黄土坡地几种退耕植被土壤硝态氮分布特征与迁移研究

以荒坡地为对照,研究了黄土高原退耕还林中广泛种植刺槐、柠条、苜蓿、杨树、侧柏的土壤中NO3--N的分布特征。结果表明：0～160cm土层中上述不同植被土壤NO3--N的平均含量由高到低依次为柠条〉刺槐〉苜蓿〉侧柏、杨树〉荒坡地（P〈0.05）;人工林地土壤NO3--N含量大于荒坡地,豆科植被大于其他植被;从整个土壤剖面看,这几种植被在0～20cm表层土壤中NO3--N含量均高于其底下各土层,以苜蓿最高,达到6.12mg.kg-1,柠条次之,为5.82mg.kg-1;随着土层深度的增加,在20～60cm柠条、苜蓿和刺槐土壤中NO3--N含量随深度增加逐渐下降,并于60cm以后趋于稳定,杨树、侧柏与荒坡地NO3--N含量随土层的加深变化不大;各植被在140cm以下土层中均存在NO3--N富集现象;不同坡位的NO3--N均呈现坡顶〉坡中〉坡底的趋势,阴坡土壤的NO3--N含量显著高于阳坡（P〈0.05）。

Soil Nitrate Nitrogen Distribution and Transportation Under Several Vegetations on the Reconstructed Sloping Land in the Loess Plateau

Leaching of nitrate nitrogen is an important contributor to the non-point pollution and eutrophication,and it is harmful to human by food chain.Most of the researchers give more concerns on nitrate nitrogen leaching by fertilization,few research have reported on the distribution and transportation of nitrate nitrogen in sloping land.In this study,soil nitrate nitrogen distribution was conducted under 5 vegetations on reconstructed sloping land in the Loess Plateau.The result indicated that vegetation reconstruction improved soil nitrate nitrogen,its content shown as Caragana KorshinskiiRobinia pseudoacaciaMedicago sativaPlatycladus and Populus tremulawasteland（P0.05） in whole profile.Soil nitrogen content of legume vegetations was higher than non-legume.The top layer（0~20 cm） had the highest nitrate nitrogen,especially for Medicago sativa and Caragana Korshinskii,the content were 6.12 mg·kg-1 and 5.82 mg·kg-1 respectively.With the increase of depth,soil nitrate content of Caragana Korshinskii,Medicago sativa and Robinia pseudoacacia decreased gradually,and tended to be stable under 60 cm,while little changes was found for Populus tremula,Platycladus orientalis and slope wasteland in the same layer.The distinctive founding was nitrate nitrogen enriched in all selected vegetations under 140 cm.Additionally,the nitrate nitrogen content was highest in the top slope,followed by middle slope and down slope,and it was significantly higher in the sunny slope than shade slope.Therefore,legume vegetations had the higher contribution on nitrate nitrogen accumulation,transportation of nitrate nitrogen was affected by position and direction of the slope,and vegetation reconstruction could reduce transportation speed effectively in the Loess Plateau.