Comparison of Factors Affecting Soil Nitrate Nitrogen and Ammonium Nitrogen Extraction

摘要

Extraction of soil nitrate nitrogen (NO₃ −-N) and ammonium nitrogen (NH₄ +-N) by chemical reagents and their determinations by continuous flow analysis were used to ascertain factors affecting analysis of soil mineral N. In this study, six factors affecting extraction of soil NO₃ −-N and NH₄ +-N were investigated in 10 soils sampled from five arable fields in autumn and spring in northwestern China, with three replications for each soil sample. The six factors were air drying, sieve size (1, 3, and 5 mm), extracting solution [0.01 mol L−1 calcium chloride (CaCl₂), 1 mol L−1 potassium chloride (KCl), and 0.5 mol L−1 potassium sulfate (K₂SO₄)] and concentration (0.5, 1, and 2 mol L−1 KCl), solution-to-soil ratio (5:1, 10:1, and 20:1), shaking time (30, 60, and 120 min), storage time (2, 4, and 6 weeks), and storage temperature (−18 oC, 4 oC, and 25 oC) of extracted solution. The recovery of soil NO₃ −-N and NH₄ +-N was also measured to compare the differences of three extracting reagents (CaCl₂, KCl, and K₂SO₄) for NO₃ −-N and NH₄ +-N extraction. Air drying decreased NO₃ −-N but increased NH₄ +-N concentration in soil. Soil passed through a 3-mm sieve and shaken for 60 min yielded greater NO₃ −-N and NH₄ +-N concentrations compared to other treatments. The concentrations of extracted NO₃ −-N and NH₄ +-N in soil were significantly (P < 0.05) affected by extracting reagents. KCl was found to be most suitable for NO₃ −-N and NH₄ +-N extraction, as it had better recovery for soil mineral N extraction, which averaged 113.3% for NO₃ −-N and 94.9% for NH₄ +-N. K₂SO₄ was not found suitable for NO₃ −-N extraction in soil, with an average recovery as high as 137.0%, and the average recovery of CaCl₂ was only 57.3% for NH₄ +-N. For KCl, the concentration of extracting solution played an important role, and 0.5 mol L−1 KCl could fully extract NO₃ −-N. A ratio of 10:1 of solution to soil was adequate for NO₃ −-N extraction, whereas the NH₄ +-N concentration was almost doubled when the solution-to-soil ratio was increased from 5:1 to 20:1. Storage of extracted solution at −18 °C, 4 °C, and 25 °C had no significant effect (P < 0.05) on NO₃ −-N concentration, whereas the NH₄ +-N concentration varied greatly with storage temperature. Storing the extracted solution at −18 oC obtained significantly (P < 0.05) similar results with that determined immediately for both NO₃ −-N and NH₄ +-N concentrations. Compared with the immediate extraction, the averaged NO₃ −-N concentration significantly (P < 0.05) increased after storing 2, 4, and 6 weeks, respectively, whereas NH₄ +-N varied in the two seasons. In conclusion, using fresh soil passed through a 3-mm sieve and extracted by 0.5 mol L−1 KCl at a solution-to-soil ratio of 10:1 was suitable for extracting NO₃ −-N, whereas the concentration of extracted NH₄ +-N varied with KCl concentration and increased with increasing solution-to-soil ratio. The findings also suggest that shaking for 60 min and immediate determination or storage of soil extract at −18 oC could improve the reliability of NO₃ −-N and NH₄ +-N results.View full textDownload full textKeywordsAmmonium N, chemical methods, nitrate N, soil extractionRelated var addthis_config = { ui_cobrand: "Taylor & Francis Online", services_compact: "citeulike,netvibes,twitter,technorati,delicious,linkedin,facebook,stumbleupon,digg,google,more", pubid: "ra-4dff56cd6bb1830b" }; Add to shortlist Link Permalink http://dx.doi.org/10.1080/00103624.2012.639108