土壤有机质对交换性酸测定结果的影响

为探讨土壤有机质对两种常用的土壤交换性酸测定方法(BaCl_2-TEA提取法和KCl淋溶法)结果的影响,选取了85个不同有机质质量分数的酸性土壤并采用BaCl_2-TEA提取法和KCl淋溶法测定其交换性酸含量.结果表明,BaCl_2-TEA提取法测得的土壤交换性酸含量远大于KCl淋溶法的测定结果.KCl淋溶法测得的土壤交换性酸含量与土壤pH值间的负相关性极有统计学意义(r=-0.79**),而BaCl_2-TEA提取法测得的土壤交换性酸含量与土壤pH值间的相关性无统计学意义(r=-0.08).但BaCl_2-TEA提取法测得的土壤交换性酸含量却与土壤有机质质量分数间的正相关性极有统计学意义(r=0.94**).此外,由KCl淋溶法测得的土壤交换性酸进一步计算得到的盐基饱和度与土壤pH值间的相关性(r=0.69**)也大于BaCl_2-TEA提取法(r=0.25*).通常土壤酸化越严重,土壤pH值越低,交换性酸含量越高,盐基饱和度越低.可以得出,土壤有机质会使BaCl_2-TEA提取法的测定结果产生较大的正误差,而对KCl淋溶法的影响较小.由于土壤有机质中的腐殖酸会与BaCl_2-TEA提取法中的有机弱碱TEA发生反应,增加TEA用量,从而使计算得到的土壤交换性酸的结果偏高.因此,对于高有机质质量分数的酸性土壤,不宜采用BaCl_2-TEA提取法测定其交换性酸含量.但在KCl淋溶法中,由于K~+对Al~(3+)的交换能力较弱,使得该方法测得的土壤交换性酸含量偏低.因此,可乘以1.5左右的校正系数,以便能真实地反映出土壤交换性酸含量.

Influence of Soil Organic Matter on the Measurement of Soil Exchangeable Acidity

In order to investigate the effects of soil organic matter on the measurements of soil exchangeable acidities with different extraction methods, the exchangeable acidities of 85 acidic soils with different contents of organic matter were measured by the BaCl₂-TEA (Triethanolamine) extraction method and the KCl leaching method. The results showed that the contents of soil exchangeable acidity measured by BaCl₂-TEA extraction were much higher than those measured by the KCl leaching method. The correlation between soil pH and soil exchangeable acidities measured by the KCl leaching method (r=0.79^**, p<0.01) was better than that measured by the BaCl₂-TEA extraction method (r=0.08). However, there was a highly significant positive correlation between soil organic matter and soil exchangeable acidities obtained by the BaCl₂-TEA extraction method (r=0.94^**, p<0.01). In addition, the correlation between soil pH and base saturation calculated with the KCl leaching method (r=0.69^**) was higher than that calculated with the BaCl₂-TEA extraction method (r=0.25^*). Generally, when the soil is acidified, the content of soil exchangeable acidity will increase and the base saturation will decrease. The humic acids in soil organic matter can react with TEA and increase the usage of TEA, thus inducing higher content of soil exchangeable acidities. Therefore, the BaCl₂-TEA extraction method is not suitable for the measurement of exchangeable acidity in acidic soil with high content of organic matter. In addition, the soil exchangeable acidity measured by the KCl leaching method was low because of the weakly exchangeable ability of K⁺. Therefore, it is advisable to adjust the content of soil exchangeable acidity measured by the KCl leaching method with a coefficient of 1.5.