Abstract:Nitrite (NO2--N) is a key intermediate in both nitrification and denitrification, which is also closely related to the emission of nitrogen gas from soil. Since its rapid reaction in soil and instability in acidic condition, a large number of decomposition will occur in the extraction process using 2 mol/L KCl. In order to enhance the accuracy of study on NO2--N changes in the acidic soil, a more appropriate extraction method should be investigated to improve the effeciency of the nitrite extraction. In this study, we put forward some suggestions in improving NO2--N extraction based our resutls of NO2--N recovery measured by using 15N-labelling method. The results showed that pH and shaking time could both significantly affect the recovery of NO2--N and NH44+-N in acidic soils. Within 30 min shaking, the recovery of NO2--N was highest in the adjusted pH 6.0 and pH 8.0 treatments, while the recovery of ammonium was highest in the unadjusted and adjusted pH 6.0 treatments. In addition, even after shaking, the pH of extraction solution in the adjusted pH 6.0 and pH 8.0 treatments were maintained at about 4.8 and 5.8, respectively, which were significantly higher than that of control (3.8). In all, the pH of extraction solution should be adjusted to 5.0–6.0 and shaking time should be 30 min to get a more efficient extraction of both NO2--N and NH4+-N. For strongly acidic soils (pH<6.0), a mixture of KCl and pH 8.4 buffer (KCl︰buffer = 4︰1) should be used as extraction solution (the ratio of soil to extraction solution was 1︰5). For alkaline soils (pH≥7.5), a mixture of KCl and pH 7.5 buffer (KCl︰buffer = 4︰1) should be used as extraction solution (the ratio of soil to extraction solution was 1︰5). For the soil samples with pH ranged from 6.0 to 7.5, it can be extracted directly by 2 mol/L KCl solution.