土壤硝态氮含量测定方法的选择和验证

对经典的酚二碳酸法和Ｎｏｒｍａｎ等人提出的紫外分光光度法测定土壤浸提液中硝态氮含量的可行性进行了对比验证。结果表明,用紫外分光光度“差减法”测定土壤侵提液中的硝态氮含量,在精度上能满足测定之需要（与酚二碳酸法相比）;由于供试土壤系列在２７０ｎｍ处的吸光度极低,因而,用Ｒ值校正和不校正结果间的差异不明显;对给定的土壤系列而言,土壤样品在２１０ｎｍ处的吸光率受土壤中其他非硝酸根离子含量的影响不大,因此“直接法”和双波长法的测定结果之间差异可忽略不计;在６０℃条件下鼓风烘干３～４小时,结果与湿士测定间的差异不明显,完全能满足农化服务大批量分析测定之需要。

Selection and Verification of Methods for Determination of Nitrate in Soil Extracts

The comparison sudies were conducted for sellecting a suitable method to determine nitrate concentrtion in a soil extract between the diphenol sulfonic acid and UV spectrophotometry.Results showed that the mean values determined by the "subtractive" UV spetrophotometry were all the same to values determined from diphenol sulfonic acid.The "subtractive" means that the interference of nonnitrate species is accounted for by subtracting the absorbance after treated with Raney-Nicdel catalyst to remove nitrate from its absorbance of no removing nitrate at 210nm.There was no significant difference between the mean nitrate concentrations determined by UV spectrophotometry corrected and uncorrected with R value in this set of soil samples,because of their very low absorbances at 270nm. The further tests for UV spectrophotometric method also indicated that the difference between the results,obtained by the daulwavelength and "directive" method of UV spectrophotomety, was not significant because it was low that abssorbance of extracts at 210nm interfered with the nonnitrate species in the entire set of samples.Most soil samples are taken from field in the spring or winter.How to make the samples quick air drying is a problem in the seasons. Results showed that wet samples were in oven with wind blowing for 3-4 hours at 60℃ and the values obtained from wet and dry samples were quite the same. So the proposed method for sample drying can be used for routine analyses where many samples are involved.