农药草甘膦在砂质潮土上的迁移行为及其影响因素

化学物质在土壤中的移动性是人们精确评价其潜在淋溶能力(即对地下水的污染风险)的必要信息。通过一次平衡法和饱和土柱稳定流混合置换实验,来阐明环境pH变化和磷酸盐施用对草甘膦在砂质潮土中的吸附和迁移行为的影响。结果表明,草甘膦在砂质潮土上的吸附量随着pH的增大而降低,在pH4~6的范围内吸附量变化最明显;其穿透曲线(BTCs)均呈现不同程度的不对称性,加入的草甘膦浓度越低这种不对称性越明显;在本实验条件下,施用磷酸盐有抑制草甘膦迁移的趋势,但其抑制趋势并非随磷酸盐施用量的增加而持续增加。如加入草甘膦浓度为500 mg L-1,不加磷酸盐P0时,流出液中草甘膦峰值为459.8mg L-1,而加入磷酸盐P1和P2时,其峰值分别为147.3 mg L-1和373.6 mg L-1。推测其原因可能与磷酸盐施用导致环境pH降低及磷酸盐在加草甘膦前已经占据过多的吸附位点有关。

TRANSPORT BEHAVIOR OF GIYPHOSATE IN SANDY FLUVO-AQUIC SOIL AND ITS INFLUENCING FACTORS

Transport behavior of applied chemicals in soil is essential for evaluating their potential leaching to groundwater.In this study sorption of glyphosate to a sandy Fluvo-aquic soil as affected by pH was determined using batch technique and its transport behavior in the soil as affected by different application rate of phosphate investigated through a miscible displacement experiment under soil-water saturated conditions and constant flux.Results show that the glyphosate sorption decreased with increasing pH,particularly when pH rose from 4 to 6.All measured breakthrough curves(BTCs) exhibited different extent of asymmetry with sharp adsorption and slow desorption fronts,the lower the glyphosate application rate,the more distinct the asymmetry.Ageneral trend of phosphate application inhibiting transport of the chemical was observed,while the trend was not consistent with the application rate of phosphate.For example,when application rate of glyphosate was 500 mg L-1,the peak glyphosate concentration in efflux was 459.8 mg L-1 in Treatment P0,and 147.3 mg L-1and 373.6 mg L-1respectively in Treatment P1 and P2.It is probably because application of phosphate leads to decrease in pH and phosphate occupy adsorption sites in the soil preemptively.