典型水稻土中硝态氮垂直穿透状况及模拟

Study on the situation of the nitrate-N's vertical breaking-through of the soil in the typical rice fields and simulation by Hydrus-1D model

硝态氮(NO3--N)不但可以污染地下水,也会造成河流和湖泊的富营养化。用穿透曲线(BTCs)描述室内土柱模拟的NO3--N在太湖地区3种典型水稻土(白土、黄泥土和乌栅土)中的垂直穿透状况并用Hydrus-1D模型对实验结果进行了拟合。结果表明,3种水稻土中NO3--N穿透土壤各土层所用的平均时间按从长到短的顺序为:黄泥土、乌栅土、白土,而峰值大小则正好相反,从大到小依次为:白土、乌栅土、黄泥土。因此,在白土样区过量施用氮肥最容易对水体造成污染。3种水稻土中NO3--N的穿透曲线都呈不对称分布,曲线尾部均存在一定的拖尾现象。通过对NO3--N穿透土壤的影响因素的分析可知,土壤容重和粘粒含量是影响NO3--N穿透的主要因素,土壤容重越大或粘粒含量越高,穿透所需的总时间就越长,峰值就越低且拖尾现象越严重;有机质含量对其也有一定的影响。用Hydrus-1D模型对实验结果进行模拟,所得的穿透曲线的模拟值与实测值均呈极显著的正相关关系,相关系数都在0.9以上。同时,在模拟过程中还得到了土壤饱和导水率和NO3--N的垂直扩散率等难以实测的参数,说明利用Hydrus-1D模型不但可以准确地预测NO3--N在研究区土壤中的运移状况,也可以推算出该地区水分和养分运移的参数。

The paper is concerned about the authors＇ study on the situation of the nitrate-N＇s vertical breaklng-through of the soil in the typical rice fields and a corresponding mathematical simulated model. To analyze the vertical breaking-through situation of NO3^--N, the paper has done a few particular measurements with the breaking-through curves （BTCs） of NO3^--N and collected a needed amount of experimental soils from the Taihu Lake area （including Bai soil （White soil） from Yixing region, Huangni （yellow-mud） soil and Wushan （blackgrate） soil from Changshu County, Jiangsu）, The results of our investigation and analysis can be stated briefly as follows： （1） The penetrative velocity of NO3^--N proves to be lower while its break-through process of NO3^--N can be permeated from the surface layer to the bottom in the same soil profile. According to the BTCs, the length of permeating time of NO3^--N ranges from high to low as Huangni soil 〉 Wushan soil 〉 Bai soil, whereas the actual values of the BTCs range from high to low as from Bai soil 〉 Wushan soil 〉 Huangni soil; （2） It can be found from the analysis of the NO3^--N break-through curves of the three kinds of rice soils that all the three curves are unsymmetrical with a certain trail. The soil bulk density and the clay content are the chief influential factors in NO3^--N infiltration. The trail of the breaking-through curves can be delayed quite noticeably. The higher the soil bulk density and the higher the soil organic matter content, the longer the time needed for the breakthrough and the more serious the trail-delay phenomena, （3） In addition, the organic matter content is also an influential factor; （4） When the Hydrus-1D model is used to simulate the penetrating process, it is found that the simulation value and the actual investigated value are positively correlated with the correlative coefficient of BTCs being over 0.9 on the whole; （5） From the above model, we can also gain some parameters of soil solution transfer. Thus, all the above results prove that the Hydrus-1D model is a useful tool to simulate the infiltration of NO3^--N for the soils of the Taihu Lake region.