放牧强度对新麦草人工草地氮素在牧草与土壤中的分配和动态的影响

Nitrogen Distribution at Grass-Soil System and Growing Dynamic on Russian Wildryegrass Pasture as Influenced by Grazing

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。

The N distribution at grass-soil system and growing dynamic under light grazing(LG 0. 134 hm2/sheep), medium grazing (MG0. 08 hm:/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 N concentration 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 -N over the growing season (June-September). Medium grazing is good to grass N utilized 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 N at grazed site was higher than that at ungrazed site,and grazing result in more N allocation in roots,the allocation of nitrogen in aboveground was lower than that at ungrazed site.