等高草篱对坡耕地土壤苯磺隆残留迁移的影响

在北京市昌平区冬小麦田采用模拟降雨的方法，对不同坡位（坡中和坡底）的土壤进行分层（0~5、5~10、10~15 cm）取样测定，研究了草木樨和狼尾草两种等高草篱在不同雨强（15、20 mm·h-1）和坡度（15%和20%）条件下对土壤苯磺隆残留迁移及分布特征的影响。结果表明，前期干旱条件下，降雨后土壤苯磺隆残留纵向迁移特征明显，无明显的水平移动，亦未产生残留径流输出。草篱能够促进土壤中苯磺隆残留向下迁移，导致草篱带内和无草篱区域土壤中的残留纵向分布特征有较大差异：草篱带内3个土层残留水平相近，而对应坡位无草篱区域残留主要滞留于土壤表层，并随土层加深而显著降低。雨强、草篱、坡度均对土壤苯磺隆残留量有显著影响，草篱的贡献超过雨强和坡度，成为影响坡耕地农药残留纵向迁移行为的首要因素。

Effects of contour grass hedges on migration of tribenuron-methyl residue in sloping cropland soil

Here we evaluated the effects of two grass hedges, Melilotus officinalis and Pennisetum alopecuroides, on migration and distribu-tion of tribenuron-methyl residue in sloping cropland soil. Experiments were carried out in winter wheat(Triticum aestivum)field on 15%and 20% gradient slopes in the Changping District of Beijing, China, under simulated rainfall(rainfall intensity at 15 and 20 mm·h-1). Soil samples were collected from the middle and bottom positions of the slope at three depths(0~5, 5~10 and 10~15 cm). Results indicated that the movement of tribenuron-methyl in soil was dominated by vertical migration when rainfall events occurred after a long dry period. The horizontal migration was not obvious, with no residues detected in the surface runoff. Grass hedges accelerated the vertical migration of tribenuron-methyl residues. The residual levels of tribenuron-methyl did not differ among 3 soil depths inside the hedges, whereas tribe-nuron-methyl residues were markedly higher in topsoil than in subsurface soil, and decreased significantly with increasing soil depth in slope areas without hedges. Grass hedge, rainfall intensity and slope gradient significantly influenced the transport of tribenuron-methyl residues in soil. The optimal scaling regression showed that grass hedge was the dominant factor, followed by rainfall intensity and slope gra-dient, in controlling pesticide migration on sloping croplands.