土壤交换性钙和镁测定方法的改进研究

Method Improvement for Determination of Soil Exchangeable Calcium and Magnesium

【目的】通过比较不同浸提试剂、离心次数以及振荡时间对土壤交换性钙离子(Ca2+)、镁离子(Mg2+)含量测定结果的影响,简化国标测定方法 GB 7865-1987(2)的操作程序,以适应大批量土壤样品的快速测定。【方法】分别采集中国西北、东北、西南和华南等4个地区的代表性土壤,选取去离子水(H2O)、氯化钙(CaCl2)、氯化钾(KCl)、乙酸铵(NH4OAc)和Mehlich 3 (Me 3)等5种浸提试剂,设定不同的浸提-离心次数(1~6次)和振荡时间(15~60 min),对比土壤交换性Ca2+、Mg2+含量测定结果的差异。【结果】(1)不同的浸提剂对同一土壤交换性Ca2+、Mg2+含量测定结果存在差异,具体表现为Me 3>CaCl2>KCl>NH4OAc>H2O。(2)土壤交换性Ca2+、Mg2+含量测定结果与土壤浸提-离心次数呈正相关关系,增加浸提-离心次数可能会显著提高测定结果。(3)不同类型土壤需匹配不同的浸提-离心次数,如江西(标样)、云南和福建3种土壤的交换性Ca2+、Mg2+含量测定需经4次浸提-离心即达到稳定值,而新疆和黑龙江土壤则需分别经6次(Ca2+)和5次(Mg2+)浸提-离心。(4)土壤经NH4OAc浸提并振荡60 min后测定的交换性Ca2+、Mg2+含量与国标法无差异,且振荡法更加适合大批量样品的测定。【结论】不同浸提剂对土壤交换性Ca2+、Mg2+含量测定结果存在差异;相比国标法,NH4OAc振荡浸提法测定步骤相对简单、对设备要求较低,且测定结果稳定,更适合大批量土壤样品的高效测试需求。

[Purpose]To optimize and simplify the operation procedures of the national standard determination method[GB 7865—1987(2)]for rapid evaluation of large quantities of soil samples by comparing the accuracy and efficiency of different methods in determining the contents of soil exchangeable calcium(Ca2+)and magnesium(Mg2+)in terms of extraction reagents,centrifugation times,and shaking time.[Method]Representative soils were taken from four regions of Northwest,Northeast,Southwest,and South China,and five extraction reagents deionized water(H2O),calcium chloride(CaCl2),potassium chloride(KCl),ammonium acetate(NH4OAc)and Mehlich 3(Me 3)were utilized for method comparison at different extraction-centrifugation time(1-6 times)and shaking time(15-60 min).[Result]1)Exchangeable Ca2+and Mg2+contents for a given soil sample varied with different extractant in the order of Me 3>CaCl2>KCl>NH4OAc>H2O.2)Soil exchangeable Ca2+and Mg2+contents were positively correlated with the extraction-centrifugation times,and increasing the extraction-centrifugation times might give rise to significantly higher values.3)Extraction-centrifugation times depended on soil types.Exchangeable Ca2+and Mg2+contents of soils in Jiangxi(standard sample),Yunnan,and Fujian stabilized after four times of extraction-centrifugation,while the Xinjiang and Heilongjianghe soil needed 6(Ca2+)and 5(Mg2+)times of extraction-centrifugation,respectively.4)Concentrations of exchangeable Ca2+and Mg2+determined by 60 min of NH4OAc extraction and oscillation was comparable to those derived from the national standard method,and the oscillation method was more suitable for large quantities of samples.[Conclusion]Different extraction reagents affect final values of soil exchangeable Ca2+and Mg2+contents.Compared with the national standard method,the NH4OAc oscillation method has relatively less procedures,lower equipment requirements,and reliable results,which is more suitable for highefficiency testing requirements of large quantities of soil samples.