烧失量法测定土壤有机质含量的实验条件探究

Optimization of the Experiment Conditions for Estimating Organic Matter Content with Loss-on-ignition Method

烧失量法是测定有机质含量的可靠手段,以其方便、快捷、经济等优点被广泛应用于土壤学、地质学、湖泊学等研究中。但由于对煅烧过程的研究较少,煅烧条件的选择不统一,使得不同实验条件下测定结果的可比性较差。本研究使用带烧失称重系统的马弗炉,对中国北方有机质含量不同的三种类型土壤进行了烧失量测定实验,通过观察土壤重量随温度和时间变化的连续失重过程,对煅烧温度、煅烧恒温时长、样品量及升温速率等实验条件进行了系统研究,确立了烧失量法适宜的实验条件组合。实验结果表明：升温速率宜选择3℃/min;样品量建议选用3~5 g,有机物含量低的样品可适量增加;不同类型土壤的适宜煅烧温度略有差别,黑土和栗钙土建议选用550℃,而黑垆土选用500℃或550℃;恒温2h可获得较为稳定的烧失量结果。

Loss-on-ignition（ LOI） is a reliable method for organic matter determinations. It has been widely used in soil science,geology and limnology with advantages of simply,quickly and cost-effectively in determining the organic matter. However,the ignition process has received less attention. And literatures using this method showed a great variability within conditions used by different researchers. Then,the lack of standard method hampered the comparability of different results.The purpose of this study is to evaluate an optimal experiment conditions based on ignition process of samples. Three types of soils with a range of organic matter contents were selected to analyze the organic matter contents under different experiment conditions. Several experiments were carried out to investigate the effect of experimental conditions（ sample mass,heating rate,temperature and time of ignition） on LOI results and combustion curves generated by Muffle furnace system,which have the advantage in capturing the continuous combustion loss with its precision scale.Results show that the ideal set of experimental conditions are： 1） Slower heating rates was preferred and 3 ℃ / min of heating rate was a good option; 2） The sample mass analyzed should be based on the characteristics of the sample,especially its organic matter content; if the sample is low in organic matter,then more sample mass is needed; the proposal is 3-5 g; 3） There are soil-specific temperature requirement for organic matter determination. The optimal ignition temperature depends on the soil source and components. For black soil and chestnut soil,550 ℃ is optimal for organic matter determination. For dark loessial soil,500 ℃ or 550 ℃ is feasible;4） Time of heating at the ignition temperature should be controlled. An accurate and stable weight loss was achieved after 2 h of combustion.