三峡库首地区土壤养分状况与年际变化

三峡库区长期以来人地矛盾突出，蓄水和移民搬迁使土地资源进一步减少，过度开发引起的土壤肥力下降和生态退化问题日趋严重。通过布点调查和土壤取样，对秭归县水田坝乡区域不同海拔高度和农业土地利用管理方式土壤养分状况及其变化趋势进行分析。结果表明: 研究区域内山地农业已普遍采用梯田进行保护性耕作，海拔600~700 m区域主要开辟为脐橙园，700~900 m区域山地主要种植常规作物；研究区域土壤有明显粗骨化和沙质化特性，其肥力特征是蓄水力偏弱，持水保肥性较差，但通气和透水性好，易耕作；研究区域土壤有机质含量偏低，中高海拔区域土壤有机质、全氮含量相对较高，而低海拔区域土壤全磷、全钾含量较高；坡改梯有利于改善土壤肥力状况，提高土壤氮磷养分含量；根据2005~2010年研究结果，研究区域土壤肥力退化趋势仍未得到控制，同时因水土流失和化肥大量使用，该区域大多数土壤有机质含量、全氮、全磷和全钾含量呈降低趋势，而土壤速效养分含量有增高趋势

SOIL NUTRIENT STATUS AND INTERANNUAL VARIATION IN THE HEAD PART OF THE THREE GORGES RESERVOIR

There is serious contradiction between human and land in Three Gorges Reservoir area for a long time.Water storage and resettlement make land resources further reduce.At the same time,the decrease of soil fertility and ecological degradation caused by excessive development has become more and more serious.Soil fertility and variation tendency of different land use and different altitudes in Shuitianba Village of Zigui County in Three Gorges Reservoir area were analyzed,with soil sampling and investigation.The results show that terraced fields and protective cultivation were commonly used in the study area.The area of altitude 600~700 m was mainly opened for oranges orchard,the area altitude 700~900 m was mainly grow conventional crops.The soils in the study area were featured by thick ossification and desertification,and its fertility characteristics are weak water-retaining property,poor water-stable aggregate,good ventilation and water permeability,and easy farming.Content of soil organic matter(SOM) in the study area was generally low,but content of SOM and total nitrogen(TN) in middle and high elevation area was relative high,and content of soil total phosphorus(TP) and total potassium(TK) in low elevation area was relative high.Slope land changing to terraced fields helped to improving soil fertility and increasing soil nitrogen and phosphorus.According to the continuous monitoring result of 2005~2010 years,soil fertility was generally low in the study area,which became constraints for local agricultural production,and soil fertility degradation trend is still not controlled in mountain area at present.Because of soil and water loss and excessive use of chemical fertilizer,the content of SOM,TN,TP,and TK in most of the soil in the study area decreased,but content of soil available nutrient increased.