GEOGRAPHICAL RESEARCH ›› 2005, Vol. 24 ›› Issue (2): 236-242.

• Earth Surface Processes •

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

WANG Hong-ping1,4, LIANG Tao2, ZHANG Xiu-mei2, XIA Jun3,4

1. 1. Department of Environment Engineering, School of Resource and Environment, Wuhan University, Wuhan 430079, China;
2. Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China;
3. Key Lab. of Water Cycle &Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China;
4. The State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China
• Received:2004-08-12 Revised:2004-11-25 Online:2005-04-15 Published:2005-04-15

Abstract:

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.