黄土丘陵沟壑区退耕地人工林的土壤环境效应

Soil EnvironmentalEffects of Artificial Woods in Abandoned Croplands in the Loess Hilly-gullied Region

根据延安、安塞和吴旗退耕20年以上人工林地、自然恢复草地和坡耕地的调查与分析资料,分析了人工林相对于坡耕地、自然恢复草地、次生林的土壤环境效应,包括土壤有机质的积累、土壤氮磷钾素的变化、土壤水分效应和水稳性团聚体的特征.结果表明:人工林可明显地提高土壤有机质、全氮、有效氮和速效钾的含量,特别是0～20cm土层,但这些土壤肥力指标仍处于低或中等水平;同时人工林地土壤的水稳性团聚体含量较高,增强了土壤的抗侵蚀能力;但人工林对土壤水分的消耗却远远大于坡耕地和自然恢复的草地,在安塞和吴旗表现得更为明显.综合分析结果和黄土丘陵沟壑区特殊的自然环境特征,认为在黄土高原丘陵沟壑区,退耕地的植被恢复宜采取先封禁牧,然后补种部分适宜的牧草、灌木和乔木,逐步实现良好的乔灌草植被结构特征和其生态环境功能.

Based on the data obtained in artificial wood lands and naturalrestoration lands over 20 years in Yanan,Ansai and Wuqi,the soil environmental effects of the woods including soil organic matter accumulation,variations of N,P and K,soil water content and soil water stable aggregatecontent were evaluated and compared with that of croplands,naturalrestoration lands and secondaryforest lands.The results showed thatthe woods could increase soil organic,total N,availableN and easilysoluble K evidently,especially in the 0～20 cm soil layers;but these fertilityindexes in artificial lands were still in low or middle level.Moreover the soil water stable aggregatecontent in the wood lands was higher,and the erosion resistant capacitywas improved.However,the trees consumedmuch more soil water than in arable lands and natural restorationlands,and this was more obvious in Ansai and Wuqi.Accordingto the results and special characteristicsof naturalenvironment in the loess hilly-gullied region,it was considered that vegetation restoration in abandoned croplands should be spontaneousrestoration withoutgrazing and human disturbances in the early stage.