石灰性土壤交换性钙和镁测定方法的研究

DETERMINATION OF EXCHANGEABLE CALCIUM AND MAGNESIUM IN CALCAREOUS SOIL

石灰性土壤交换性盐基组成的测定,通行的方法是采用70%乙醇溶液反复洗盐,再经pH 8.50.1 mol L-1氯化铵-70%乙醇(CH3CH2OH)溶液进行多次交换处理,测定交换液中的K+、Na+、Ca2+、Mg2+浓度。但此方法常常受操作步骤繁琐,以及土壤中碳酸盐的溶解量因多次浸提而增加的困扰,最终导致测定结果偏高。基于上述原因,选择不同浓度、不同pH的NH4OAc和NH4Cl 10种交换剂,对比分析10种交换剂中的碳酸盐溶解度和土壤交换性钙镁含量。结果表明,pH=8.5 1 mol L-1氯化铵-70%乙醇(CH3CH2OH)溶液较适合石灰性土壤交换性盐基的测定。此新方法是先经70%乙醇(CH3CH2OH)溶液洗盐,再用pH8.5 1 mol L-1氯化铵(NH4Cl)-70%乙醇(CH3CH2OH)溶液进行一次性交换处理,然后测定交换液的K+、Na+、Ca2+、Mg2+浓度,简化了操作程序的同时有效抑制了土壤碳酸盐的溶解,降低了测定结果的偏差。

The commonly used method for determining exchangeable bases is to repeatedly leach a soil sample with 70% ethanol （CH3CH2OH） solution, and then treated with the mixture of 0.1 mol L^-1 ammonium chloride （NH4Cl） and 70% ethanol （CH3CH2OH）, 8.5 in pH, several times for extraction, and in the end, content of K^＋, Na^＋, Ca^2＋ and Mg^2＋in the extractant is determined, separately. However, this method is complicated and time-consuming in operation and repeated extraction may increase dissolution of carbonate in the soil solution, thus making results of the determination tend to be higher. Based on the above-mentioned, tests were conducted of 10 ion exchangers different in concentration of NH4Cl and NH4OAc and in pH for comparison in solubility of carbonates and content of exchangeable Ca^2＋ and Mg^2＋. Results indicate that the mixture of 1mol L^-1 NH4Cl and 70% CH3CH2OH, 8.5 in pH is the most suitable one. The new method goes like this, wash a soil sample off salts with 70% CH3CH2OH first and then treat the sample with the mixture of 1mol L^-1 NH4Cl and 70% CH3CH2OH 8.5 in pH for extraction, only once, and in the end, concentration of K^＋, Na^＋, Ca^2＋ and Mg^2＋in extractant is determined. To sum up, this method not only simplifies the operation procedure, but also effectively inhibits dissolution of carbonate in the calcareous soils, thus lowering deviation of the determination.