中文摘要：

土壤肥力能反映植物的生长潜力和表现,但又受到植物的影响。在多年生草地系统中,利用年限（牧草年龄）对土壤肥力的影响还没有准确的阐述。采用灰色关联度分析法,对6个年龄紫花苜蓿（Medicago sativa）草地土壤碳、氮、磷、钾等指标进行综合分析,以关联度进行排序对不同年龄草地土壤肥力进行评价。结果表明,在不同土层,紫花苜蓿草地土壤有机碳、全氮、铵态氮、硝态氮、全磷、速效磷和全钾含量随年龄而变化的趋势不一致。运用灰色关联度分析后发现,0-10和10-20 cm土壤肥力最好的年龄均为5龄草地,而20-30 cm土壤肥力最好的年龄为8龄,5龄草地次之。因此,从土壤肥力角度可确定黄土高原地区5龄紫花苜蓿草地利用最佳。

英文摘要：

Soil fertility reflects the performance and growth potential of plant which is easily affected by the plant.In the perennial grassland-ecosystem,the effect of forage age on the soil fertility has not been clearly elucidated yet. In the present study,the soil fertility in lucerne stands with six different ages were comprehensively analysed using grey correlative degree analysis to evaluate the effect of stand age on soil fertility. In different soil layers,the contents of organic carbon,total nitrogen,ammonium,nitrate,total phosphorus,available phosphorus and total potassium were different in different lucerne stands cultivated in different years,and they differently varied with stand age. Using grey correlative degree analysis,the best soil fertility was observed in 5-year old stands in 0- 10 and 10- 20 cm soils,the best soil fertility was observed in 8-year old stands and the better soil fertility was observed in 5-year old stands in 20- 30 cm soils. Conclusively,in the Loess Plateau,the optimal utilisation age of lucerne was5-year old considering soil fertility.