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【目的】pH值是碱土诊断及分类的重要依据。测定天山北麓苏打盐碱化土壤pH值,并分析其影响因素,为盐碱化土壤pH值测定的适应方法提供依据。【方法】采用电位法,对新疆天山北麓典型的碳酸盐含量高、碱性强、盐分类型复杂的苏打盐碱化土壤样本,分别设置不同水土比(1∶1、2.5∶1、5∶1)和不同静置时间(1、5、10、30和60min)进行pH值测定。【结果】1水土比对pH值测定影响较大,但碱性强弱并不是稀释效应的决定性因素,含有较多CaCO_3的氯化物盐样本稀释效应最强,最大pH值增加量达0.57个单位,这种稀释效应主要来自CaCO_3与中性钠盐反应生成的苏打水解。2水土比2.5∶1时,难溶盐类的溶解基本达到稳定;而1∶1水土比不适用于研究区盐碱化土壤的pH值测定。3静置时间对奇台碱土pH值测定的影响小于艾比湖盐土,静置过程中大气CO_2溶解不影响pH值测定结果。【结论】对于天山北麓盐碱土,可设定为5∶1水土比,悬液充分搅拌后即进行pH值测定,其测定精度与实验效率均较高。
【Objective】 pH value is an important basis for the diagnosis and classification of alkaline earth. The pH value of saline-sodic soil in soda north of Tianshan Mountains was determined and its influencing factors were analyzed, which provided the basis for the adaptation method of pH determination of saline soils. 【Method】 Potentiometric method was used to set up a typical saline-alkali soil sample with high carbonate content, strong alkalinity and complex salt types in the northern foot of Tianshan Mountains of Xinjiang. The soil water ratio (1: 1, 2.5: 1, 5: : 1) and different stationary time (1, 5, 10, 30 and 60min). 【Result】 1 Soil-water ratio has a great effect on the determination of pH. However, the alkaline strength is not the decisive factor in the dilution effect. Chloride salts containing more CaCO_3 have the strongest dilution effect, and the maximum pH value increases by 0.57 units , This dilution effect mainly comes from the soda hydrolysis reaction of CaCO 3 with neutral sodium salt. 2 soil-water ratio of 2.5: 1, the dissolution of insoluble salts basically stabilized; and the ratio of 1: 1 soil-water ratio was not suitable for the determination of pH value of saline-alkali soil in the study area. The effect of standing time on the determination of pH in Qitai alkaline soil is less than that in the soil of Lake Aibi. Atmospheric CO 2 dissolution during standing does not affect the results of pH measurement. 【Conclusion】 For the saline-alkali soil in the northern foot of Tianshan Mountains, the ratio of soil to water can be set at 5:1. After the suspension is fully stirred, the pH value is determined. The determination accuracy and experimental efficiency are high.