宁夏灌区不同类型农田土壤氮素累积与迁移特征

在宁夏灌区选择设施菜田(n=4)和水旱轮作大田(n=4),通过田间多点取样观测和室内分析的方法,研究了2种类型农田土壤氮素累积与分布特点,以及其迁移对浅层地下水的影响。结果表明,设施菜田0~150 cm土壤剖面溶解性总氮(TSN)、硝态氮(NO3--N)和溶解性有机氮(SON)含量都显著高于大田,前者分别是后者的1.5~5.6、1.5~3.4倍和1.6~9.8倍。设施菜田土壤氮素主要累积在0~5 cm和5~20 cm土层,而大田主要在40~100 cm土体。设施菜田和大田土壤溶解性总氮占全氮比例分别在5.4%~11.5%和2.2%~4.9%之间,前者的淋失风险较高。设施菜田各形态氮素累积量表现为SONNO3--NNH4+-N,大田为NO3--NSONNH4+-N。设施菜田浅层地下水中TSN、NO3--N和SON含量也都显著高于大田,前者平均含量分别是后者的9.5、13.8倍和7.0倍。因此,硝态氮和溶解性有机氮都是2种类型农田氮素累积的主要形态,也是浅层地下水污染的重要来源。

The Characteristics of Soil N Accumulation and Movement in Different Farmlands in the Yellow River Irrigation Region of Ningxia,China

The greenhouse fields(n=4)and open fields with rotation of paddy-upland crops(n=4)were chosen in the Yellow River Irrigation Region of Ningxia. A method of multiple-points field sampling investigation and laboratory analysis was conducted to study the charac-teristics of soil N accumulation and distribution in different soil profiles and its movement effect on N content in the shallow groundwater from two different farmlands. The results indicated that total soluble N(TSN), NO3--N and soluble organic N(SON)contents in 0~150 cm soil in greenhouse fields were significantly higher than that in open fields, and the average contents in the former fields were 1.5~5.6, 1.5~3.4, 1.6~9.8 times as that in the latter fields, respectively. Different forms of N were mainly accumulated in 0~5 cm and 5~20 cm soil depth in green-house fields, and which were accumulated in 40~100 cm soil depth in open fields. Soil TSN accounted for TN by 5.4%~11.5% and 2.2%~4.9% in the greenhouse and open fields, respectively, and the former had a higher risk of soil N leaching losses. Different forms of dissolved N accumulation amount were SON>NO3--N>NH4+-N in 0~150 cm soil in greenhouse fields, and with the order of NO3--N>SON>NH4+-N in open fields. The TSN, NO3--N and SON contents in the shallow groundwater in greenhouse fields were also significantly higher than that in open fields, the former were 9.5, 13.8, 7.0 times as that in the latter, respectively. Therefore, both NO3--N and SON could be important soil N accumulation forms in these two different farmlands, and that may pollute the shallow groundwater in these two different fields.