungrazed site.

Key words: Grazing intensity, Soil nitrogen allocation, Nitrogen cyclingl Nitrogen percentage

摘要： 本文研究放牧强度对新麦草草地氮素在牧草和土壤中的分配与季节动态。结果表明,草地氮素贮量在0～30cm土层为每平方米663.5～938.4g,其中70％集中于0～20cm。土壤氮素随着时间的变化没有显著差异。中度放牧可提高牧草对氮素的利用率。随着土层的加深,氮素呈“T”型分布,其中以中度放牧最为明显。随着放牧强度的增加,表层氮素的积累增多,以对照区土壤氮素的含量最高,重牧区次之,中牧区最低(P<0.05)。对照区植物活体中氮素的比例高于放牧区。放牧区根系氮素的比例高于对照区。

关键词: 放牧强度, 氮素贮量, 氮素分配比例, 氮素百分含量, 新麦草人工草地