青海湖农场退耕还林草后的土壤碳氮变化

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（N_inorg）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N_inorg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0.11 t C·a^-1·hm^-2,N的损失率为0.015 t N·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。

How Did Soil Organic Carbon and Total Nitrogen Change After “Grain for Green” in the Qinghai-Lake Farm

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 (N_inorg) concentration, pH, bulk density were determined. The results showed that three land-use types had alkaline soils. The bulk densities and N_inorg 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 & 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 & TN concentrations only in 0~5 cm layer had a smaller increase after "grain for green" for about 10 years comparing with cropland, indicating that the recovery of soil fertility would take a longer 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 depended on both soil nutrients and bulk densities. Therefore, soil bulk density is an important factor in the process of soil quality improvement.