初探土壤有机质测定方法的改进

基于榆林乃至黄土高原地区土壤有机质含量水平普遍偏低的现状，采用经典土壤有机质测定方法，滴定所用的硫酸亚铁（铵）消耗量很大，甚至与空白接近，耗时又消耗化学试剂。笔者选取69个有机质含量在2.0~30 g/kg的土样，采用经典土壤有机质测定方法和减半使用K₂Cr₂O₇-H₂SO₄溶液的情况下测定有机质含量，其他条件不变，进行对比。结果表明，经典方法与改进方法，当有机质含量≤8.7 g/kg时，100%的数据符合平行测定允许差；随着土壤有机质含量增加，2种方法测定土壤有机质含量差异越来越大，当有机质含量＞15.2 g/kg时，修订方法的测定结果均低于经典方法的测定结果，且只有27%的数据能满足平行测定允许差，不宜采用上述测定方法。该有机质测定改进方法，特别是当有机质含量≤8.7 g/kg时，既节约了化学试剂，又节省了配置试剂和滴定所用的时间，提高了工作效率也不影响测定结果的准确性。

Preliminary Study on Modification of Classical Method of Determining Soil Organic Matter

Due to the low content of soil organic matter （SOM） on soils in the loess plateau, the classical method for determining SOM seemed to be inefficient, time-consuming and non economic. Totally, 69 soil samples with SOM ranging from 2.0 to 30 g/kg had been selected to test modification of classical method, which reduced 50% of digestion solution （K2Cr2O7-H2SO4） and kept other procedures unchanged. The results showed that SOM contents determined by modified method were comparable with those determined by classical method when soils had content of soil organic matter below 8.7 g/kg. With SOM content increase, differences of SOM content determined by two methods became larger and larger, and significant lower values determined by modified method than classical method were observed when soils had the content of soil organic matter above 15.2 g/kg. It was concluded that modified method could save time, more efficient and economic for measuring soils with low SOM contents, especially below 8.7 g/kg.