两种土壤导气率测算模型的对比分析

Comparative Analysis on Two Air Permeability Models

土壤导气率是重要、易测量的土壤参数,其价值在于可以预测田间饱和导水率,反映土壤孔隙和土壤结构特征。国内外学者提出不同土壤导气率测算模型。本文通过对比瞬态法和稳态法两种土壤导气率测算模型,分析两模型在测量效率、经济性等方面优缺点,以及测量结果的相对误差变化幅度。瞬态法相对稳态法,无须测量通过土样的气体数量,测量时间短,且只需少量体积的气体通过土样,对土样结构破坏小;而稳态法测量技术较成熟,计算方便。室内对60组土样测算结果表明,瞬态法与稳态法测量结果之间具有极显著的相关性,可用线性函数关系式y=0.979 1 x表示;以稳态法为标准,两种方法测量结果相对误差变化幅度在0.5%-45%之间,80%以上测量结果相对误差变化幅度〈15%,仅有少数变化幅度〉20%;同时,试验结果也验证了稳态试验中气体传导速率Q与测量仪内封闭气体压强值△P存在显著的线性关系,及Kirkham提出的在瞬态模型中被测土样密封端压力动态变化与时间t之间存在线性关系。

Air permeability is an easy but important soil parameter,which can be used as an indicator of Ks at field scale and of soil porosity and soil structural property.So far lots of air permeability models with different properties have been established.This paper compared the constant pressure method and the transient-flow method in measuring air permeability in the measure efficiency andeconomy,the range of relative error of measured result.Comparing to the constant pressure method,the transient-flow method is unnecessary to measure the air quantity through the soil sample,and it cost less time and need only a small volume air going through the sample soil,thus cause less damage to soil sample structure.The constant pressure method embraces the advantage in technique maturity and calculation convenience.The indoor measurment results of 60 soil samples showed the extremely significant correlation between the two methods（y = 0.979 1x）,taking the constant pressure method as a standard,the range of relative error of the measured results between the two methods was between 0.5%-45%,the relative error was less than 15% for more than 80% of measured results.Meanwhile,the test results confirmed the significant linear relation between gaseous conductance rate Q and the gas pressure value △P within admeasuring apparatus by constant pressure method as well as the linear relation between time T and the dynamic change of seal section pressure in the measured soil sample by constant pressure model proposed by Kirkham.