我国耕地中盐碱土分布广泛, 这对现代农业发展和农村建设造成严重制约。 盐碱土壤表层中可溶性盐类(Ca²⁺, K⁺, Na⁺和Mg²⁺)的质量分数一般可以达到0.1%~0.2%以上。 这种土壤中浓度过高的离子通过渗透、 胁迫或者离子毒害, 妨碍植物对其他离子和营养元素的吸收, 危害作物的生长。 因此, 盐碱地改良是现代农业研究的一个重要方向。 准确、 快速测量盐碱土中高含量水溶性盐阳离子K⁺, Ca²⁺, Na⁺和Mg²⁺是盐碱土改良的重要基础和关键技术问题之一。 传统的分析流程是将盐碱土置于水中振荡若干小时后, 取上清液用原子吸收光谱法进行直接测定。 由于原子吸收光谱仪的检出限远远低于待测样品含量, 测试过程中需要进行多次稀释, 增大了测试的系统误差, 降低了实验结果的可信度。 因此, 提出用X射线荧光光谱仪分别测定盐碱土样品中Ca, K, Na和Mg元素的总含量以及一定振荡时间后残渣样品中的K, Ca, Na和Mg元素含量, 计算差值求得可溶性Ca²⁺, K⁺, Na⁺和Mg²⁺含量的方法。 将测试结果与原子吸收光谱法测定的结果进行对比, 并通过pH值、 电导率以及盐碱土中主要阴离子Cl^-, SO42-, HCO3-和CO32-的含量变化特征加以佐证。 结果表明: X射线荧光光谱法测定分别振荡1~6小时后的样品中可溶性Ca²⁺, K⁺, Na⁺, Mg²⁺离子含量并无太大变化, 可以判断在振荡1 h后样品中的可溶性阳离子几乎全部溶出, 且X射线荧光光谱法的测定结果与原子吸收光谱法基本一致。 此外, 通过样品的pH值和电导率在1 h后发生突变, 以及通过离子色谱法和双中和指示剂法得到的盐碱土中主要阴离子含量变化特征也可以验证X射线荧光光谱法的可靠性。 X射线荧光光谱法间接分析盐碱土中高含量水溶性盐阳离子的方法, 具有操作简便、 安全可靠、 准确度高的优点。

Saline-alkali soil is widely distributed in cultivated land in China, which seriously restricts the development of modern agriculture and rural construction. The mass fraction of soluble salts (Ca²⁺, K⁺, Na⁺ and Mg²⁺) in the surface layer of saline soil can reach more than 0.1%~0.2%. The excessive concentration of ions in this soil can hinder the absorption of other ions and nutrients by plants and harm the growth of crops through osmosis, stress or ion poisoning. Therefore, saline-alkali land improvement is an important direction of modern agricultural research. Accurate and rapid measurement of water-soluble cationic Ca²⁺, K⁺, Na⁺ and Mg²⁺ in saline-alkali soil is one of the important foundations and key technical problems for soil improvement. The traditional analytical procedure is oscillating the saline-alkali soil in water for several hours and then taking the supernatant solution for direct determination by atomic absorption spectrometry. As the detection limit of the atomic absorption spectrophotometer is far lower than that of the sample to be tested, multiple dilutions are required in the test process, which increases the systematic error of the test and reduces the credibility of the experimental results. Therefore, in this paper the X-ray fluorescence spectrometer was used to determine the Ca, K, Na and Mg content of original saline-alkali soil sample and residual sample after a certain oscillation time, and then the difference was calculated to obtain the soluble Ca²⁺, K⁺, Na⁺ and Mg²⁺ content. The test results were compared with those determined by atomic absorption spectrometry. The pH, electrical conductivity and the content change characteristics of the main anions Cl^-, SO42-, HCO3- and CO32- in saline-alkali soil were obtained to confirm the method. The results show that by the X-ray fluorescence spectrometry the soluble Ca²⁺, K⁺, Na⁺ and Mg²⁺ ion contents do not change much after respectively oscillation for 1 ~ 6 hours. Almost all soluble cations dissolve after oscillation for 1 hour. The measured results of X-ray fluorescence spectrometry are basically consistent with those of atomic absorption spectrometry. In addition, the reliability of X-ray fluorescence spectrometry can also be verified by the mutations in pH and conductivity of the sample after oscillation for 1 hour, and the content changes of main anions obtained by ion chromatography and double neutralization indicator method. The X-ray fluorescence spectrometry method for indirect analysis of high content water-soluble salt cations in saline-alkali soil has the advantages of simple operation, safety, reliability and high accuracy.