非点源污染研究中土壤溶解性无机氮的提取方法选择

用2M KCl溶液(5:1)、饱和CaSO4溶液(5:1)、0.01M CaCl₂溶液(20:1,100:1) 和去离子水(20:1,100:1)4种提取液、6种提取方式,采用Auto-analyzerⅢColorimeter (Bran Luebbe),水杨酸-次氯酸盐法和Griess-Ilosvay法测定并对比了北京地区4种天然土样的溶解性氨氮和硝态氮的含量。研究结果表明:溶解性硝态氮的测定结果不受提取液和水土比(小于100:1)的影响,而溶解性氨氮测定结果受影响较大。在非点源污染研究中,对于土壤中可向水体迁移的溶解性无机氮含量的测定,应根据来水水源特征和研究目的选择适宜的浸提剂和水土比。

Comparison of extraction methods on soil-soluble inorganic nitrogen in non-point pollution research

Dissolved inorganic nitrogen of soil is liable to be transferred into surface or subsurface waters with surface or subsurface runoff. So it is important to measure ammo-niac(NH₄⁺) and nitrate(NO₃^-) in soils for estimating non-point pollution nitrogen load in a drainage area. Commonly, saturated CaSO₄ solution and 2M KCl solution are respectively used as soil extractant for NO₃^-and NH₄⁺ Their efficiencies are high and experimental results are stable. But it is uncertain whether the two methods are fit for non-point pollution research because the output characteristic of soil-soluble inorganic nitrogen is not only related with soil content but also is influenced by soil solution environment. Characteristic of natural rainfall and irrigation water is respectively similar to deioned water and 0. 01M CaCl₂ solution. So deioned water and 0. 01M CaCl₂ solution can be used as soil extractants to simulate actual soil solution environment when rainfall and irrigation take place. In this paper, measured results extracted by deioned water and 0. 01M CaCl₂ solution are compared with results extracted by saturated CaSO₄ and 2M KC1 solutions in order to clarify the relations among them. Four soil samples, which were gathered in the suburb of Beijing, were blended and shaken for 30 minutes with four extractants (6 extracting forms) (According to traditional methods of soil extraction, the ratio of water to soil is 5 : 1 when saturated CaSO4 solution and 2M KC1 solution were used. The ratios are 20 : 1 and 100 : 1 when deioned water and 0. 01M CaCl₂ solution are used. ). Then the extracted solutions were filtrated by 0. 45μm filter paper. The concentrations of NH₄⁺ and NO₃^- in the filtrate are analyzed with Salicin-hypochlorite Method and Griess-Ilosvay Method by Autoanalyzer Ⅲ Colorimeter (BRAN LUEBBE). According to the measured results, such conclusions are drawn: (1) the measured values of NO₃^- by different extracting methods are coincident with each other; (2) the measured values of NH₄⁺ are obviously different. The values of NH₄⁺ extracted by deioned water (ratio of water to soil is 100 : 1) surpass the others by far; and (3) the measured values of NH₄⁺ extracted by deioned water and 0. 01M CaCl₂ solution are not as stable as the ones by saturated CaSO₄ and 2M KC1 solutions. On the basis of these, four kinds of extractants are fit when a research is centred only on NO₃^-. Or else, fit extractant and ratio of water to soil must be selected according to the goal of the research and characteristics of the researched system.