Measured versus estimated total porosity along structure-stability gradients of coarse-textured tropical soils with low-activity clay
Measured versus estimated total porosity along structure-stability gradients of coarse-textured tropical soils with low-activity clay
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DOI：
10.1007/s12665-014-3102-3
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发表时间：
2014-02
影响因子：
2.8
通讯作者：
S. E. Obalum;M. Obi
中科院分区：
文献类型：
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作者：
S. E. Obalum;M. Obi
土壤总孔隙度通常由容重和假定的颗粒密度估算，而不是用水解吸法测量。测量和估计的总孔隙度，甚至高岭石热带土壤（具有低倾向，扩大后润湿）通常不同的程度，取决于土壤结构的稳定性，但这种差异几乎没有记录。对尼日利亚东南部地区不同休闲和耕作管理制度下的70个粗质地土壤样品进行了质地、团聚体平均重量直径（MWD）、BD和有机质（OM）浓度分析。将通过水解吸法测量的土壤总孔隙度与根据BD（颗粒密度固定为2.70 g cm−3）估算的土壤总孔隙度进行比较，在根据结构稳定性对土壤进行分组后，通过OM/（粉土+粘土）对50个来自休耕地块（BD > 1.48 g cm−3）的样品进行评估，并对其余来自耕作地块（BD < 1.48 g cm−3）的样品进行MWD评估。休耕地块显示出比耕作地块更宽的稳定范围。无论土地利用，结构稳定性往往增加减少土壤BD。测量的总孔隙度始终高于其估计值，随着土壤结构稳定性的增加，差异逐渐缩小，直到平均BD为1.41 ± 0.05 g cm−3（对应于MWD为2.66 ± 0.12 mm），超过此值，趋势逆转。这些结果表明，随着土壤结构稳定性的增加，土壤颗粒密度降低，而在称重时饱和样品的滞留空气和暂时排水增加。用2.70 g cm− 3的固定颗粒密度估算总孔隙度似乎仅适用于高度稳定的土壤，BD ≤1.40 ± 0.08 g cm− 3和/或MWD ≥2.92 ± 0.05 mm [相当于OM/（粉土+粘土）≥16.38 ± 0.28%]。
Soil total porosity is, rather than measured by water desorption method, more often estimated from bulk density (BD) and assumed particle density. Measured and estimated total porosities of even kaolinitic tropical soils (which have low tendency to expand upon wetting) usually differ by an extent that depends on soil structural stability, but such differences are scarcely documented. Seventy samples of coarse-textured soils under different fallow- and cultivation-management systems in the southeastern region of Nigeria were analyzed for texture, mean-weight diameter (MWD) of aggregates, BD and organic matter (OM) concentration. Soil total porosities measured by water desorption method were compared with those estimated from BDs (with particle density fixed at 2.70 g cm−3), after grouping the soils by structural stability, assessed by OM/(silt + clay) for 50 of the samples from fallowed plots (BD > 1.48 g cm−3) and MWD for the rest from cultivated plots (BD < 1.48 g cm−3). The fallowed plots showed a wider stability range than the cultivated plots. Irrespective of land use, structural stability tended to increase with decreasing soil BD. Measured total porosities were consistently higher than their estimated counterparts, with the differences closing up with increasing soil structural stability up till a mean BD of 1.41 ± 0.05 g cm−3(corresponding to MWD of 2.66 ± 0.12 mm), beyond which the trend reversed. These results suggest that, as the soil structural stability increases, soil particle density decreases while entrapped air and transitory drainage of saturated samples at weighing increase. Estimating total porosity with a fixed particle density of 2.70 g cm−3appears suitable only in highly stable soils, with BD of ≤1.40 ± 0.08 g cm−3and/or MWD of ≥2.92 ± 0.05 mm [corresponding to OM/(silt + clay) of ≥16.38 ± 0.28 %].