重量法测定土壤水溶性盐总量的优化

土壤水溶性盐是表征土壤盐碱化程度的重要指标，也是评价耕地地力的重要参数，被纳入第三次全国土壤普查（“三普”）监测指标体系中。重量法是测定土壤水溶性盐总量的最常用方法，其测定过程易受多种因素影响，导致其测定结果不准。鉴于此，本文设计试验分别验证了水溶性盐浸提和浸提液固液分离这两个过程对测定结果的影响，结果表明浸提液固液分离是影响土壤水溶性盐总量测定准确度和精密度的主要因素。基于此进一步探究4种不同固液分离方式（布氏漏斗过滤、滤膜真空抽滤、离心、滤纸组合过滤）对测定结果的影响，结果表明相较于其它方式，滤纸组合过滤测定结果准确度高，适用于土壤水溶性盐总量的测定。对改进后的重量法测定土壤水溶性盐总量进行方法学确认，结果表明其检出限为0.01 g/kg，测定下限为0.04 g/kg；方法的准确度和精密度、适用范围等均符合相关要求。本文推荐的土壤水溶性盐总量测定方法为：土壤样品采用1:5土水比浸提，180 r/min振荡3 min，浸提液采用滤纸组合自然过滤；其测定结果的准确度和精密度符合相关要求。本文旨在为“三普”内业检测提供参考和借鉴，为全面摸清不同区域土壤水溶性盐含量水平及土壤盐渍化程度提供技术支撑。

Optimization of Water-soluble Salt in Soil by Gravimetric Method

As an important index to characterize the degree of soil salinization and an important parameter to evaluate the cultivated land productivity, soil water-soluble salt has been included in the 3rd National Soil Survey monitoring index system. Gravimetric method is the most primary method for the determination of water-soluble salt in soil, but many factors would have effects on the determination of water-soluble salt, which would resulted in inaccurate results. In view of this, experiments were designed to verify the effects of water-soluble salt extraction and liquid-solid separation on the determination results, respectively. It was proved that liquid-solid separation was the main factor affecting the accuracy and precision of the determination of water-soluble salt in soil. Furthermore, it was explored the influence of four different liquid-solid separation methods, including Brinell funnel filtration, filter membrane vacuum filtration, centrifugation and filter paper combination filtration, on the determination of water-soluble salt in soil. It was showed that compared with other methods, the result of filter paper combination filtration had high accuracy, which was suitable for the determination of water-soluble salt in soil. The limit of detection of water-soluble salt in soil by the improved gravimetric method was 0.01 g/kg, and the limit of quantitation was 0.04 g/kg. More detailed, the accuracy, precision and range of application of the improved gravimetric method meet the relevant requirements. It was recommended method for the determination of water-soluble salt in soil as follow: 1:5 soil-water ratio extraction of soil samples, 180 r/min oscillation for 3 min, and natural filtration of the extract by filter paper combination. The accuracy and precision of the results met the relevant requirements. The purpose of this paper is in order to provide reference for the 3rd National Soil Survey, and to provide technical support for the comprehensive understanding of soil water-soluble salt content level and soil salinization degree in different regions.