云南滇池流域西芹种植区不同施肥条件下的地下水环境氮素污染

Nitrogen Contamination of Groundwater in Relation to Fertilization Practice in Celery Tillage,Dianchi River Basin,Yunnan Province

通过野外田间实验,研究了高量施肥处理、低量施肥处理、不施肥处理以及空白对照裸地等不同施肥处理条件下土壤水中各种形态氮的时空分布情况,探讨了地下水环境中氮素在不同施肥处理条件下的迁移转化特征。结果表明,在各种处理条件下,土壤水中硝态氮质量浓度随深度的增大而减小,而亚硝态氮与铵态氮质量浓度在剖面上的变化幅度较大,这种变化主要受土壤水氧化还原电位的影响。硝态氮随时间的变化趋势在4个处理区表现各异:在高量施肥处理区,各层位的土壤水中硝态氮质量浓度总体上呈增大趋势;在低量施肥处理区,硝态氮受作物生长和灌溉的影响呈拍岸浪式向下迁移;在不施肥处理区和空白对照裸地处理区,由于表层土壤中硝态氮背景值较高(0～30cm处土壤硝态氮平均质量分数达到15.59g/kg),灌溉水的下渗也导致硝态氮向下迁移。高量施肥处理区和空白对照裸地处理区土壤水的对比表明,施肥可促进0.6～1.5m深处土壤的反硝化作用,从而增大这些层位土壤水中亚硝态氮和铵态氮的质量浓度。

The paper studies temporal and spatial variations of nitrogen(including nitrate nitrogen, nitrite nitrogen and ammonium nitrogen) concentrations in soil waters and groundwaters in relation to various treatments, namely, high fertilizer treatment, low fertilizer treatment, no fertilizer treatment and no plant (CK) treatment, in celery tillage, and discusses the characteristics of nitrogen transformation and transport in soil water and groundwater under those treatments in celery tillage. Nitrate nitrogen concentration in soil water decreases with an increase of sampling depth below land surface under all treatments. Nitrite nitrogen and ammonium nitrogen concentrations in soil water vary drastically with sampling depth from 0.3 m to 2.8 m, which results from Eh in soil water. The change of nitrate nitrogen concentration with time is different in each treatment. The soil water at all depths contains more and more nitrates in the high fertilizer treatment, which indicates that nitrate continuously moves downward. Affected by celery growth and irrigation, nitrate transports downward in wavy style in the low fertilizer treatment. Due to high background value of NO_3-N concentration in topsoil(the mean of nitrate nitrogen concentration in 0-30 cm topsoil is up to 15.59 g/kg), the infiltration of irrigation water results in nitrate transport from topsoil to aquifer in no fertilizer treatment and CK treatment, contributing to an increase of NO_3-N concentration in water at depth greater than 1.8 m under land surface. Nitrite nitrogen and ammonium nitrogen concentrations in water sampled at the depth of 0.6 m and 1.5 m below land surface from high fertilizer treatment are much higher than those from CK treatment, demonstrating that fertilization promotes denitrification.