中文摘要：

对青海湖农场退耕还林草地以及耕地和天然草地的土壤有机碳（SOC）、全氮（TN）含量及储量、无机氮（Ninorg）含量、土壤pH等基础理化指标进行了测定分析.结果表明：退耕（还林草）地与耕地和天然草地土壤均偏碱性;退耕地及天然草地土壤容重及Ninorg含量均低于耕地;退耕地和天然草地0～5 cm土层C/N显著高于耕地;退耕地和耕地0～5,5～10,10～20 cm土层的SOC和TN含量低于天然草地;退耕还林草9年后各土层SOC和TN含量与耕地相比差异不显著,说明青海湖区持续耕作60多年后,要恢复土壤肥力仍需较长时间;对于0～30 cm土层的SOC及TN储量,退耕地和天然草地与耕地无显著差异,而退耕地与天然草地之间差异显著（P＜0.05）;耕地、退耕地以及天然草地0～20 cm土壤SOC含量分别占0～30 cm土层SOC储量的68.7％,72.9％和78.6％;0～20 cm土层TN含量分别占0～30 cm土层TN储量的68.7％,72.7％和78.2％;与天然草地相比,按耕地开垦60年计算,0～30 cm耕层内,C的损失率为0.11tC＆·a-1＆·hm-2,N的损失率为0.015tN＆·a-1^·hm-2;土壤C和N含量与容重共同决定C和N储量的大小,因此土壤容重是影响土壤质量的重要因素之一.

英文摘要：

Soil physio-chemical properties of three land-use types （abandoned farmland-grain for green, cropland and natural grassland） in Qinghai-Lake farm, such as soil organic carbon （SOC）, total nitrogen （TN） and inorganic nitrogen （ Ninorg ） concentration, pH, bulk density were determined. The results showed that three land-use types had alkaline soils. The bulk densities and N~,o,g contents of abandoned farmland and grassland were lower than those of cropland. The soil C/N ratios of abandoned farmland and grassland were higher than that of cropland in 0~ 5 cm. The SOC ga TN concentrations of abandoned farmland and cropland in 0~5 cm, 5~10 cm, and 10~20 cm layers were lower than those of natural grassland. SOC g~ TN concentrations only in 0~5 cm layer had a smaller increase after ＂grain 5or green＂ for about 10 years comparing with cropland, indicating that the recovery of soil fertility would take a 10n- ger time after continuous cultivation for more than 60 years. Both SOC and TN storages in 0~30 cm soil layer were no significant difference between cropland and abandoned farmland or grassland, while there was significant difference between abandoned farmland and grassland. The storages of TOC and TN de- pended on both soil nutrients and bulk densities. Therefore, soil bulk density is an important factor in the process of soil quality improvement.